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"""Keyword Arguments
@see: https://docs.python.org/3/tutorial/controlflow.html#keyword-arguments
Functions can be called using keyword arguments of the form kwarg=value.
"""
import pytest
def parrot(voltage, state='a stiff', action='voom', parrot_type='Norwegian Blue'):
"""Example of multi-argument function
This function accepts one required argument (voltage) and three optional arguments
(state, action, and type).
"""
message = 'This parrot wouldn\'t ' + action + ' '
message += 'if you put ' + str(voltage) + ' volts through it. '
message += 'Lovely plumage, the ' + parrot_type + '. '
message += 'It\'s ' + state + '!'
return message
def test_function_keyword_arguments():
"""Test calling function with specifying keyword arguments"""
# The parrot function accepts one required argument (voltage) and three optional arguments
# (state, action, and type). This function can be called in any of the following ways:
message = (
"This parrot wouldn't voom if you put 1000 volts through it. "
"Lovely plumage, the Norwegian Blue. "
"It's a stiff!"
)
# 1 positional argument
assert parrot(1000) == message
# 1 keyword argument
assert parrot(voltage=1000) == message
message = (
"This parrot wouldn't VOOOOOM if you put 1000000 volts through it. "
"Lovely plumage, the Norwegian Blue. "
"It's a stiff!"
)
# 2 keyword arguments
assert parrot(voltage=1000000, action='VOOOOOM') == message
# 2 keyword arguments
assert parrot(action='VOOOOOM', voltage=1000000) == message
# 3 positional arguments
message = (
"This parrot wouldn't jump if you put 1000000 volts through it. "
"Lovely plumage, the Norwegian Blue. "
"It's bereft of life!"
)
assert parrot(1000000, 'bereft of life', 'jump') == message
# 1 positional, 1 keyword
message = (
"This parrot wouldn't voom if you put 1000 volts through it. "
"Lovely plumage, the Norwegian Blue. "
"It's pushing up the daisies!"
)
assert parrot(1000, state='pushing up the daisies') == message
# But all the following calls would be invalid.
with pytest.raises(Exception):
# Required argument missing.
# pylint: disable=no-value-for-parameter
parrot()
# Non-keyword argument after a keyword argument.
# parrot(voltage=5.0, 'dead')
with pytest.raises(Exception):
# pylint: disable=redundant-keyword-arg
parrot(110, voltage=220)
with pytest.raises(Exception):
# unknown keyword argument
# pylint: disable=unexpected-keyword-arg,no-value-for-parameter
parrot(actor='John Cleese')
# In a function call, keyword arguments must follow positional arguments. All the keyword
# arguments passed must match one of the arguments accepted by the function (e.g. actor is not
# a valid argument for the parrot function), and their order is not important. This also
# includes non-optional arguments (e.g. parrot(voltage=1000) is valid too). No argument may
# receive a value more than once. Here’s an example that fails due to this restriction:
def function_with_one_argument(number):
return number
with pytest.raises(Exception):
# pylint: disable=redundant-keyword-arg
function_with_one_argument(0, number=0)
# When a final formal parameter of the form **name is present, it receives a dictionary
# containing all keyword arguments except for those corresponding to a formal parameter.
# This may be combined with a formal parameter of the form *name which receives a tuple
# containing the positional arguments beyond the formal parameter list.
# (*name must occur before **name.) For example, if we define a function like this:
def test_function(first_param, *arguments, **keywords):
"""This function accepts its arguments through "arguments" tuple and keywords dictionary."""
assert first_param == 'first param'
assert arguments == ('second param', 'third param')
assert keywords == {
'fourth_param_name': 'fourth named param',
'fifth_param_name': 'fifth named param'
}
test_function(
'first param',
'second param',
'third param',
fourth_param_name='fourth named param',
fifth_param_name='fifth named param',
)