TypeError¶

The TypeError is raised when an object is used in a way that it should not be.

test_type_error_w_non_callables ¶

There are objects that cannot be called

red: make it fail¶

I open a terminal to run makePythonTdd.sh with type_error as the name of the project
```
./makePythonTdd.sh type_error
```
on Windows without Windows Subsystem Linux use makePythonTdd.ps1
```
./makePythonTdd.ps1 type_error
```
it makes the folders and files that are needed, installs packages, runs the first test, and the terminal shows AssertionError
```
E       AssertionError: True is not false

tests/test_type_error.py:7: AssertionError
```
I hold ctrl (windows/linux) or option (mac) on the keyboard and use the mouse to click on tests/test_type_error.py:7 to open it in the editor
then change True to False
I add an import statement
```
import unittest
import src.type_error
```

and change test_failure to test_type_error_w_non_callables

class TestTypeError(unittest.TestCase):

    def test_type_error_w_non_callables(self):
        src.type_error.none()

the terminal shows AttributeError

AttributeError: module 'src.type_error' has no attribute 'none'

I add it to the list of Exceptions encountered

# Exceptions Encountered
# AssertionError
# AttributeError

green: make it pass¶

then I add the name to type_error.py and point it to None
```
none = None
```
the terminal shows TypeError
```
TypeError: 'NoneType' object is not callable
```
the () to the right of src.type_error.none makes it a call, and the name none is a reference to None which is not callable

I add the error to the list of Exceptions encountered

# Exceptions Encountered
# AssertionError
# AttributeError
# TypeError

and I make none a function to make it callable
```
def none():
    return None
```
the test passes

refactor: make it better¶

I add another line to the test

def test_type_error_w_non_callables(self):
    src.type_error.none()
    src.type_error.false()

and the terminal shows AttributeError

AttributeError: module 'src.type_error' has no attribute 'false'

when I add the name to type_error.py and point it to False

def none():
    return None


false = False

the terminal shows TypeError

TypeError: 'bool' object is not callable

I make it a function

def none():
    return None

def false():
    return False

and the terminal shows green again

I add a line to test the other boolean

def test_type_error_w_non_callables(self):
    src.type_error.none()
    src.type_error.false()
    src.type_error.true()

the terminal shows AttributeError

AttributeError: module 'src.type_error' has no attribute 'true'

I add the name to type_error.py and point it to True

def false():
    return False


true = True

and get TypeError

TypeError: 'bool' object is not callable

when I make it a function

def false():
    return False


def true():
    return True

the test passes

I add another line to the test

def test_type_error_w_non_callables(self):
    src.type_error.none()
    src.type_error.false()
    src.type_error.true()
    src.type_error.a_list()

and the terminal shows AttributeError

AttributeError: module 'src.type_error' has no attribute 'a_list'

I add the name and point it to a list

def true():
    return True


a_list = [1, 2, 3, 'n']

and the terminal shows TypeError

TypeError: 'list' object is not callable

then I make it a function

def true():
    return True


def a_list():
    return [1, 2, 3, 'n']

and the test passes

I add a new failing line

def test_type_error_w_non_callables(self):
    src.type_error.none()
    src.type_error.false()
    src.type_error.true()
    src.type_error.a_list()
    src.type_error.a_dictionary()

the terminal shows AttributeError

AttributeError: module 'src.type_error' has no attribute 'a_dictionary'

I add the name and point it to a dictionary

def a_list():
    return [1, 2, 3, 'n']


a_dictionary = {'key': 'value'}

and the terminal shows TypeError

TypeError: 'dict' object is not callable

then I change it to a function

def a_list():
    return [1, 2, 3, 'n']


def a_dictionary():
    return {'key': 'value'}

and the terminal shows green again. It is safe to say that I cannot call data structures.

test_type_error_w_function_signatures ¶

Calls to a function have to match its signature

red: make it fail¶

I add a new test

def test_type_error_w_function_signatures(self):
    src.type_error.function_00('a')

the terminal shows AttributeError

AttributeError: module 'src.type_error' has no attribute 'function_00'

then I add the function to type_error.py

def a_dictionary():
    return {'key': 'value'}


def function_00():
    return None

and get TypeError

TypeError: function_00() takes 0 positional arguments but 1 was given

because function_00 is called with 'a' as input but the definition does not accept any inputs

green: make it pass¶

I add an input parameter to the function definition
```
def function_00(argument):
    return None
```
and the terminal shows passing tests

refactor: make it better¶

I add a new failing line

def test_type_error_w_function_signatures(self):
    src.type_error.function_00('a')
    src.type_error.function_01('a', 'b')

the terminal shows AttributeError

AttributeError: module 'src.type_error' has no attribute 'function_01'. Did you mean: 'function_00'?

I add the function

def function_00(argument):
    return None


def function_01(argument):
    return None

and the terminal shows TypeError

TypeError: function_01() takes 1 positional argument but 2 were given

when I make the number of inputs in the definition match the number of inputs in the call

def function_01(
      argument_1, argument_2
  ):
  return None

the test passes

I add another failing line

def test_type_error_w_function_signatures(self):
    src.type_error.function_00('a')
    src.type_error.function_01('a', 'b')
    src.type_error.function_02('a', 'b', 'c')

the terminal shows AttributeError

AttributeError: module 'src.type_error' has no attribute 'function_02'. Did you mean: 'function_00'?

I add the function to type_error.py

def function_01(
        argument_1, argument_2
    ):
    return None


def function_02(
        argument_1, argument_2
    ):
    return None

and the terminal shows TypeError

TypeError: function_02() takes 2 positional arguments but 3 were given

then I make the number of inputs match

def function_02(
        argument_1, argument_2,
        argument_3
    ):
    return None

and the terminal shows green again

I add one more failing line to the test

def test_type_error_w_function_signatures(self):
    src.type_error.function_00('a')
    src.type_error.function_01('a', 'b')
    src.type_error.function_02('a', 'b', 'c')
    src.type_error.function_03('a', 'b', 'c', 'd')

the terminal shows AttributeError

AttributeError: module 'src.type_error' has no attribute 'function_03'. Did you mean: 'function_00'?

I add the function

def function_02(
        argument_1, argument_2,
        argument_3
    ):
    return None


def function_03(
        argument_1, argument_2,
        argument_3
    ):
    return None

and get TypeError

TypeError: function_03() takes 3 positional arguments but 4 were given

I add a 4th parameter to the definition

def function_03(
    argument_1, argument_2,
    argument_3, argument_4
):
    return None

and the terminal shows both tests are passing.

test_type_error_w_objects_that_do_not_mix ¶

Some operations do not work if the objects are not the same type

red: make it fail¶

I add a new test with a failing line

def test_type_error_w_objects_that_do_not_mix(self):
    None + 1

the terminal shows TypeError

TypeError: unsupported operand type(s) for +: 'NoneType' and 'int'

I cannot do arithmetic with None

green: make it pass¶

I add the assertRaises method

def test_type_error_w_objects_that_do_not_mix(self):
    with self.assertRaises(TypeError):
        None + 1

and the test passes

refactor: make it better¶

I add another line

def test_type_error_w_objects_that_do_not_mix(self):
    with self.assertRaises(TypeError):
        None + 1
    'text' + 0.1

which gives me TypeError

TypeError: can only concatenate str (not "float") to str

I cannot add something that is not a string to a string. I add assertRaises

def test_type_error_w_objects_that_do_not_mix(self):
    with self.assertRaises(TypeError):
        None + 1
    with self.assertRaises(TypeError):
        'text' + 0.1

and the test passes

then I add one more line

def test_type_error_w_objects_that_do_not_mix(self):
    with self.assertRaises(TypeError):
        None + 1
    with self.assertRaises(TypeError):
        'text' + 0.1
    (1, 2, 3, 'n') - {1, 2, 3, 'n'}

the terminal shows TypeError

TypeError: unsupported operand type(s) for -: 'tuple' and 'set'

I add assertRaises

def test_type_error_w_objects_that_do_not_mix(self):
    with self.assertRaises(TypeError):
        None + 1
    with self.assertRaises(TypeError):
        'text' + 0.1
    with self.assertRaises(TypeError):
        (1, 2, 3, 'n') - {1, 2, 3, 'n'}

and the terminal shows all tests are passing.

review ¶

I ran tests for TypeError with objects that are not callable, function signatures and objects that do not mix. Would you like to test data structures?

Type Error: tests and solution

TypeError¶

test_type_error_w_non_callables¶

red: make it fail¶

green: make it pass¶

refactor: make it better¶

test_type_error_w_function_signatures¶

red: make it fail¶

green: make it pass¶

refactor: make it better¶

test_type_error_w_objects_that_do_not_mix¶

red: make it fail¶

green: make it pass¶

refactor: make it better¶

review¶

test_type_error_w_non_callables ¶

test_type_error_w_function_signatures ¶

test_type_error_w_objects_that_do_not_mix ¶

review ¶