how to make a calculator 10: part 2

open the project

  • I `change directory`_ to the calculator folder_

    cd calculator

  • I use pytest-watcher to run the tests

    uv run pytest-watcher . --now

    the terminal_ shows

    rootdir: .../pumping_python/calculator
configfile: pyproject.toml
collected 10 items

tests/test_calculator.py .....                                [ 50%]
tests/test_calculator_website.py ...                          [ 80%]
tests/test_streamlit_calculator.py ..                         [100%]

======================== 10 passed in X.YZs =========================

  • I open another terminal_ then use uv_ in the calculator folder_

    uv run streamlit run src/streamlit_calculator.py

    the terminal_ shows

    Collecting usage statistics.
To deactivate, set browser.gatherUsageStats to false.


  You can now view your Streamlit app in your browser.

  Local URL: http://localhost:8501
  Network URL: http://ABC.DEF.GHI.JKL:8501
  External URL: http://MNO.PQR.STU.VWX:8501

    I use ctrl/option on the keyboard and click on http://localhost:8501 with the mouse to open the browser and it shows

    Calculator Streamlit Display

test_streamlit_calculator_buttons

I want to add buttons for the numbers and operations.

RED: make it fail

  • I add a new test with an assertion for the first button, in test_streamlit_calculator.py

    Note

    <- is <+- on the keyboard

    14    def test_streamlit_calculator_display(self):
15        tester = streamlit.testing.v1.AppTest.from_file(
16            'src/streamlit_calculator.py'
17        )
18        tester.run()
19
20        display = (
21            tester.main.children[1].proto
22                  .flex_container
23        )
24        self.assertEqual(display.gap_config.gap_size, 1)
25        self.assertEqual(display.direction, 1)
26        self.assertEqual(display.justify, 1)
27        self.assertEqual(display.align, 1)
28        self.assertTrue(display.border)
29
30    def test_streamlit_calculator_buttons(self):
31        tester = streamlit.testing.v1.AppTest.from_file(
32            'src/streamlit_calculator.py'
33        )
34        tester.run()
35
36        self.assertIsNone(tester.button('<-'))
37
38
39# Exceptions seen

    the terminal_ shows KeyError

    KeyError: '<-'

  • I add KeyError to the list of Exceptions seen

    39# Exceptions seen
40# NameError
41# AttributeError
42# AssertionError
43# SyntaxError
44# KeyError

GREEN: make it pass

  • I add a button in streamlit_calculator.py

    4def main():
5    streamlit.title('Calculator')
6    streamlit.container(border=True)
7
8    streamlit.button('<-')

    the terminal_ still shows KeyError

  • `streamlit buttons`_ have a key parameter. I add it

    8    streamlit.button('<-', key='<-')

    the terminal_ shows AssertionError

    AssertionError: Button(key='<-', label='<-') is not None

    the Button object has two keys - key and label

  • I change the assertion in test_streamlit_calculator.py

    36        self.assertIsNone(tester.button('<-').label)

    the terminal_ shows AssertionError

    AssertionError: '<-' is not None

  • I add <- as the expectation

    36        self.assertIsNone(tester.button('<-').label, '<-')

    the terminal_ shows AssertionError

    AssertionError: '<-' is not None : <-

  • I change assertIsNone_ to assertEqual_

    36        self.assertEqual(tester.button('<-').label, '<-')

    the test passes

  • I go to the browser, click refresh

    Calculator Streamlit First Button no column

    I see the button I just added

REFACTOR: make it better

  • I add the label parameter to the button in streamlit_calculator.py

    4def main():
5    streamlit.title('Calculator')
6    streamlit.container(border=True)
7
8    streamlit.button(label='<-', key='<-')

    the test is still green

  • I add an assertion for the next button, in test_streamlit_calculator.py

    30    def test_streamlit_calculator_buttons(self):
31        tester = streamlit.testing.v1.AppTest.from_file(
32            'src/streamlit_calculator.py'
33        )
34        tester.run()
35
36        self.assertEqual(tester.button('<-').label, '<-')
37        self.assertEqual(tester.button('7').label, '7')

    the terminal_ shows KeyError

    KeyError: '7'

  • I add the button to streamlit_calculator.py

    8    streamlit.button(label='<-', key='<-')
9    streamlit.button(label='7', key='7')

    the test passes

  • I click refresh in the browser

    Calculator Streamlit Second Button no column

    the second button is there

  • I add a for loop for all the buttons, in test_streamlit_calculator.py

    34    def test_streamlit_calculator_buttons(self):
35        tester = streamlit.testing.v1.AppTest.from_file(
36            'src/streamlit_calculator.py'
37        )
38        tester.run()
39
40        for key in (
41            '<-', '7', '4', '1', '+/-',
42            'C', '8', '5', '2', '0',
43            'AC', '9', '6', '3', '.',
44            '/', 'X', '-', '+', '=',
45        ):
46            with self.subTest(key=key):
47                self.assertEqual(tester.button(key).label, key)
48
49        self.assertEqual(tester.button('<-').label, '<-')
50        self.assertEqual(tester.button('7').label, '7')

    the terminal_ shows KeyError for 18 sub tests

    ================== 18 failed, 11 passed in X.YZs ===================

  • I add the buttons to streamlit_calculator.py

     4def main():
 5    streamlit.title('Calculator')
 6    streamlit.container(border=True)
 7
 8    streamlit.button(label='<-', key='<-')
 9    streamlit.button(label='7', key='7')
10    streamlit.button(label='4', key='4')
11    streamlit.button(label='1', key='1')
12    streamlit.button(label='+/-', key='+/-')
13
14    streamlit.button(label='C', key='C')
15    streamlit.button(label='8', key='8')
16    streamlit.button(label='5', key='5')
17    streamlit.button(label='2', key='2')
18    streamlit.button(label='0', key='0')
19
20    streamlit.button(label='AC', key='AC')
21    streamlit.button(label='9', key='9')
22    streamlit.button(label='6', key='6')
23    streamlit.button(label='3', key='3')
24    streamlit.button(label='.', key='.')
25
26    streamlit.button(label='/', key='/')
27    streamlit.button(label='X', key='X')
28    streamlit.button(label='-', key='-')
29    streamlit.button(label='+', key='+')
30    streamlit.button(label='=', key='=')
31
32
33if __name__ == '__main__':

    the test passes

  • I make a function to make the buttons

     1import streamlit
 2
 3
 4def add_buttons():
 5    streamlit.button(label='<-', key='<-')
 6    streamlit.button(label='7', key='7')
 7    streamlit.button(label='4', key='4')
 8    streamlit.button(label='1', key='1')
 9    streamlit.button(label='+/-', key='+/-')
10
11    streamlit.button(label='C', key='C')
12    streamlit.button(label='8', key='8')
13    streamlit.button(label='5', key='5')
14    streamlit.button(label='2', key='2')
15    streamlit.button(label='0', key='0')
16
17    streamlit.button(label='AC', key='AC')
18    streamlit.button(label='9', key='9')
19    streamlit.button(label='6', key='6')
20    streamlit.button(label='3', key='3')
21    streamlit.button(label='.', key='.')
22
23    streamlit.button(label='/', key='/')
24    streamlit.button(label='X', key='X')
25    streamlit.button(label='-', key='-')
26    streamlit.button(label='+', key='+')
27    streamlit.button(label='=', key='=')
28
29def main():

  • I call the new function in main

    30def main():
31    streamlit.title('Calculator')
32    streamlit.container(border=True)
33    add_buttons()
34
35    streamlit.button('<-', key='<-')

    the test is still passing

  • the second terminal_ (for the streamlit_ application) shows streamlit.errors.StreamlitDuplicateElementKey

    streamlit.errors.StreamlitDuplicateElementKey:
There are multiple elements with the same key='<-'.
To fix this, please make sure that the key argument is unique for each element you create.

  • I add streamlit.errors.StreamlitDuplicateElementKey to the list of Exceptions seen, in test_streamlit_calculator.py

    49# Exceptions seen
50# NameError
51# AttributeError
52# AssertionError
53# SyntaxError
54# KeyError
55# streamlit.errors.StreamlitDuplicateElementKey

  • I check the browser and see all the buttons and the Exception

  • I remove the buttons from main in streamlit_calculator.py

    30def main():
31    streamlit.title('Calculator')
32    streamlit.container(border=True)
33    add_buttons()
34
35
36if __name__ == '__main__':
37    main()

    the test is still green

  • The second terminal_ still shows streamlit.errors.StreamlitDuplicateElementKey

  • I check the browser

    Calculator Streamlit No Column All Buttons

    I see all the buttons, and problems

    • all the buttons are in one column, simple calculators have 4 columns - 3 for numbers and 1 for operations

    • 2 buttons are missing - addition and subtraction

    • the buttons have different sizes

  • I remove the other two assertions from test_streamlit_calculator_buttons in test_streamlit_calculator.py

    30    def test_streamlit_calculator_buttons(self):
31        tester = streamlit.testing.v1.AppTest.from_file(
32            'src/streamlit_calculator.py'
33        )
34        tester.run()
35
36        for key in (
37            '<-', '7', '4', '1', '+/-',
38            'C', '8', '5', '2', '0',
39            'AC', '9', '6', '3', '.',
40            '/', 'X', '-', '+', '=',
41        ):
42            with self.subTest(key=key):
43                self.assertEqual(tester.button(key).label, key)
44
45
46# Exceptions seen

  • before I continue, there is some repetition to remove. Each test makes the same `streamlit tester object`_. I add it to the `setUp method`_

     5class TestStreamlitCalculator(unittest.TestCase):
 6
 7    def setUp(self):
 8        self.tester = streamlit.testing.v1.AppTest.from_file(
 9            'src/streamlit_calculator.py'
10        )
11        self.tester.run()

  • I use the new class attribute in test_streamlit_calculator_title

    13    def test_streamlit_calculator_title(self):
14        tester = streamlit.testing.v1.AppTest.from_file(
15            'src/streamlit_calculator.py'
16        )
17        tester.run()
18        # self.assertEqual(tester.title[0].value, 'Calculator')
19        self.assertEqual(self.tester.title[0].value, 'Calculator')

    the test is still green

  • I remove the other lines from test_streamlit_calculator_title

    13    def test_streamlit_calculator_title(self):
14        self.assertEqual(self.tester.title[0].value, 'Calculator')
15
16    def test_streamlit_calculator_display(self):

  • I use the new class attribute in test_streamlit_calculator_display

    16    def test_streamlit_calculator_display(self):
17        tester = streamlit.testing.v1.AppTest.from_file(
18            'src/streamlit_calculator.py'
19        )
20        tester.run()
21
22        display = (
23            # tester.main.children[1].proto
24            self.tester.main.children[1].proto
25                .flex_container
26        )
27        self.assertEqual(display.gap_config.gap_size, 1)

    still green

  • I remove the commented line, tester variable and call to tester.run() from test_streamlit_calculator_display

    16    def test_streamlit_calculator_display(self):
17        display = (
18            self.tester.main.children[1].proto
19                .flex_container
20        )
21        self.assertEqual(display.gap_config.gap_size, 1)
22        self.assertEqual(display.direction, 1)
23        self.assertEqual(display.justify, 1)
24        self.assertEqual(display.align, 1)
25        self.assertTrue(display.border)
26
27    def test_streamlit_calculator_buttons(self):

  • I do the same thing in test_streamlit_calculator_buttons

    27    def test_streamlit_calculator_buttons(self):
28        tester = streamlit.testing.v1.AppTest.from_file(
29            'src/streamlit_calculator.py'
30        )
31        tester.run()
32
33        for key in (
34            '<-', '7', '4', '1', '+/-',
35            'C', '8', '5', '2', '0',
36            'AC', '9', '6', '3', '.',
37            '/', 'X', '-', '+', '=',
38        ):
39            with self.subTest(key=key):
40                # self.assertEqual(tester.button(key).label, key)
41                self.assertEqual(self.tester.button(key).label, key)

    green

  • I remove the commented line, tester variable and call to tester.run() from test_streamlit_calculator_buttons

    27    def test_streamlit_calculator_buttons(self):
28        for key in (
29            '<-', '7', '4', '1', '+/-',
30            'C', '8', '5', '2', '0',
31            'AC', '9', '6', '3', '.',
32            '/', 'X', '-', '+', '=',
33        ):
34            with self.subTest(key=key):
35                self.assertEqual(self.tester.button(key).label, key)
36
37
38# Exceptions seen

    on to columns

test_streamlit_calculator_columns_and_buttons

Calculator buttons are arranged in Columns and Rows. I can use `streamlit columns`_ to arrange the buttons.

RED: make it fail

I add a new test to make sure the Calculator has 4 columns

34            with self.subTest(key=key):
35                self.assertEqual(self.tester.button(key).label, key)
36
37    def test_streamlit_calculator_columns(self):
38        self.assertEqual(len(self.tester.columns), 4)
39
40
41# Exceptions seen

the terminal_ shows AssertionError

AssertionError: 0 != 4

  • len(self.tester.columns) returns the length of the columns object

  • `streamlit columns`_ are lists and I know how to work with lists

GREEN: make it pass

I add columns to the main function in streamlit_calculator.py

30def main():
31    streamlit.title('Calculator')
32    streamlit.container(border=True)
33    add_buttons()
34
35    streamlit.columns(4)
36
37
38if __name__ == '__main__':
39    main()

the test passes

REFACTOR: make it better

  • I add an assertion to check what is in the first column, in test_streamlit_calculator.py

    37    def test_streamlit_calculator_columns(self):
38        self.assertEqual(len(self.tester.columns), 4)
39
40        self.assertIsNone(self.tester.columns[0].children)

    the terminal_ shows AssertionError

    AssertionError: {} is not None

  • I add the expectation

    40        self.assertIsNone(self.tester.columns[0].children, {})

  • I change assertIsNone_ to assertEqual_

    37    def test_streamlit_calculator_columns(self):
38        self.assertEqual(len(self.tester.columns), 4)
39
40        self.assertEqual(
41            self.tester.columns[0].children, {}
42        )

    the test passes

  • I name the columns because I want to put buttons in them, in streamlit_calculator.py

    29def main():
30    streamlit.title('Calculator')
31    streamlit.container(border=True)
32    add_buttons()
33
34    column_1, column_2, column_3, operations = streamlit.columns(4)

    the test is still green

  • I move the columns to the add_buttons function

     4def add_buttons():
 5    column_1, column_2, column_3, operations = streamlit.columns(4)
 6
 7    streamlit.button('<-', key='<-')
 8    streamlit.button('7', key='7')
 9    streamlit.button('4', key='4')
10    streamlit.button('1', key='1')
11    streamlit.button('+/-', key='+/-')

    still green

  • I add the button for <- to the first column

     4def add_buttons():
 5    column_1, column_2, column_3, operations = streamlit.columns(4)
 6
 7    # streamlit.button('<-', key='<-')
 8    column_1.button('<-', key='<-')
 9    streamlit.button('7', key='7')
10    streamlit.button('4', key='4')
11    streamlit.button('1', key='1')
12    streamlit.button('+/-', key='+/-')

    the terminal_ shows AssertionError

    AssertionError: {0: Button(key='<-', label='<-')} != {}

    good, the button is in the column and I know how to test buttons

  • I change the assertion in test_streamlit_calculator_columns in test_streamlit_calculator.py

    37    def test_streamlit_calculator_columns(self):
38        self.assertEqual(len(self.tester.columns), 4)
39
40        self.assertEqual(
41            self.tester.columns[0].button('<-').label,
42            ''
43        )

    the terminal_ shows AssertionError

    AssertionError: '<-' != ''

  • I change the expectation of the assertion

    40        self.assertEqual(
41            self.tester.columns[0].button('<-').label,
42            '<-'
43        )

    the test passes

  • I add a for loop for all the buttons in the first column, in test_streamlit_calculator.py

    37    def test_streamlit_calculator_columns(self):
38        self.assertEqual(len(self.tester.columns), 4)
39
40        for key in ('<-', '7', '4', '1', '+/-'):
41            with self.subTest(key=key):
42                self.assertEqual(
43                    self.tester.columns[0].button(key).label,
44                    'BOOM!!!'
45                )
46
47        self.assertEqual(
48            self.tester.columns[0].button('<-').label,
49            '<-'
50        )

    the terminal_ shows AssertionError for the <- button

    SUBFAILED(key='<-') ... - AssertionError: '<-' != 'BOOM!!!'

    and KeyError

    SUBFAILED(key='7') ... - KeyError: '7'
SUBFAILED(key='4') ... - KeyError: '4'
SUBFAILED(key='1') ... - KeyError: '1'
SUBFAILED(key='+/-') ... - KeyError: '+/-'

  • I change the expectation of the assertion

    42                self.assertEqual(
43                    self.tester.columns[0].button(key).label,
44                    key
45                )

    the terminal_ still shows KeyError

  • I remove the commented line in the add_buttons function then move buttons to the first column in streamlit_calculator.py

     4def add_buttons():
 5    column_1, column_2, column_3, operations = streamlit.columns(4)
 6
 7    column_1.button('<-', key='<-')
 8    column_1.button('7', key='7')
 9    column_1.button('4', key='4')
10    column_1.button('1', key='1')
11    column_1.button('+/-', key='+/-')
12
13    streamlit.button('C', key='C')

    the test passes

  • I add a function for the buttons in the first column

     1import streamlit
 2
 3
 4def add_buttons_to_column_1(column_1):
 5    column_1.button(label='<-', key='<-')
 6    column_1.button(label='7', key='7')
 7    column_1.button(label='4', key='4')
 8    column_1.button(label='1', key='1')
 9    column_1.button(label='+/-', key='+/-')
10
11
12def add_buttons():

  • I call the new function in the add_buttons function

    12def add_buttons():
13    column_1, column_2, column_3, operations = streamlit.columns(4)
14
15    add_buttons_to_column_1(column_1)
16    column_1.button(label='<-', key='<-')

    the terminal_ shows KeyError and streamlit.errors.StreamlitDuplicateElementKey

  • I remove the buttons for column 1 from the add_buttons function since add_buttons_to_column_1 now makes them

    12def add_buttons():
13    column_1, column_2, column_3, operations = streamlit.columns(4)
14
15    add_buttons_to_column_1(column_1)
16
17    streamlit.button(label='C', key='C')

    the test is green again

  • I check the browser and the buttons still look the same

  • I remove the assertion after the for loop, then add another for loop for the second column, in test_streamlit_calculator.py

    37    def test_streamlit_calculator_columns(self):
38        self.assertEqual(len(self.tester.columns), 4)
39
40        for key in ('<-', '7', '4', '1', '+/-'):
41            with self.subTest(key=key):
42                self.assertEqual(
43                    self.tester.columns[0].button(key).label,
44                    key
45                )
46
47        for key in ('<-', '7', '4', '1', '+/-'):
48            with self.subTest(key=key):
49                self.assertEqual(
50                    self.tester.columns[1].button(key).label,
51                    key
52                )
53
54
55# Exceptions seen

    the terminal_ shows KeyError

    SUBFAILED(key='<-') ... - KeyError: '<-'
SUBFAILED(key='7') ... - KeyError: '7'
SUBFAILED(key='4') ... - KeyError: '4'
SUBFAILED(key='1') ... - KeyError: '1'
SUBFAILED(key='+/-') ... - KeyError: '+/-'

  • I move buttons to the second column in streamlit_calculator,py

     2def add_buttons():
 3    column_1, column_2, column_3, operations = streamlit.columns(4)
 4
 5    add_buttons_to_column_1(column_1)
 6
 7    column_2.button(label='C', key='C')
 8    column_2.button(label='8', key='8')
 9    column_2.button(label='5', key='5')
10    column_2.button(label='2', key='2')
11    column_2.button(label='0', key='0')
12
13    streamlit.button(label='AC', key='AC')

    the terminal_ shows KeyError

    SUBFAILED(key='C') ... - KeyError: 'C'
SUBFAILED(key='8') ... - KeyError: '8'
SUBFAILED(key='5') ... - KeyError: '5'
SUBFAILED(key='2') ... - KeyError: '2'
SUBFAILED(key='0') ... - KeyError: '0'

  • I use the keys for the second column, in test_streamlit_calculator.py

    47        for key in ('C', '8', '5', '2', '0'):
48            with self.subTest(key=key):
49                self.assertEqual(
50                    self.tester.columns[1].button(key).label,
51                    key
52                )

    the test passes

  • I check the browser

    Calculator 2 Columns

    there is a second column of buttons. Progress! It does not look right yet, baby steps.

  • I add a function for adding buttons to the second column in streamlit_calculator.py

     4def add_buttons_to_column_1(column_1):
 5    column_1.button(label='<-', key='<-')
 6    column_1.button(label='7', key='7')
 7    column_1.button(label='4', key='4')
 8    column_1.button(label='1', key='1')
 9    column_1.button(label='+/-', key='+/-')
10
11
12def add_buttons_to_column_2(column_2):
13    column_2.button(label='C', key='C')
14    column_2.button(label='8', key='8')
15    column_2.button(label='5', key='5')
16    column_2.button(label='2', key='2')
17    column_2.button(label='0', key='0')
18
19
20def add_buttons():

  • I call add_buttons_to_column_2 in the add_buttons function

    20def add_buttons():
21    column_1, column_2, column_3, operations = streamlit.columns(4)
22
23    add_buttons_to_column_1(column_1)
24    add_buttons_to_column_2(column_2)
25
26    column_2.button(label='C', key='C')

    the terminal_ shows KeyError and streamlit.errors.StreamlitDuplicateElementKey

  • I remove the buttons for the second column from the add_buttons function

    20def add_buttons():
21    column_1, column_2, column_3, operations = streamlit.columns(4)
22
23    add_buttons_to_column_1(column_1)
24    add_buttons_to_column_2(column_2)
25
26    streamlit.button(label='AC', key='AC')

    the test is green again

  • I add a for loop for the third column in test_streamlit_calculator.py

    47        for key in ('C', '8', '5', '2', '0'):
48            with self.subTest(key=key):
49                self.assertEqual(
50                    self.tester.columns[1].button(key).label,
51                    key
52                )
53
54        for key in ('AC', '9', '6', '3', '.'):
55            with self.subTest(key=key):
56                self.assertEqual(
57                    self.tester.columns[1].button(key).label,
58                    key
59                )
60
61
62# Exceptions seen

    the terminal_ shows KeyError

    SUBFAILED(key='AC') ... - KeyError: 'AC'
SUBFAILED(key='9') ... - KeyError: '9'
SUBFAILED(key='6') ... - KeyError: '6'
SUBFAILED(key='3') ... - KeyError: '3'
SUBFAILED(key='.') ... - KeyError: '.'

  • I change the column in the assertion

    54        for key in ('AC', '9', '6', '3', '.'):
55            with self.subTest(key=key):
56                self.assertEqual(
57                    self.tester.columns[2].button(key).label,
58                    key
59                )

    the terminal_ still shows KeyError

  • I move buttons to the third column in the add_buttons function in streamlit_calculator.py

    20def add_buttons():
21    column_1, column_2, column_3, operations = streamlit.columns(4)
22
23    add_buttons_to_column_1(column_1)
24    add_buttons_to_column_2(column_2)
25
26    column_3.button(label='AC', key='AC')
27    column_3.button(label='9', key='9')
28    column_3.button(label='6', key='6')
29    column_3.button(label='3', key='3')
30    column_3.button(label='.', key='.')
31
32    streamlit.button(label='/', key='/')

    the test passes

  • I check the browser

    Calculator 3 Columns

    3 columns

  • I add a function for adding buttons to the third column

    12def add_buttons_to_column_2(column_2):
13    column_2.button(label='C', key='C')
14    column_2.button(label='8', key='8')
15    column_2.button(label='5', key='5')
16    column_2.button(label='2', key='2')
17    column_2.button(label='0', key='0')
18
19
20def add_buttons_to_column_3(column_3):
21    column_3.button(label='AC', key='AC')
22    column_3.button(label='9', key='9')
23    column_3.button(label='6', key='6')
24    column_3.button(label='3', key='3')
25    column_3.button(label='.', key='.')
26
27
28def add_buttons():

  • I call the new function in the add_buttons function

    28def add_buttons():
29    column_1, column_2, column_3, operations = streamlit.columns(4)
30
31    add_buttons_to_column_1(column_1)
32    add_buttons_to_column_2(column_2)
33    add_buttons_to_column_3(column_3)
34
35    column_3.button(label='AC', key='AC')

    the terminal_ shows KeyError and streamlit.errors.StreamlitDuplicateElementKey

  • I remove the buttons for column 3 from the add_buttons function

    28def add_buttons():
29    column_1, column_2, column_3, operations = streamlit.columns(4)
30
31    add_buttons_to_column_1(column_1)
32    add_buttons_to_column_2(column_2)
33    add_buttons_to_column_3(column_3)
34
35    streamlit.button(label='/', key='/')

    the test is green again. On to the next one.

  • I add a for loop with an assertion for the operations in the operations column, in test_streamlit_calculator.py

    54        for key in ('AC', '9', '6', '3', '.'):
55            with self.subTest(key=key):
56                self.assertEqual(
57                    self.tester.columns[2].button(key).label,
58                    key
59                )
60
61        for key in ('/', 'X', '-', '+', '='):
62            with self.subTest(key=key):
63                self.assertEqual(
64                    self.tester.columns[3].button(key).label,
65                    key
66                )
67
68
69# Exceptions seen

    the terminal_ shows KeyError

    SUBFAILED(key='/') ... - KeyError: '/'
SUBFAILED(key='X') ... - KeyError: 'X'
SUBFAILED(key='-') ... - KeyError: '-'
SUBFAILED(key='+') ... - KeyError: '+'
SUBFAILED(key='=') ... - KeyError: '='

  • I move the buttons to the fourth column, in streamlit_calculator.py

    23    column_3.button('.', key='.')
24
25    operations.button('/', key='/')
26    operations.button('X', key='X')
27    operations.button('-', key='-')
28    operations.button('+', key='+')
29    operations.button('=', key='=')
30
31
32def main():

    the test passes

  • I look in the browser

    Calculator 4 Columns

    there are 4 columns

  • I add a function to add buttons to the fourth column, in streamlit_calculator.py

    20def add_buttons_to_column_3(column_3):
21    column_3.button(label='AC', key='AC')
22    column_3.button(label='9', key='9')
23    column_3.button(label='6', key='6')
24    column_3.button(label='3', key='3')
25    column_3.button(label='.', key='.')
26
27
28def add_buttons_to_column_4(column_4):
29    column_4.button(label='/', key='/')
30    column_4.button(label='X', key='X')
31    column_4.button(label='-', key='-')
32    column_4.button(label='+', key='+')
33    column_4.button(label='=', key='=')
34
35
36def add_buttons():

  • I use add_buttons_to_column_4 in the add_buttons function

    36def add_buttons():
37    column_1, column_2, column_3, operations = streamlit.columns(4)
38
39    add_buttons_to_column_1(column_1)
40    add_buttons_to_column_2(column_2)
41    add_buttons_to_column_3(column_3)
42    add_buttons_to_column_4(operations)
43
44    operations.button(label='/', key='/')

    the terminal_ shows KeyError and streamlit.errors.StreamlitDuplicateElementKey

  • I remove the buttons for the fourth column from the add_buttons function

    36def add_buttons():
37    column_1, column_2, column_3, operations = streamlit.columns(4)
38
39    add_buttons_to_column_1(column_1)
40    add_buttons_to_column_2(column_2)
41    add_buttons_to_column_3(column_3)
42    add_buttons_to_column_4(operations)
43
44
45def main():

  • I write the statements in the add_buttons function in the main function

    45def main():
46    streamlit.title('Calculator')
47    streamlit.container(border=True)
48    # add_buttons()
49
50    column_1, column_2, column_3, operations = streamlit.columns(4)
51    add_buttons_to_column_1(column_1)
52    add_buttons_to_column_2(column_2)
53    add_buttons_to_column_3(column_3)
54    add_buttons_to_column_4(operations)

    the test is still green

  • I remove the commented line

    365def main():
366    streamlit.title('Calculator')
367    streamlit.container(border=True)
368
369    column_1, column_2, column_3, operations = streamlit.columns(4)
370    add_buttons_to_column_1(column_1)
371    add_buttons_to_column_2(column_2)
372    add_buttons_to_column_3(column_3)
373    add_buttons_to_column_4(operations)
374
375
376if __name__ == '__main__':
377    main()

  • I remove the add_buttons function because I no longer need it

    28def add_buttons_to_column_4(column_4):
29    column_4.button(label='/', key='/')
30    column_4.button(label='X', key='X')
31    column_4.button(label='-', key='-')
32    column_4.button(label='+', key='+')
33    column_4.button(label='=', key='=')
34
35
36def main():

  • I remove test_streamlit_calculator_buttons because test_streamlit_calculator_columns tests the same things - the button labels, in test_streamlit_calculator.py

    16    def test_streamlit_calculator_display(self):
17        display = (
18            self.tester.main.children[1].proto
19                .flex_container
20        )
21        self.assertEqual(display.gap_config.gap_size, 1)
22        self.assertEqual(display.direction, 1)
23        self.assertEqual(display.justify, 1)
24        self.assertEqual(display.align, 1)
25        self.assertTrue(display.border)
26
27    def test_streamlit_calculator_columns(self):

  • I change the name of test_streamlit_calculator_columns to test_streamlit_calculator_columns_and_buttons

    16    def test_streamlit_calculator_display(self):
17        display = (
18            self.tester.main.children[1].proto
19                .flex_container
20        )
21        self.assertEqual(display.gap_config.gap_size, 1)
22        self.assertEqual(display.direction, 1)
23        self.assertEqual(display.justify, 1)
24        self.assertEqual(display.align, 1)
25        self.assertTrue(display.border)
26
27    def test_streamlit_calculator_columns_and_buttons(self):
28        self.assertEqual(len(self.tester.columns), 4)
29
30        for key in ('<-', '7', '4', '1', '+/-'):
31            with self.subTest(key=key):
32                self.assertEqual(
33                    self.tester.columns[0].button(key).label,
34                    key
35                )
36
37        for key in ('C', '8', '5', '2', '0'):
38            with self.subTest(key=key):
39                self.assertEqual(
40                    self.tester.columns[1].button(key).label,
41                    key
42                )
43
44        for key in ('AC', '9', '6', '3', '.'):
45            with self.subTest(key=key):
46                self.assertEqual(
47                    self.tester.columns[2].button(key).label,
48                    key
49                )
50
51        for key in ('/', 'X', '-', '+', '='):
52            with self.subTest(key=key):
53                self.assertEqual(
54                    self.tester.columns[3].button(key).label,
55                    key
56                )
57
58
59# Exceptions seen

  • All the for loops in test_streamlit_calculator_columns_and_buttons look like this

    for key in (A, B, C, D, E):
    with self.subTest(key=key):
        self.assertEqual(
            self.tester.columns[index].button(key).label,
            key
        )

    I add 2 new for loops that put all the for loops for testing the buttons together

    27    def test_streamlit_calculator_columns_and_buttons(self):
28        self.assertEqual(len(self.tester.columns), 4)
29
30        for column, keys in (
31            (0, ('<-', '7', '4', '1', '+/-')),
32            (1, ('C', '8', '5', '2', '0')),
33            (2, ('AC', '9', '6', '3', '.')),
34            (3, ('/', 'X', '-', '+', '=')),
35        ):
36            for key in keys:
37                with self.subTest(key=key):
38                    self.assertEqual(
39                        (
40                            self.tester.columns[column]
41                                .button(key)
42                                .label
43                        ),
44                        'BOOM!!!'
45                    )
46
47        for key in ('<-', '7', '4', '1', '+/-'):

    the terminal_ shows AssertionError for 20 sub tests

    ================== 20 failed, 11 passed in X.YZs ===================

  • I change the expectation

    38                    self.assertEqual(
39                        (
40                            self.tester.columns[column]
41                                .button(key)
42                                .label
43                        ),
44                        key
45                    )

    the test passes

  • I remove the other for loops

    27    def test_streamlit_calculator_columns_and_buttons(self):
28        self.assertEqual(len(self.tester.columns), 4)
29
30        for column, keys in (
31            (0, ('<-', '7', '4', '1', '+/-')),
32            (1, ('C', '8', '5', '2', '0')),
33            (2, ('AC', '9', '6', '3', '.')),
34            (3, ('/', 'X', '-', '+', '=')),
35        ):
36            for key in keys:
37                with self.subTest(key=key):
38                    self.assertEqual(
39                        (
40                            self.tester.columns[column]
41                                .button(key)
42                                .label
43                        ),
44                        key
45                    )
46
47
48# Exceptions seen

how to change the size of streamlit buttons

I want all the buttons to be the same size.

  • `streamlit buttons`_ have a width option. I set it to stretch for the <- button in the add_buttons_to_column_1 function in streamlit_calculator.py

    4def add_buttons_to_column_1(column_1):
5    column_1.button(label='<-', key='<-', width='stretch')
6    column_1.button(label='7', key='7')
7    column_1.button(label='4', key='4')
8    column_1.button(label='1', key='1')
9    column_1.button(label='+/-', key='+/-')

    the test is still green

  • I refresh the browser

    Calculator Stretched First

    better

  • I stretch the rest of the buttons in the first column

     4def add_buttons_to_column_1(column_1):
 5    column_1.button(label='<-', key='<-', width='stretch')
 6    column_1.button(label='7', key='7')
 7    column_1.button(label='4', key='4')
 8    column_1.button(label='1', key='1')
 9    column_1.button(label='+/-', key='+/-')
10
11
12def add_buttons_to_column_2(column_2):

    still green

  • I check the browser

    Calculator Stretched First Column

    all the buttons in the first column have the same size

  • I stretch the buttons in the second column

    12def add_buttons_to_column_2(column_2):
13    column_2.button(label='C', key='C', width='stretch')
14    column_2.button(label='8', key='8', width='stretch')
15    column_2.button(label='5', key='5', width='stretch')
16    column_2.button(label='2', key='2', width='stretch')
17    column_2.button(label='0', key='0', width='stretch')
18
19
20def add_buttons_to_column_3(column_3):

    green

  • I stretch the buttons in the third column

    20def add_buttons_to_column_3(column_3):
21    column_3.button(label='AC', key='AC', width='stretch')
22    column_3.button(label='9', key='9', width='stretch')
23    column_3.button(label='6', key='6', width='stretch')
24    column_3.button(label='3', key='3', width='stretch')
25    column_3.button(label='.', key='.', width='stretch')
26
27
28def add_buttons_to_column_4(column_4):

    still green

  • I stretch the buttons in the fourth column

    28def add_buttons_to_column_4(column_4):
29    column_4.button(label='/', key='/', width='stretch')
30    column_4.button(label='X', key='X', width='stretch')
31    column_4.button(label='-', key='-', width='stretch')
32    column_4.button(label='+', key='+', width='stretch')
33    column_4.button(label='=', key='=', width='stretch')
34
35
36def main():

    the tests are still green

  • I refresh the browser

    Calculator Streamlit Stretch 4 Columns

    Good! The buttons all have the same size. I am still missing - and + that the tests says are there

how to use raw strings and escape characters

  • I add r and \ to escape the - character because it means something to streamlit_, which is why it does not show on the button in the add_buttons_to_column_4 function

    28def add_buttons_to_column_4(column_4):
29    column_4.button(label='/', key='/', width='stretch')
30    column_4.button(label='X', key='X', width='stretch')
31    column_4.button(label=r'\-', key=r'\-', width='stretch')
32    column_4.button(label='+', key='+', width='stretch')
33    column_4.button(label='=', key='=', width='stretch')

    the terminal_ shows KeyError

    KeyError: '-'

  • I change the - to r'\-' in test_streamlit_calculator_columns_and_buttons in test_streamlit_calculator.py

    27    def test_streamlit_calculator_columns_and_buttons(self):
28        self.assertEqual(len(self.tester.columns), 4)
29
30        for column, keys in (
31            (0, ('<-', '7', '4', '1', '+/-')),
32            (1, ('C', '8', '5', '2', '0')),
33            (2, ('AC', '9', '6', '3', '.')),
34            # (3, ('/', 'X', '-', '+', '=')),
35            (3, ('/', 'X', r'\-', '+', '=')),
36        ):
37            for key in keys:

    the test passes

    • r makes this a raw string_ which means the characters are taken as they are, not what they stand for

    • \ escapes the character so that - is taken exactly as it is to show the character on the button. '-' means something different in streamlit_ so it does not show up as a label for the button

  • I add r and \ to escape the + character because it means something to streamlit_, which is why it does not show on the button in the add_buttons_to_column_4 function, in streamlit_calculator.py

    28def add_buttons_to_column_4(column_4):
29    column_4.button(label='/', key='/', width='stretch')
30    column_4.button(label='X', key='X', width='stretch')
31    column_4.button(label=r'\-', key=r'\-', width='stretch')
32    column_4.button(label=r'\+', key=r'\+', width='stretch')
33    column_4.button(label='=', key='=', width='stretch')

    the terminal_ shows KeyError

    KeyError: '+'

  • I change the + to r'\+' in test_streamlit_calculator_columns_and_buttons in test_streamlit_calculator.py

    27    def test_streamlit_calculator_columns_and_buttons(self):
28        self.assertEqual(len(self.tester.columns), 4)
29
30        for column, keys in (
31            (0, ('<-', '7', '4', '1', '+/-')),
32            (1, ('C', '8', '5', '2', '0')),
33            (2, ('AC', '9', '6', '3', '.')),
34            # (3, ('/', 'X', '-', '+', '=')),
35            # (3, ('/', 'X', r'\-', '+', '=')),
36            (3, ('/', 'X', r'\-', r'\+', '=')),
37        ):
38            for key in keys:

    the test passes

    • r makes this a raw string_ which means the characters are taken as they are, not what they stand for

    • \ escapes the character so that + is taken exactly as it is to show the character on the button. '+' means something different in streamlit_ so it does not show up as a label for the button

  • I remove the commented lines

    27    def test_streamlit_calculator_columns_and_buttons(self):
28        self.assertEqual(len(self.tester.columns), 4)
29
30        for column, keys in (
31            (0, ('<-', '7', '4', '1', '+/-')),
32            (1, ('C', '8', '5', '2', '0')),
33            (2, ('AC', '9', '6', '3', '.')),
34            (3, ('/', 'X', r'\-', r'\+', '=')),
35        ):
36            for key in keys:
37                with self.subTest(key=key):
38                    self.assertEqual(
39                        (
40                            self.tester.columns[column]
41                                .button(key)
42                                .label
43                        ),
44                        key
45                    )
46
47
48# Exceptions seen

  • I check the browser

    Calculator Streamlit All labels

    yes! The calculator shows all the labels.

test_streamlit_calculator_operations_buttons

I want to change the colors of the buttons in the operations column

RED: make it fail

I add a test for the type parameter of `streamlit buttons`_

27      def test_streamlit_calculator_columns_and_buttons(self):
28          self.assertEqual(len(self.tester.columns), 4)
29
30          for column, keys in (
31              (0, ('<-', '7', '4', '1', '+/-')),
32              (1, ('C', '8', '5', '2', '0')),
33              (2, ('AC', '9', '6', '3', '.')),
34              (3, ('/', 'X', r'\-', r'\+', '=')),
35          ):
36              for key in keys:
37                  with self.subTest(key=key):
38                      self.assertEqual(
39                          (
40                              self.tester.columns[column]
41                                  .button(key)
42                                  .label
43                          ),
44                          key
45                      )
46
47      def test_streamlit_calculator_operations_buttons(self):
48          self.assertEqual(self.tester.button('/').proto.type, '')
49
50
51  # Exceptions seen

the terminal_ shows AssertionError

AssertionError: 'secondary' != ''

GREEN: make it pass

I change the expectation

47      def test_streamlit_calculator_operations_buttons(self):
48          self.assertEqual(
49              self.tester.button('/').proto.type,
50              'secondary'
51          )

the test passes

REFACTOR: make it better

  • I change the expectation from secondary to primary

    48        self.assertEqual(
49            self.tester.button('/').proto.type,
50            'primary'
51        )

    the terminal_ shows AssertionError

    AssertionError: 'secondary' != 'primary'

  • I use the type parameter of `streamlit buttons`_ to change the colors of the buttons for the / button in the add_buttons_to_column_4 function, in streamlit_calculator.py

    28def add_buttons_to_column_4(column_4):
29    column_4.button(
30        label='/', key='/', width='stretch', type='primary'
31    )
32    column_4.button(label='X', key='X', width='stretch')
33    column_4.button(label=r'\-', key=r'\-', width='stretch')
34    column_4.button(label=r'\+', key=r'\+', width='stretch')
35    column_4.button(label='=', key='=', width='stretch')

    the test passes

  • I refresh the browser

    Calculator Streamlit First Primary Button

    good

  • I add a for loop for all the buttons in the operations column

    46    def test_streamlit_calculator_operations_buttons(self):
47        for key in ('/', 'X', r'\-', r'\+', '='):
48            with self.subTest(key=key):
49                self.assertEqual(
50                    self.tester.button(key).proto.type,
51                    'primary'
52                )

    the terminal_ shows AssertionError

    SUBFAILED(key='X') ... - AssertionError: 'secondary' != 'primary'
SUBFAILED(key='\\-') ... - AssertionError: 'secondary' != 'primary'
SUBFAILED(key='\\+') ... - AssertionError: 'secondary' != 'primary'
SUBFAILED(key='=') ... - AssertionError: 'secondary' != 'primary'

  • I add the type parameter to the buttons in the add_buttons_to_column_4 function in streamlit_calculator.py

    28def add_buttons_to_column_4(column_4):
29    column_4.button(
30        label='/', key='/', width='stretch', type='primary'
31    )
32    column_4.button(
33        label='X', key='X', width='stretch', type='primary',
34    )
35    column_4.button(
36        label=r'\-', key=r'\-', width='stretch', type='primary',
37    )
38    column_4.button(
39        label=r'\+', key=r'\+', width='stretch', type='primary',
40    )
41    column_4.button(
42        label='=', key='=', width='stretch', type='primary',
43    )
44
45
46def main():

    the test passes

  • I want the C and AC buttons to have the same colors as the buttons for the operations. I add them to the tuple_ in test_streamlit_calculator.py

    47    def test_streamlit_calculator_operations_buttons(self):
48        for key in ('/', 'X', r'\-', r'\+', '=', 'C', 'AC'):
49            with self.subTest(key=key):
50                self.assertEqual(
51                    self.tester.button(key).proto.type,
52                    'primary'
53                )
54
55
56# Exceptions seen

    the terminal_ shows AssertionError

    SUBFAILED(key='C') ... - AssertionError: 'secondary' != 'primary'
SUBFAILED(key='AC') ... - AssertionError: 'secondary' != 'primary'

  • I change the type for the AC button in the add_buttons_to_column_3 function in streamlit_calculator.py

    20def add_buttons_to_column_3(column_3):
21    column_3.button(
22        label='AC', key='AC', width='stretch', type='primary',
23    )
24    column_3.button(label='9', key='9', width='stretch')
25    column_3.button(label='6', key='6', width='stretch')
26    column_3.button(label='3', key='3', width='stretch')
27    column_3.button(label='.', key='.', width='stretch')

    the terminal_ shows AssertionError

    SUBFAILED(key='C') ... - AssertionError: 'secondary' != 'primary'

  • I change the type for the C button in the add_buttons_to_column_2 function

    12def add_buttons_to_column_2(column_2):
13    column_2.button(
14        label='C', key='C', width='stretch', type='primary',
15    )
16    column_2.button(label='8', key='8', width='stretch')
17    column_2.button(label='5', key='5', width='stretch')
18    column_2.button(label='2', key='2', width='stretch')
19    column_2.button(label='0', key='0', width='stretch')

    the test passes

  • I check the browser

    Calculator Streamlit Primary Buttons

    much better

how to show the numbers when I click on them

I want the calculator to show the number when I press a button

  • I add a variable to name the container so I can use it to show the numbers

    50def main():
51    streamlit.title('Calculator')
52    display = streamlit.container(border=True)
53
54    column_1, column_2, column_3, operations = streamlit.columns(4)
55    add_buttons_to_column_1(column_1)
56    add_buttons_to_column_2(column_2)
57    add_buttons_to_column_3(column_3)
58    add_buttons_to_column_4(operations)

  • I add a function to show the text of the button when it is clicked

    1import streamlit
2
3
4def show(display, number):
5    display.write(number)
6
7
8def add_buttons_to_column_1(column_1):

  • `streamlit buttons`_ have an on_click parameter that lets me call a function when a button is pressed. It also takes an argument named args where I can pass in the positional arguments that the function I give for the on_click parameter takes. I pass the function and the display variable with a value as the arguments for the 7 button in the add_buttons_to_column_1 function

     8def add_buttons_to_column_1(column_1):
 9    column_1.button(label='<-', key='<-', width='stretch')
10    column_1.button(
11        label='7', key='7', width='stretch',
12        on_click=show, args=[display, '7'],
13    )
14    column_1.button(label='4', key='4', width='stretch')
15    column_1.button(label='1', key='1', width='stretch')
16    column_1.button(label='+/-', key='+/-', width='stretch')

    the terminal_ shows KeyError

    ================== 26 failed, 12 passed in A.BCs ===================

    the terminal_ for the application shows NameError

    NameError: name 'display' is not defined

  • I add a parameter for the display variable in the function signature for add_buttons_to_column_1

    8def add_buttons_to_column_1(column_1, display):

    the terminal_ shows KeyError for 27 sub tests and the terminal_ for the streamlit_ application shows TypeError

    TypeError: add_buttons_to_column_1() missing 1 required positional argument: 'display'

  • I add the display variable to the call to add_buttons_to_column_1 in the main function

    57def main():
58    streamlit.title('Calculator')
59    display = streamlit.container(border=True)
60
61    column_1, column_2, column_3, operations = streamlit.columns(4)
62    add_buttons_to_column_1(column_1, display)
63    add_buttons_to_column_2(column_2)
64    add_buttons_to_column_3(column_3)
65    add_buttons_to_column_4(operations)

    the test passes

  • I go to the browser and click on the 7 button

    Calculator Streamlit Display 7 on click

    7 shows on the display. Yes!

  • I make the same change to the other numbers in the first column

     8def add_buttons_to_column_1(column_1, display):
 9    column_1.button(label='<-', key='<-', width='stretch')
10    column_1.button(
11        label='7', key='7', width='stretch',
12        on_click=show, args=[display, '7'],
13    )
14    column_1.button(
15        label='4', key='4', width='stretch',
16        on_click=show, args=[display, '4']
17    )
18    column_1.button(
19        label='1', key='1', width='stretch',
20        on_click=show, args=[display, '1']
21    )
22    column_1.button(
23        label='+/-', key='+/-', width='stretch',
24        on_click=show, args=[display, '+/-']
25    )

    the test is still green

  • I do the same thing for the numbers in the second column

    28def add_buttons_to_column_2(column_2):
29    column_2.button(
30        label='C', key='C', width='stretch', type='primary',
31    )
32    column_2.button(
33        label='8', key='8', width='stretch',
34        on_click=show, args=[display, '8']
35    )
36    column_2.button(
37        label='5', key='5', width='stretch',
38        on_click=show, args=[display, '5']
39    )
40    column_2.button(
41        label='2', key='2', width='stretch',
42        on_click=show, args=[display, '2']
43    )
44    column_2.button(
45        label='0', key='0', width='stretch',
46        on_click=show, args=[display, '0']
47    )

    the terminal_ shows KeyError for 20 sub tests and the terminal_ for the application shows NameError

  • I add display to the function signature of the add_buttons_to_column_2 function

    28def add_buttons_to_column_2(column_2, display):

    the terminal_ shows KeyError for 22 sub tests and the terminal_ for the application shows TypeError

    TypeError: add_buttons_to_column_2() missing 1 required positional argument: 'display'

  • I add display to the call to the add_buttons_to_column_2 function in the main function

    78def main():
79    streamlit.title('Calculator')
80    display = streamlit.container(border=True)
81
82    column_1, column_2, column_3, operations = streamlit.columns(4)
83    add_buttons_to_column_1(column_1, display)
84    add_buttons_to_column_2(column_2, display)
85    add_buttons_to_column_3(column_3)
86    add_buttons_to_column_4(operations)

    the test passes

  • I make the same change for the numbers in the third column

    47def add_buttons_to_column_3(column_3):
48    column_3.button(
49        label='AC', key='AC', width='stretch', type='primary',
50    )
51    column_3.button(
52        label='9', key='9', width='stretch',
53        on_click=show, args=[display, '9'],
54    )
55    column_3.button(
56        label='6', key='6', width='stretch',
57        on_click=show, args=[display, '6'],
58    )
59    column_3.button(
60        label='3', key='3', width='stretch',
61        on_click=show, args=[display, '3'],
62    )
63    column_3.button(
64        label='.', key='.', width='stretch',
65        on_click=show, args=[display, '.'],
66    )

    green

  • I go to the browser to test the numbers and they show up in the box, with one problem - every time I press a button it shows a new number. I want the numbers to stay so that I can make numbers that have more than one digit

close the project

review

I now have three different versions of the same calculator:

  • Pure Python (chapters 1–8)

  • Flask website (chapter 9)

  • Streamlit web app (chapter 10) — the fastest and most beautiful version

The core calculator code never changed. All my tests still protect it. This is the real power of Test-Driven Development.

code from the chapter

Do you want to see all the CODE I typed in this chapter?

what is next?

You have completed an amazing journey from pure functions to real web applications!

You now know how to:

  • Build programs with Test-Driven Development

  • Turn them into Flask websites

  • Turn them into beautiful Streamlit apps

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