---

---

---

what causes TypeError?

---

TypeError happens when an object (everything in Python is an object) is used in a way that it should not be.

---

preview

I have these tests by the end of the chapter

type_error/tests/test_type_error.py

def function_00(the_input):
    return None


def function_01(first, second):
    return None


def function_02(first, second, third):
    return None


def function_03(first, second, third, fourth):
    return None

type_error/tests/test_type_error.py

def function_04(argument):
    return None


def function_05(argument_0, argument_1):
    return None


def function_06(
    argument_0, argument_1,
    argument_2,
):
    return None


def function_07(
    argument_0, argument_1,
    argument_2, argument_n,
):
    return None

type_error/tests/test_type_error.py

def function_08(name, argument):
    return None


def test_type_error_w_positional_arguments():
    function_00('a')
    function_01('a', 'b')
    function_02('a', 'b', 'c')
    function_03('a', 'b', 'c', 'd')
    function_04('a')
    function_05('a', 'b')
    function_06('a', 'b', 'c')
    function_07('a', 'b', 'c', 'd')
    function_08('last', 'one')

type_error/tests/test_type_error.py

def test_type_error_w_keyword_arguments():
    function_00(the_input=0)
    function_01(
        first='first',
        second={'key': 'value'},
    )
    function_02(
        third=(0, 1, 2, 'n'),
        second=[0, 1, 2, 'n'],
        first={0, 1, 2, 'n'},
    )
    function_03(
        first=None,
        second=False,
        third=True,
        fourth=4,
    )
    function_04(argument='value')
    function_05(
        argument_0='value_1',
        argument_1=(0, 1, 2, 'n'),
    )
    function_06(
        argument_0='value_1',
        argument_1=(0, 1, 2, 'n'),
        argument_2=[0, 1, 2, 'n'],
    )
    function_07(
        argument_0=(0, 1, 2, 'n'),
        argument_1=[0, 1, 2, 'n'],
        argument_2={0, 1, 2, 'n'},
        argument_n={'key': 'value'},
    )
    function_08(
        argument='positional',
        name='keyword',
    )

type_error/tests/test_type_error.py

def test_type_error_w_args_and_kwargs():
    function_00('argument')
    function_01(1, 0)
    function_02(
        third=True, second=False,
        first=None,
    )
    function_03(
        second=[0, 1, 2, 'n'],
        first=(0, 1, 2, 'n'),
        third={0, 1, 2, 'n'},
        fourth={'key': 'value'},
    )
    function_04(argument='value_2')
    function_05((0, 1, 2, 'n'), [0, 1, 2, 'n'])
    function_06(
        argument_2=(0, 1, 2, 'n'),
        argument_0=[0, 1, 2, 'n'],
        argument_1={0, 1, 2, 'n'},
    )
    function_07(
        argument_n={'key': 'value'},
        argument_2={0, 1, 2, 'n'},
        argument_0=(0, 1, 2, 'n'),
        argument_1=[0, 1, 2, 'n'],
    )
    function_08(
        'positional',
        argument='keyword',
    )


# Exceptions seen
# AssertionError
# NameError
# TypeError

questions about TypeError

• what causes TypeError?

• what happens when I call a function and do not send the right number of inputs?

• what happens when I call a function and do not use the right names?

• what happens when I call a function with multiple values for the same argument?

---

start the project

• I name this project type_error

• I open a terminal

• I change directory to the type_error folder in the pumping_python folder

  terminal

  cd type_error
  

  the terminal shows

  cd: no such file or directory: type_error
  

  there is no folder with the name type_error in this folder.

• I use uv to make a directory for the project and initialize it

  terminal

  uv init type_error
  

  the terminal shows

  Initialized project `type-error`
  at `../pumping_python/type_error`
  

  then goes back to the command line.

• I change directory to the project

  terminal

  cd type_error
  

  the terminal shows I am in the type_error folder

  .../pumping_python/type_error
  

• I make a directory for the tests

  terminal

  mkdir tests
  

  the terminal goes back to the command line.

• I make the tests directory a Python package

  Danger

  use 2 underscores (__) before and after init for __init__.py not _init_.py

  WSL/Linux/Mac

  touch tests/__init__.py
  

  no WSL

  New-Item tests/__init__.py
  

  the terminal goes back to the command line.

• I make an empty file for the tests in the tests folder

  WSL/Linux/Mac

  touch tests/test_type_error.py
  

  no WSL

  New-Item tests/test_type_error.py
  

  the terminal goes back to the command line.

• I open test_type_error.py

• I add the first failing test to test_type_error.py

  def test_failure():
      assert False is True
  

• I go back to the terminal

WSL/Linux/Mac

• I use echo to add pytest to requirements.txt

  echo "pytest" > requirements.txt
  

• I add pytest-watcher to the requirements file

  echo "pytest-watcher" >> requirements.txt
  

  the terminal goes back to the command line.

no WSL

• I use Out-File to add pytest to requirements.txt

  "pytest" | Out-File requirements.txt -Encoding UTF8
  

• I add pytest-watcher to the requirements file

  "pytest-watcher" >> requirements.txt
  

• I use uv to install pytest-watcher with the requirements file

  terminal

  uv add --requirement requirements.txt
  

  the terminal shows that it installed pytest-watcher and its dependencies.

• I add the new files and folder to git for tracking

  terminal

  git add .
  

  the terminal goes back to the command line.

• I add a git commit message

  terminal

  git commit --all --message 'setup project'
  

  the terminal shows a summary of the changes then goes back to the command line.

• I use pytest-watcher to run the tests automatically

  terminal

  uv run pytest-watcher . --now --patterns "**/*.py"
  

  the terminal is my friend, and shows AssertionError

  ========================== ERRORS ==========================
  ______ ERROR collecting tests/test_type_error.py ______
  tests/test_type_error.py:2: in <module>
      assert False is True
  E   assert False is True
  ================= short test summary info ==================
  ERROR tests/test_type_error.py - assert False is True
  !!!!!!!!!! Interrupted: 1 error during collection !!!!!!!!!!
  ===================== 1 error in L.MNs =====================
  

  because False is NOT True.

  if the terminal does not show the same error, then check if

  • your tests/__init__.py has two underscores (__) before and after init for __init__.py not _init_.py

  • you ran echo "pytest-watcher" >> requirements.txt, to add pytest-watcher to the requirements file

  and try uv run pytest-watcher . --now --patterns "**/*.py" again

• I add AssertionError to the list of Exceptions seen, in test_type_error.py

  def test_failure():
      assert False is True
  
  
  # Exceptions seen
  # AssertionError
  

• I change False to True in the assertion

  def test_failure():
      # assert False is True
      assert True is True
  
  
  # Exceptions seen
  # AssertionError
  

  the test passes.

---

test_type_error_w_positional_arguments

TypeError happens when I call a function in a way that is different from its signature. I have to match the number of arguments in the function definition when I call the function with positional arguments.

---

RED: make it fail

---

• I change test_failure to test_type_error_w_positional_arguments

  def test_type_error_w_positional_arguments():
      function_00('a')
  
  
  # Exceptions seen
  # AssertionError
  

  the terminal is my friend, and shows NameError

  NameError: name 'function_00' is not defined
  

  because there is nothing named function_00 in test_type_error.py.

• I add NameError to the list of Exceptions seen

---

GREEN: make it pass

---

• I add a definition for the function

  def test_type_error_w_positional_arguments():
      def function_00():
          return None
  
      function_00('a')
  
  
  # Exceptions seen
  

  the terminal is my friend, and shows TypeError

  TypeError:
      test_type_error_w_positional_arguments
          .<locals>.function_00()
      takes 0 positional arguments but 1 was given
  

  because

  • the call to function_00 which belongs to test_type_error_w_positional_arguments used one input ('a').

  • the function definition (signature) of function_00 does not allow any inputs when it is called since the parentheses are empty.

  • the call to a function must match its signature (definition).

• I add TypeError to the list of Exceptions seen

• I add a name in parentheses to the function definition

  def test_type_error_w_positional_arguments():
      # def function_00():
      def function_00(the_input):
          return None
  
      function_00('a')
  
  
  # Exceptions seen
  

  the test passes because the call to the function matches its definition.

---

REFACTOR: make it better

---

• I add a call to function_01

  def test_type_error_w_positional_arguments():
      # def function_00():
      def function_00(the_input):
          return None
  
      function_00('a')
  
      function_01('a', 'b')
  
  
  # Exceptions seen
  

  the terminal is my friend, and shows NameError

  NameError: name 'function_01' is not defined
  

  because there is nothing named function_01 in test_type_error.py.

• I add a definition for function_01

  the terminal is my friend, and shows TypeError

  TypeError:
      test_type_error_w_positional_arguments
          .<locals>.function_01()
      takes 1 positional argument but 2 were given
  

  because

  • the call to function_01 which belongs to test_type_error_w_positional_arguments uses two positional_arguments ('a' and 'b').

  • the function definition (signature) of function_01 only allows one input.

  • the call to a function must match its signature (definition).

• I change the name of the first input, then add another name in parentheses so that the call to the function and its definition match

  the test passes because the call to the function matches its definition.

• I add a call to function_02

  the terminal is my friend, and shows NameError

  NameError: name 'function_02' is not defined
  

  because there is nothing named function_02 in test_type_error.py.

• I add a definition for function_02

  the terminal is my friend, and shows TypeError

  TypeError:
      test_type_error_w_positional_arguments
          .<locals>.function_02()
      takes 2 positional arguments but 3 were given
  

  because

  • the call to function_02 which belongs to test_type_error_w_positional_arguments uses three positional arguments ('a', 'b' and 'c').

  • the function definition (signature) of function_02 only allows two inputs.

  • the call to a function must match its signature (definition).

• I add a third name in parentheses so that the call to function_02 and its definition match

  the test passes because the call to the function matches its definition.

• I add a call to function_03

  the terminal is my friend, and shows NameError

  NameError: name 'function_03' is not defined
  

  because there is nothing named function_03 in test_type_error.py.

• I add a definition for function_03

  the terminal is my friend, and shows TypeError

  TypeError:
      test_type_error_w_positional_arguments
          .<locals>.function_03()
      takes 3 positional arguments but 4 were given
  

  because

  • the call to function_03 which belongs to test_type_error_w_positional_arguments uses four positional arguments ('a', 'b', 'c', 'd').

  • the function definition (signature) of function_03 only allows three inputs.

  • the call to a function must match its signature (definition).

• I add a fourth name in parentheses so that the call to function_03 and its definition match

  the test passes because the call to the function matches its definition.

• I remove the commented lines from test_type_error_w_positional_arguments

  def test_type_error_w_positional_arguments():
      def function_00(the_input):
          return None
  
      function_00('a')
  

• I open a new terminal then change directories to type_error

  terminal

  cd type_error
  

• I add a git commit message in the new terminal

  terminal

  git commit --all --message \
  'add test_type_error_w_positional_arguments'
  

  the terminal shows a summary of the changes then goes back to the command line.

I have to call a function with the same number of inputs that are in its definition.

---

test_type_error_w_keyword_arguments

TypeError happens when I call a function in a way that is different from its signature. I have to match the names of arguments in the function definition when I call the function with keyword arguments.

---

RED: make it fail

---

• I go back to the terminal where the tests are running

• I add a test with a call to function_04 with a keyword argument

  the terminal is my friend, and shows NameError

  NameError: name 'function_04' is not defined
  

  because there is nothing named function_04 in test_type_error.py.

---

GREEN: make it pass

---

• I add a definition for function_04

  the terminal is my friend, and shows TypeError

  TypeError:
      test_type_error_w_keyword_arguments
          .<locals>.function_04()
          got an unexpected keyword argument 'argument'
  

  because

  • the call to function_04 which belongs to test_type_error_w_keyword_arguments uses a keyword argument (argument='value').

  • the function definition (signature) of function_04 does not allow any inputs since the parentheses are empty.

  • the call uses a name (argument) that is not in the parentheses of its definition.

  • the call to a function must match its signature (definition).

• I add argument in the parentheses so that the call to function_04 and its definition match

  the test passes because the call to the function matches its definition.

---

REFACTOR: make it better

---

• I add a call to function_05 with keyword arguments

  the terminal is my friend, and shows NameError

  NameError: name 'function_05' is not defined
  

• I add a definition for function_05

  the terminal is my friend, and shows TypeError

  TypeError:
      test_type_error_w_keyword_arguments
          .<locals>.function_05()
      got an unexpected keyword argument 'argument_0'.
      Did you mean 'argument'?
  

  because

  • the call to function_05 which belongs to test_type_error_w_keyword_arguments uses keyword arguments (argument_0='value_1' and argument_1=(0, 1, 2, 'n')).

  • the function definition (signature) of function_05 only allows one input, with the name argument.

  • the call uses a name (argument_0) that is not in the parentheses of its definition.

  • the call to a function must match its signature (definition).

• I change the name of the input in the definition to match the call

  the terminal shows TypeError

  TypeError:
      test_type_error_w_keyword_arguments
          .<locals>.function_05()
      got an unexpected keyword argument 'argument_1'.
      Did you mean 'argument_0'?
  

  because the call uses a name (argument_1) that is not in the parentheses of its definition.

• I add argument_1 to the parentheses so that the call to function_05 and its definition match

  the test passes because the call to the function matches its definition.

• I add a call to function_06 with keyword arguments

  the terminal is my friend, and shows NameError

  NameError: name 'function_06' is not defined
  

• I add a definition for function_06

  the terminal is my friend, and shows TypeError

  TypeError:
      test_type_error_w_keyword_arguments
          .<locals>.function_06()
      got an unexpected keyword argument 'argument_2'.
      Did you mean 'argument_0'?
  

  because

  • the call to function_06 which belongs to test_type_error_w_keyword_arguments uses keyword arguments (argument_0='value_1', argument_1=(0, 1, 2, 'n') and argument_2=[0, 1, 2, 'n']).

  • the function definition (signature) of function_06 only allows two inputs.

  • the call uses a name (argument_2) that is not in the parentheses of its definition.

  • the call to a function must match its signature (definition).

• I add argument_2 to the parentheses so that the call to function_06 and its definition match

  the test passes because the call to the function matches its definition.

• I add a call to function_07 with keyword arguments

  the terminal is my friend, and shows NameError

  NameError: name 'function_07' is not defined
  

• I add a definition for function_07

  the terminal is my friend, and shows TypeError

  TypeError:
      test_type_error_w_keyword_arguments
          .<locals>.function_07()
      got an unexpected keyword argument 'argument_n'.
      Did you mean 'argument_0'?
  

  because

  • the call to function_07 which belongs to test_type_error_w_keyword_arguments uses keyword arguments (argument_0=(0, 1, 2, 'n'), argument_1=[0, 1, 2, 'n'], argument_2={0, 1, 2, 'n'} and argument_n={'key': 'value'}).

  • the function definition (signature) of function_07 only allows three inputs.

  • the call uses a name (argument_n) that is not in the parentheses of its definition.

  • the call to a function must match its signature (definition).

• I add argument_n to the parentheses so that the call to function_07 and its definition match

  the test passes because the call to the function matches its definition.

• I remove the commented lines from test_type_error_w_keyword_arguments

• I add a git commit message in the other terminal

  terminal

  git commit --all --message \
  'add test_type_error_w_keyword_arguments'
  

  the terminal shows a summary of the changes then goes back to the command line.

If I call a function with keyword arguments, I have to use the same names that are in its definition.

---

test_type_error_w_args_and_kwargs

TypeError happens when I call a function in a way that is different from its signature. I cannot give two values for the same argument in the function definition when I call a function.

---

RED: make it fail

---

• I go back to the terminal where the tests are running

• I add a test with a call to function_08 with a positional and keyword argument

  the terminal is my friend, and shows NameError

  NameError: name 'function_08' is not defined
  

  because there is no definition for function_08 in the file.

---

GREEN: make it pass

---

• I add a function definition for function_08

  the terminal is my friend, and shows TypeError

  TypeError:
      test_type_error_w_args_and_kwargs
          .<locals>.function_08()
      got multiple values for argument 'argument'
  

  because

  • the call to function_08 which belongs to test_type_error_w_args_and_kwargs uses positional and keyword arguments ('positional' and argument='keyword').

  • the function definition (signature) of function_08 takes one argument (argument). How does Python know which value to use for argument if I use the position and the name?

  • the call to a function must match its signature (definition).

• I add another name to the parentheses

  the terminal still shows TypeError because the call gives 'positional' as the value for the first argument which is argument in the definition, and it gives 'keyword' as the value for argument as a keyword argument.

• I change the order of the names in the parentheses of the function definition

  the test passes because the call to the function matches its definition.

---

REFACTOR: make it better

---

• I add another call to function_08

  the terminal is my friend, and shows TypeError

  TypeError:
      test_type_error_w_args_and_kwargs
          .<locals>.function_08()
      got multiple values for argument 'name'
  

  because

  • the call to function_08 which belongs to test_type_error_w_args_and_kwargs uses 'positional' as the value for the first argument which is name in the definition, and uses 'keyword' as the value for name as a keyword argument.

  • the function definition (signature) of function_08 takes two arguments (name and argument). How does Python know which value to use for name if I use the position and the name?

• I use keyword arguments to make the call clearer

  the test passes because the call to the function matches its definition.

• I add a call to function_01 with a positional and keyword argument

  the terminal is my friend, and shows NameError

  NameError: name 'function_01' is not defined
  

  because function_01 belongs to the test_type_error_w_positional_arguments function and I cannot reach it from outside test_type_error_w_positional_arguments.

• I move function_01 out of test_type_error_w_positional_arguments so that it can be called from anywhere in the file

  def function_01(first, second):
      return None
  
  
  def test_type_error_w_positional_arguments():
      def function_00(the_input):
          return None
  
      function_00('a')
      function_01('a', 'b')
  
      def function_02(first, second, third):
  

  the terminal is my friend, and shows TypeError

  TypeError: function_01() got
             multiple values for argument 'first'
  

  because the call to function_01 from test_type_error_w_args_and_kwargs uses 1 as the value for the first argument which is first in the definition, and uses 0 as the value for first as a keyword argument.

• I change the call from test_type_error_w_args_and_kwargs to only use positional arguments to make it clearer

  the test passes because the call to the function matches its definition.

• I add a call to function_02 with arguments that are not clear

  the terminal is my friend, and shows NameError

  NameError: name 'function_02' is not defined
  

  because function_02 belongs to the test_type_error_w_positional_arguments function and I cannot reach it from outside test_type_error_w_positional_arguments.

• I move function_02 out of test_type_error_w_positional_arguments so that it can be called from anywhere in the file

  def function_01(first, second):
      return None
  
  
  def function_02(first, second, third):
      return None
  

  the terminal is my friend, and shows TypeError

  TypeError: function_02() got
             multiple values for argument 'first'
  

  because the call to function_02 from test_type_error_w_args_and_kwargs uses False as the first positional argument which is named first in the definition, and uses None as the value for first as a keyword argument.

• I change the first value in the call from test_type_error_w_args_and_kwargs to a keyword argument to make it clearer

  the terminal is my friend, and shows TypeError

  TypeError: function_02() missing
             1 required positional argument: 'third'
  

  because

  • the call to function_02 from test_type_error_w_args_and_kwargs uses two arguments.

  • the function definition (signature) of function_02 takes three arguments (first, second and third).

• I add a third argument to the call

  the terminal is my friend, and shows TypeError

  TypeError: function_02() got
             multiple values for argument 'first'
  

  because the call to function_02 from test_type_error_w_args_and_kwargs uses True as the first positional argument which is named first in the definition, and uses None as the value for first as a keyword argument.

• I change the call from test_type_error_w_args_and_kwargs to use a keyword argument for True, to make it clearer

  the test passes because the call to the function matches its definition.

• I add a call to function_03

  the terminal is my friend, and shows NameError

  NameError: name 'function_03' is not defined
  

  because function_03 belongs to the test_type_error_w_positional_arguments function and I cannot reach it from outside test_type_error_w_positional_arguments.

• I move function_03 out of test_type_error_w_positional_arguments

  the terminal is my friend, and shows TypeError

  TypeError: function_03() got
             multiple values for argument 'first'
  

  because the call uses an argument in the first position and uses a keyword argument with the same name as the argument in the first position.

• I add a keyword argument for the first value in the call to function_03 from test_type_error_w_args_and_kwargs to make it clearer

  the test passes because the call to the function matches its definition.

• I add a call to function_07 from test_type_error_w_args_and_kwargs

  the terminal is my friend, and shows NameError

  NameError: name 'function_07' is not defined
  

  because function_07 belongs to the test_type_error_w_keyword_arguments function and I cannot reach it from outside test_type_error_w_keyword_arguments.

• I move function_07 out of test_type_error_w_keyword_arguments

  the terminal is my friend, and shows TypeError

  TypeError: function_07() got
             multiple values for argument 'argument_0'
  

  because

  • the call to function_07 from test_type_error_w_args_and_kwargs uses an argument in the first position and uses a keyword argument with the same name as the argument in the first position.

  • the function definition (signature) of function_07 takes four arguments. How does Python know which value to use for argument_0 if I use both the position and the name of the argument for two values?

  • the call to a function must match its signature (definition).

• I change the call to use a keyword argument, then change its position

  the terminal still shows TypeError because the call uses an argument in the first position and uses a keyword argument with the same name as the argument in the first position.

• I use a keyword argument to make it clearer

  the test passes because the call to the function matches its definition.

• I add a call to function_00 from test_type_error_w_args_and_kwargs

  the terminal is my friend, and shows NameError

  NameError: name 'function_00' is not defined
  

  because function_00 belongs to the test_type_error_w_positional_arguments function and I cannot reach it from outside test_type_error_w_positional_arguments.

• I move function_00 out of test_type_error_w_positional_arguments

  def function_00(the_input):
      return None
  
  
  def function_01(first, second):
      return None
  

  the terminal is my friend, and shows TypeError

  TypeError: function_00() got
             multiple values for argument 'the_input'
  

  because

  • the call to function_00 from test_type_error_w_args_and_kwargs uses an argument in the first position and uses a keyword argument with the same name as the argument in the first position.

  • the function definition (signature) of function_00 takes one argument. How does Python know which value to use for the_input if I use both the position and the name of the argument?

  • the call to a function must match its signature (definition).

• I change the call to function_00 from test_type_error_w_args_and_kwargs to match the signature

  the test passes because the call to the function matches its definition.

• I add a call to function_04 from test_type_error_w_args_and_kwargs

  the terminal is my friend, and shows NameError

  NameError: name 'function_04' is not defined
  

  because function_04 belongs to the test_type_error_w_keyword_arguments function and I cannot reach it from outside test_type_error_w_keyword_arguments.

• I move function_04 out of test_type_error_w_keyword_arguments

  the terminal is my friend, and shows TypeError

  TypeError: function_04() got
             multiple values for argument 'argument'
  

  because

  • the call to function_04 from test_type_error_w_args_and_kwargs uses an argument in the first position and uses a keyword argument with the same name as the argument in the first position.

  • the function definition (signature) of function_04 takes one argument. How does Python know which value to use for argument if I use both the position and the name of the argument?

  • the call to a function must match its signature (definition).

• I change the call to function_04 from test_type_error_w_args_and_kwargs to match the signature

  the test passes because the call to the function matches its definition.

• I add a call to function_05 from test_type_error_w_args_and_kwargs

  the terminal is my friend, and shows NameError

  NameError: name 'function_05' is not defined
  

• I move function_05 out of test_type_error_w_keyword_arguments

  the terminal is my friend, and shows TypeError

  TypeError: function_05() got
             multiple values for argument 'argument_0'
  

  because …

• I change the call to function_05 from test_type_error_w_args_and_kwargs to make it match the signature

  the test passes because the call to the function matches its definition.

• I add a call to function_06 from test_type_error_w_args_and_kwargs

  the terminal is my friend, and shows NameError

  NameError: name 'function_06' is not defined
  

  because function_06 belongs to the test_type_error_w_keyword_arguments function.

• I move function_06 out of test_type_error_w_keyword_arguments

  the terminal is my friend, and shows TypeError

  TypeError: function_06() got
             multiple values for argument 'argument_1'
  

• I use another keyword argument in the call to function_06 from test_type_error_w_args_and_kwargs

  the terminal is my friend, and shows TypeError

  TypeError: function_06() got
             multiple values for argument 'argument_0'
  

• I use one more keyword argument to make it clearer

  the test passes because the call to the function matches its definition.

• I remove the commented lines from test_type_error_w_args_and_kwargs

• I add a git commit message in the other terminal

  terminal

  git commit --all --message \
  'add test_type_error_w_args_and_kwargs'
  

---

test TypeError with required and unexpected arguments

---

RED: make it fail

---

• I go back to the terminal where the tests are running

• I add a call to function_03 from test_type_error_w_keyword_arguments

  the terminal is my friend, and shows TypeError

  TypeError: function_03() missing
             1 required positional argument: 'fourth'
  

  because the signature only allows calls with four inputs, and it got called with three.

---

GREEN: make it pass

---

I add fourth with a value to the call

def test_type_error_w_keyword_arguments():
    function_03(
        first=None,
        second=False,
        third=True,
        fourth=4,
    )
    function_04(argument='value')

the test passes because the call to the function matches its definition.

---

REFACTOR: make it better

---

• I add a call to function_02 from test_type_error_w_keyword_arguments

  the terminal is my friend, and shows TypeError

  TypeError: function_02() got
             an unexpected keyword argument 'fourth'
  

  because the call uses a name (fourth) that is not in the parentheses of its definition.

• I remove the unexpected keyword argument from the call

  the test passes because the call to the function matches its definition.

• I add a call to function_01 from test_type_error_w_keyword_arguments

  the terminal is my friend, and shows TypeError

  TypeError: function_01() missing
             1 required positional argument: 'first'
  

  because the signature only allows calls with two inputs, and it got called with one.

• I change the call to match the signature

  the test passes because the call to the function matches its definition.

• I add a call to function_00 from test_type_error_w_keyword_arguments

  the terminal is my friend, and shows TypeError

  TypeError: function_00() got
             an unexpected keyword argument 'second'
  

  because the call uses a name (second) that …

• I remove second from the call from test_type_error_w_keyword_arguments

  the terminal is my friend, and shows TypeError

  TypeError: function_00() got
             an unexpected keyword argument 'first'
  

  because the call …

• I remove first from the call

  the terminal is my friend, and shows TypeError

  TypeError: function_00() missing
             1 required positional argument: 'the_input'
  

• I use the name in the call

  the test passes because I used the same name in the definition of the function when I called it with keyword arguments.

• I move the call to function_08 from test_type_error_w_args_and_kwargs that uses keyword arguments to test_type_error_w_keyword_arguments

  the terminal is my friend, and shows NameError

  NameError: name 'function_08' is not defined
  

• I move function_08 out of test_type_error_w_args_and_kwargs

  the test is green again.

• I remove the commented lines from test_type_error_w_keyword_arguments

---

• I add a call to function_04 from test_type_error_w_positional_arguments

  the terminal is my friend, and shows TypeError

  TypeError: function_04() missing
             1 required positional argument: 'argument'
  

• I add a value to the call to function_04

  the test passes because the call to the function matches its definition.

• I add a call to function_05 from test_type_error_w_positional_arguments

  the terminal is my friend, and shows TypeError

  TypeError: function_05() takes
             2 positional arguments but 3 were given
  

• I remove a value from the call to function_05

  the test passes because the call to the function matches its definition.

• I add a call to function_06 from test_type_error_w_positional_arguments

  the terminal is my friend, and shows TypeError

  TypeError: function_06() missing
             1 required positional argument: 'argument_2'
  

• I add a value to the call to function_06

  the test passes because the call to the function matches its definition.

• I add a call to function_07 from test_type_error_w_positional_arguments

  the terminal is my friend, and shows TypeError

  TypeError: function_07() takes
             4 positional arguments but 5 were given
  

• I remove a value from the call to function_07

  the test passes because the call to the function matches its definition.

• I add a call to function_08 from test_type_error_w_positional_arguments

  the terminal is my friend, and shows TypeError

  TypeError: function_08() missing
             1 required positional argument: 'argument'
  

• I add a value to the call to function_08

  the test passes because the call to the function matches its definition.

• I remove the commented lines from test_type_error_w_positional_arguments

• I add a git commit message in the other terminal

  git commit --all --message \
  'test with required and unexpected arguments'
  

I have to call a function with the same number or names of arguments that are in its definition.

---

close the project

• I close test_type_error.py

• I click in the terminal where the tests are running

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

• I change directory to the parent of type_error

  terminal

  cd ..
  

  the terminal shows

  .../pumping_python
  

  I am back in the pumping_python directory.

---

review

I ran tests for TypeError with

• positional arguments

• keyword arguments

• positional and keyword arguments

My problem with the tests is that they all show the correct way to call the functions I made in the file. If someone reads the file or runs it, there is no way for them to know how any of the calls are related to TypeError unless they go through the process with me, there has to be a better way.

---

code from the chapter

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

---

what is next?

• I know how to make a Python Test Driven Development environment manually.

• I know what a Python module is.

• I know how to run tests automatically.

• I know what an assertion is.

• I know how to make functions.

• I know how to make a person with strings.

• I know how to make functions that take input.

• I know what causes TypeError.

Would you like to test AssertionError with functions that take input?

---

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