how to make a calculator 5

I want to practice using lists with the calculator project

preview

These are the tests I have by the end of the chapter

open the project

  • I change directory to the calculator folder

    cd calculator

    the terminal shows I am in the calculator folder

    .../pumping_python/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 5 items

tests/test_calculator.py .....                                [100%]

======================== 5 passed in X.YZs =========================

  • I hold ctrl on the keyboard, then click on tests/test_calculator.py to open it in the editor

test_calculator_sends_message_when_input_is_a_list

I want to see what happens when I send a list as input to the calculator program, will it send a message or raise TypeError?

RED: make it fail

I add a test to see what happens when I send a list as input

 88        self.assertEqual(
 89            src.calculator.subtract('1', '1'),
 90            error_message
 91        )
 92
 93    def test_calculator_sends_message_when_input_is_a_list(self):
 94        a_list = [0, 1, 2, 3]
 95
 96        self.assertEqual(
 97            src.calculator.add(a_list, 0),
 98            'BOOM!!!'
 99        )
100
101
102# Exceptions seen

the terminal shows AssertionError

AssertionError: 'brmph?! Numbers only. Try again...' != 'BOOM!!!'

GREEN: make it pass

I change the expectation to match

96        self.assertEqual(
97            src.calculator.add(a_list, 0),
98            'brmph?! Numbers only. Try again...'
99        )

the test passes

REFACTOR: make it better

  • I add another assertion for the next function

     93    def test_calculator_sends_message_when_input_is_a_list(self):
 94        a_list = [0, 1, 2, 3]
 95
 96        self.assertEqual(
 97            src.calculator.add(a_list, 0),
 98            'brmph?! Numbers only. Try again...'
 99        )
100        self.assertEqual(
101            src.calculator.divide(a_list, 1),
102            'BAP!!!'
103        )
104
105
106# Exceptions seen

    the terminal shows AssertionError

    AssertionError: 'brmph?! Numbers only. Try again...' != 'BAP!!!'

  • I change the expectation

    101        self.assertEqual(
102            src.calculator.divide(a_list, 1),
103            'brmph?! Numbers only. Try again...'
104        )

    the test passes. Wait a minute! I just wrote the same thing twice, and I did it 8 times before in test_calculator_sends_message_when_input_is_not_a_number and 2 times in the numbers_only function. Never again

  • I add a variable

     93    def test_calculator_sends_message_when_input_is_a_list(self):
 94        a_list = [0, 1, 2, 3]
 95        error_message = 'brmph?! Numbers only. Try again...'
 96
 97        self.assertEqual(
 98            src.calculator.add(a_list, 0),
 99            'brmph?! Numbers only. Try again...'
100        )

  • I use the variable to remove the repetition

     93    def test_calculator_sends_message_when_input_is_a_list(self):
 94        a_list = [0, 1, 2, 3]
 95        error_message = 'brmph?! Numbers only. Try again...'
 96
 97        self.assertEqual(
 98            src.calculator.add(a_list, 0),
 99            error_message
100        )
101        self.assertEqual(
102            src.calculator.divide(a_list, 1),
103            error_message
104        )

    the test is still green

how to multiply a list

  • I add an assertion for the multiply function

    101        self.assertEqual(
102            src.calculator.divide(a_list, 1),
103            error_message
104        )
105        self.assertEqual(
106            src.calculator.multiply(a_list, 2),
107            'BOOM!!!'
108        )
109
110
111# Exceptions seen

    the terminal shows AssertionError

    AssertionError: [0, 1, 2, 3, 0, 1, 2, 3] != 'BOOM!!!'

    oh wow! I now know how to multiply a list

  • I change the expectation of the test to the error message

    105        self.assertEqual(
106            src.calculator.multiply(a_list, 2),
107            error_message
108        )

    the terminal shows AssertionError

    AssertionError: [0, 1, 2, 3, 0, 1, 2, 3, 0, 1, 2, 3] != 'brmph?! Numbers only. Try again...'

  • I open calculator.py in the editor

  • I add an if statement to the multiply function in calculator.py

    19@numbers_only
20def multiply(first_input, second_input):
21    if (
22        isinstance(first_input, list)
23        or
24        isinstance(second_input, list)
25    ):
26        return 'brmph?! Numbers only. Try again...'
27    return first_input * second_input

    the test passes

  • I add an assertion for the subtract function in test_calculator_sends_message_when_input_is_a_list to test_calculator.py

    105        self.assertEqual(
106            src.calculator.multiply(a_list, 2),
107            error_message
108        )
109        self.assertEqual(
110            src.calculator.subtract(a_list, 3),
111            'BOOM!!!'
112        )
113
114
115# Exceptions seen

    the terminal shows AssertionError

    AssertionError: 'brmph?! Numbers only. Try again...' != 'BOOM!!!'

  • I change the expectation to match

     93    def test_calculator_sends_message_when_input_is_a_list(self):
 94        a_list = [0, 1, 2, 3]
 95        error_message = 'brmph?! Numbers only. Try again...'
 96
 97        self.assertEqual(
 98            src.calculator.add(a_list, 0),
 99            error_message
100        )
101        self.assertEqual(
102            src.calculator.divide(a_list, 1),
103            error_message
104        )
105        self.assertEqual(
106            src.calculator.multiply(a_list, 2),
107            error_message
108        )
109        self.assertEqual(
110            src.calculator.subtract(a_list, 3),
111            error_message
112        )
113
114
115# Exceptions seen

    the test passes

  • I remove the name of the test to move the new assertions to test_calculator_sends_message_when_input_is_not_a_number

     84        self.assertEqual(
 85            src.calculator.multiply('1', '1'),
 86            error_message
 87        )
 88        self.assertEqual(
 89            src.calculator.subtract('1', '1'),
 90            error_message
 91        )
 92
 93        a_list = [0, 1, 2, 3]
 94        error_message = 'brmph?! Numbers only. Try again...'
 95
 96        self.assertEqual(
 97            src.calculator.add(a_list, 0),
 98            error_message
 99        )
100        self.assertEqual(
101            src.calculator.divide(a_list, 1),
102            error_message
103        )

    the tests are still green

  • I remove the repetition of the error_message variable

     57    def test_calculator_sends_message_when_input_is_not_a_number(self):
 58        error_message = 'brmph?! Numbers only. Try again...'
 59
 60        self.assertEqual(
 61            src.calculator.add(None, None),
 62            error_message
 63        )
 64        self.assertEqual(
 65            src.calculator.divide(None, None),
 66            error_message
 67        )
 68        self.assertEqual(
 69            src.calculator.multiply(None, None),
 70            error_message
 71        )
 72        self.assertEqual(
 73            src.calculator.subtract(None, None),
 74            error_message
 75        )
 76        self.assertEqual(
 77            src.calculator.add('1', '1'),
 78            error_message
 79        )
 80        self.assertEqual(
 81            src.calculator.divide('1', '1'),
 82            error_message
 83        )
 84        self.assertEqual(
 85            src.calculator.multiply('1', '1'),
 86            error_message
 87        )
 88        self.assertEqual(
 89            src.calculator.subtract('1', '1'),
 90            error_message
 91        )
 92
 93        a_list = [0, 1, 2, 3]
 94
 95        self.assertEqual(
 96            src.calculator.add(a_list, 0),
 97            error_message
 98        )
 99        self.assertEqual(
100            src.calculator.divide(a_list, 1),
101            error_message
102        )
103        self.assertEqual(
104            src.calculator.multiply(a_list, 2),
105            error_message
106        )
107        self.assertEqual(
108            src.calculator.subtract(a_list, 3),
109            error_message
110        )
111
112
113# Exceptions seen

    still green. test_calculator_sends_message_when_input_is_not_a_number is getting long, there has to be a better way to test the calculator with inputs that are NOT numbers

test_calculator_w_list_items

I can use a list to test the calculator functions as long as its items are numbers

RED: make it fail

I add a new test to use the index of the items in the list to test the calculator

107          self.assertEqual(
108              src.calculator.subtract(a_list, 3),
109              error_message
110          )
111
112      def test_calculator_w_list_items(self):
113          two_numbers = [
114              self.random_first_number,
115              self.random_second_number
116          ]
117
118          self.assertEqual(
119              src.calculator.add(
120                  two_numbers[0],
121                  two_numbers[1]
122              ),
123              self.random_first_number-self.random_second_number
124          )
125
126
127  # Exceptions seen

the terminal shows AssertionError

AssertionError: ABC.DEFGHIJKLMNOPQ != RST.UVWXYZABCDEFG

GREEN: make it pass

I change the expectation to the right calculation

118          self.assertEqual(
119              src.calculator.add(
120                  two_numbers[0],
121                  two_numbers[1]
122              ),
123              self.random_first_number+self.random_second_number
124          )

the test passes. two_numbers is a list with two items - self.random_first_number and self.random_second_number, this means

  • two_numbers[0] is self.random_first_number

  • two_numbers[1] is self.random_second_number

REFACTOR: make it better

  • I add an assertion for the divide function

    118        self.assertEqual(
119            src.calculator.add(
120                two_numbers[0],
121                two_numbers[1]
122            ),
123            self.random_first_number+self.random_second_number
124        )
125        self.assertEqual(
126            src.calculator.divide(
127                two_numbers[-2],
128                two_numbers[-1]
129            ),
130            self.random_first_number*self.random_second_number
131        )

    the terminal shows AssertionError

    AssertionError: D.EFGHIJKLMNOPQRST != UVWXY.ZABCDEFGHIJ

  • I change the calculation to division

    125        self.assertEqual(
126            src.calculator.divide(
127                two_numbers[-2],
128                two_numbers[-1]
129            ),
130            self.random_first_number/self.random_second_number
131        )

    the test passes. two_numbers is a list with two items - self.random_first_number and self.random_second_number, this means

  • two_numbers[-2] is self.random_first_number

  • two_numbers[-1] is self.random_second_number

  • I add an assertion for multiplication

    125        self.assertEqual(
126            src.calculator.divide(
127                two_numbers[-2],
128                two_numbers[-1]
129            ),
130            self.random_first_number/self.random_second_number
131        )
132        self.assertEqual(
133            src.calculator.multiply(
134                two_numbers[1],
135                two_numbers[-1]
136            ),
137            self.random_first_number*self.random_second_number
138        )

    the terminal shows AssertionError

    AssertionError: EFGHIJ.KLMNOPQRSTU != VWXYZ.ABCDEFGHIJKL

  • I change the expectation

    132        self.assertEqual(
133            src.calculator.multiply(
134                two_numbers[1],
135                two_numbers[-1]
136            ),
137            self.random_second_number*self.random_second_number
138        )

    the test passes. two_numbers is a list with two items - self.random_first_number and self.random_second_number, this means

  • two_numbers[1] is self.random_second_number

  • two_numbers[-1] is self.random_second_number

  • I add an assertion for the subtract function

    132        self.assertEqual(
133            src.calculator.multiply(
134                two_numbers[1],
135                two_numbers[-1]
136            ),
137            self.random_second_number*self.random_second_number
138        )
139        self.assertEqual(
140            src.calculator.subtract(
141                two_numbers[-2],
142                two_numbers[0]
143            ),
144            self.random_first_number-self.random_second_number
145        )

    the terminal shows AssertionError

    AssertionError: 0.0 != FGH.IJKLMNOPQRSTU

  • I change the expectation to match

    139        self.assertEqual(
140            src.calculator.subtract(
141                two_numbers[-2],
142                two_numbers[0]
143            ),
144            self.random_first_number-self.random_first_number
145        )
146
147
148# Exceptions seen

    the test passes. two_numbers is a list with two items - self.random_first_number and self.random_second_number, this means

  • two_numbers[-2] is self.random_first_number

  • two_numbers[0] is self.random_first_number

test calculator with * expression

RED: make it fail

I can use a starred expression to unpack the list in an assertion like the positional arguments in test_functions_w_unknown_arguments

139      self.assertEqual(
140          src.calculator.subtract(
141              two_numbers[-2],
142              two_numbers[0]
143          ),
144          self.random_first_number-self.random_first_number
145      )
146      self.assertEqual(
147          src.calculator.add(*two_numbers),
148          self.random_first_number-self.random_second_number
149      )

the terminal shows AssertionError

AssertionError: GHI.JKLMNOPQRSTUVW != XYZ.ABCDEFGHIJKLMN

GREEN: make it pass

I change the expectation to match the result of adding the two numbers from the list

146        self.assertEqual(
147            src.calculator.add(*two_numbers),
148            self.random_first_number+self.random_second_number
149        )

the test passes. The starred expression gives the items of the list in the same order every time, this means these statements are the same

src.calculator.add(*two_numbers)
src.calculator.add(self.random_first_number, self.random_second_number)

because two_numbers is a list with two items - self.random_first_number and self.random_second_number

REFACTOR: make it better

  • I add another assertion for division

    146        self.assertEqual(
147            src.calculator.add(*two_numbers),
148            self.random_first_number+self.random_second_number
149        )
150        self.assertEqual(
151            src.calculator.divide(*two_numbers),
152            self.random_first_number*self.random_second_number
153        )

    the terminal shows AssertionError

    AssertionError: H.IJKLMNOPQRSTUVWX != YZABCD.EFGHIJKLMNO

  • I change the calculation

    150        self.assertEqual(
151            src.calculator.divide(*two_numbers),
152            self.random_first_number/self.random_second_number
153        )

    the test passes

  • I add an assertion for the multiply function

    150        self.assertEqual(
151            src.calculator.divide(*two_numbers),
152            self.random_first_number/self.random_second_number
153        )
154        self.assertEqual(
155            src.calculator.multiply(*two_numbers),
156            self.random_first_number/self.random_second_number
157        )

    the terminal shows AssertionError

    AssertionError: IJKLMN.OPQRSTUVWX != Y.ZABCDEFGHIJKLMNOP

  • I change the calculation in the expectation to multiplication

    154        self.assertEqual(
155            src.calculator.multiply(*two_numbers),
156            self.random_first_number*self.random_second_number
157        )

    the test passes

  • I add the next assertion

    154        self.assertEqual(
155            src.calculator.multiply(*two_numbers),
156            self.random_first_number*self.random_second_number
157        )
158        self.assertEqual(
159            src.calculator.subtract(*two_numbers),
160            self.random_first_number+self.random_second_number
161        )

    the terminal shows AssertionError

    AssertionError: JKL.MNOPQRSTUVWXYZ != ABC.DEFGHIJKLMNOP

  • I change the expectation to subtraction

    112    def test_calculator_w_list_items(self):
113        two_numbers = [
114            self.random_first_number,
115            self.random_second_number
116        ]
117
118        self.assertEqual(
119            src.calculator.add(
120                two_numbers[0],
121                two_numbers[1]
122            ),
123            self.random_first_number+self.random_second_number
124        )
125        self.assertEqual(
126            src.calculator.divide(
127                two_numbers[-2],
128                two_numbers[-1]
129            ),
130            self.random_first_number/self.random_second_number
131        )
132        self.assertEqual(
133            src.calculator.multiply(
134                two_numbers[1],
135                two_numbers[-1]
136            ),
137            self.random_second_number*self.random_second_number
138        )
139        self.assertEqual(
140            src.calculator.subtract(
141                two_numbers[-2],
142                two_numbers[0]
143            ),
144            self.random_first_number-self.random_first_number
145        )
146        self.assertEqual(
147            src.calculator.add(*two_numbers),
148            self.random_first_number+self.random_second_number
149        )
150        self.assertEqual(
151            src.calculator.divide(*two_numbers),
152            self.random_first_number/self.random_second_number
153        )
154        self.assertEqual(
155            src.calculator.multiply(*two_numbers),
156            self.random_first_number*self.random_second_number
157        )
158        self.assertEqual(
159            src.calculator.subtract(*two_numbers),
160            self.random_first_number-self.random_second_number
161        )
162
163
164# Exceptions seen

    the test passes

test_calculator_raises_type_error_when_given_more_than_two_inputs

It is important to remember that the starred expression always gives the items from the list in order, and I cannot use a list that has more than 2 numbers with these calculator functions since they only take 2 inputs

RED: make it fail

I add a new test to show the problem when I have more than 2 inputs and use a starred expression

158        self.assertEqual(
159            src.calculator.subtract(*two_numbers),
160            self.random_first_number-self.random_second_number
161        )
162
163    def test_calculator_raises_type_error_when_given_more_than_two_inputs(self):
164        not_two_numbers = [0, 1, 2]
165
166        src.calculator.add(*not_two_numbers)
167
168
169# Exceptions seen

the terminal shows TypeError

TypeError: numbers_only.<locals>.wrapper() takes 2 positional arguments but 3 were given

GREEN: make it pass

I add the assertRaises method to handle the Exception

163    def test_calculator_raises_type_error_when_given_more_than_two_inputs(self):
164        not_two_numbers = [0, 1, 2]
165
166        with self.assertRaises(TypeError):
167            src.calculator.add(*not_two_numbers)

the test passes

REFACTOR: make it better

  • I add a failing line for division with the new list

    163    def test_calculator_raises_type_error_when_given_more_than_two_inputs(self):
164        not_two_numbers = [0, 1, 2]
165
166        with self.assertRaises(TypeError):
167            src.calculator.add(*not_two_numbers)
168        src.calculator.divide(*not_two_numbers)

    the terminal shows TypeError

    TypeError: numbers_only.<locals>.wrapper() takes 2 positional arguments but 3 were given

  • I add assertRaises

    166        with self.assertRaises(TypeError):
167            src.calculator.add(*not_two_numbers)
168        with self.assertRaises(TypeError):
169            src.calculator.divide(*not_two_numbers)

    the test passes

  • I add a line for multiplication

    168        with self.assertRaises(TypeError):
169            src.calculator.divide(*not_two_numbers)
170        src.calculator.multiply(*not_two_numbers)

    the terminal shows TypeError

    TypeError: numbers_only.<locals>.wrapper() takes 2 positional arguments but 3 were given

  • I add assertRaises

    168        with self.assertRaises(TypeError):
169            src.calculator.divide(*not_two_numbers)
170        with self.assertRaises(TypeError):
171            src.calculator.multiply(*not_two_numbers)

    the test passes

  • I add the last line

    170        with self.assertRaises(TypeError):
171            src.calculator.multiply(*not_two_numbers)
172        src.calculator.subtract(*not_two_numbers)

    the terminal shows TypeError

    TypeError: numbers_only.<locals>.wrapper() takes 2 positional arguments but 3 were given

  • I handle the Exception

    163    def test_calculator_raises_type_error_when_given_more_than_two_inputs(self):
164        not_two_numbers = [0, 1, 2]
165
166        with self.assertRaises(TypeError):
167            src.calculator.add(*not_two_numbers)
168        with self.assertRaises(TypeError):
169            src.calculator.divide(*not_two_numbers)
170        with self.assertRaises(TypeError):
171            src.calculator.multiply(*not_two_numbers)
172        with self.assertRaises(TypeError):
173            src.calculator.subtract(*not_two_numbers)
174
175
176# Exceptions seen

    the test passes

close the project

  • I close test_calculator.py and calculator.py in the editors

  • I click in the terminal, then use q on the keyboard to leave the tests. The terminal goes back to the command line

  • I change directory to the parent of calculator

    cd ..

    the terminal shows

    .../pumping_python

    I am back in the pumping_python directory

review

I added these tests to the calculator program after testing lists

code from the chapter

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

what is next?

you know

would you like to test list comprehensions? They are a quick way to make lists

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