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"""关键字参数
@see: https://docs.python.org/3/tutorial/controlflow.html#keyword-arguments
函数可以使用 kwarg=value 形式的关键字参数来调用。
"""
import pytest
def parrot(voltage, state='a stiff', action='voom', parrot_type='Norwegian Blue'):
"""多参数函数的示例
这个函数接受一个必选参数(voltage)和三个可选参数
(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():
"""测试使用指定关键字参数的调用函数"""
# parrot函数接受一个必选参数 (voltage) 还有三个可选参数 (state, action, type).
# 这个函数可以通过以下任何一种方式被调用:
message = (
"This parrot wouldn't voom if you put 1000 volts through it. "
"Lovely plumage, the Norwegian Blue. "
"It's a stiff!"
)
# 1 位置参数
assert parrot(1000) == message
# 1 关键字参数
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 关键字参数
assert parrot(voltage=1000000, action='VOOOOOM') == message
# 2 关键字参数
assert parrot(action='VOOOOOM', voltage=1000000) == message
# 3 位置参数
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 位置, 1 关键字
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
# 但是下面所有的调用都是无效的。
with pytest.raises(Exception):
# 必须参数缺失.
# pylint: disable=no-value-for-parameter
parrot()
# 在关键字参数之后的非关键字参数。
# parrot(voltage=5.0, 'dead')
with pytest.raises(Exception):
# pylint: disable=redundant-keyword-arg
parrot(110, voltage=220)
with pytest.raises(Exception):
# 未知的关键字参数
# pylint: disable=unexpected-keyword-arg,no-value-for-parameter
parrot(actor='John Cleese')
# 在函数调用中，关键字参数必须跟在位置参数之后。传递的所有关键字参数必须与函数接受的其中一个参数匹配 (例如actor不是parrot函数的有效参数),
# 它们的顺序并不重要。这也包括非可选参数(例如parrot(voltage=1000)也是有效的)。 参数不能接收一个值超过一次。
# 下面是一个由于这种限制而失败的示例:
def function_with_one_argument(number):
return number
with pytest.raises(Exception):
# pylint: disable=redundant-keyword-arg
function_with_one_argument(0, number=0)
# 当出现 **name 的最后一个正式形参时，它将接收一个字典，其中包含除与正式形参对应的关键字参数外的所有关键字参数。
# 这可以与 *name 的形式参数结合使用，该形式参数接收一个包含形式参数列表之外的位置参数的元组。
# (*name 必须出现在 **name 之前。)
# 例如，如果我们这样定义一个函数:
def test_function(first_param, *arguments, **keywords):
"""这个函数通过“arguments”元组和关键字字典接受它的参数。"""
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',
)