关键字参数
kwarg=value
形式的 关键字参数 也可以用于调用函数。函数示例如下:
def parrot(voltage, state='a stiff', action='voom', type='Norwegian Blue'):
print("-- This parrot wouldn't", action, end=' ')
print("if you put", voltage, "volts through it.")
print("-- Lovely plumage, the", type)
print("-- It's", state, "!")
该函数接受一个必选参数(voltage
)和三个可选参数(state
, action
和 type
)。该函数可用下列方式调用:
parrot(1000) # 1 positional argument
parrot(voltage=1000) # 1 keyword argument
parrot(voltage=1000000, action='VOOOOOM') # 2 keyword arguments
parrot(action='VOOOOOM', voltage=1000000) # 2 keyword arguments
parrot('a million', 'bereft of life', 'jump') # 3 positional arguments
parrot('a thousand', state='pushing up the daisies') # 1 positional, 1 keyword
以下调用函数的方式都无效:
parrot() # required argument missing
parrot(voltage=5.0, 'dead') # non-keyword argument after a keyword argument
parrot(110, voltage=220) # duplicate value for the same argument
parrot(actor='John Cleese') # unknown keyword argument
函数调用时,关键字参数必须跟在位置参数后面。所有传递的关键字参数都必须匹配一个函数接受的参数(比如,actor
不是函数 parrot
的有效参数),关键字参数的顺序并不重要。这也包括必选参数,(比如,parrot(voltage=1000)
也有效)。不能对同一个参数多次赋值,下面就是一个因此限制而失败的例子:
>>> def function(a):
... pass
...
>>> function(0, a=0)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: function() got multiple values for argument 'a'
最后一个形参为 **name
形式时,接收一个字典(详见 映射类型 --- dict),该字典包含与函数中已定义形参对应之外的所有关键字参数。**name
形参可以与 *name
形参(下一小节介绍)组合使用(*name
必须在 **name
前面), *name
形参接收一个 元组,该元组包含形参列表之外的位置参数。例如,可以定义下面这样的函数:
def cheeseshop(kind, *arguments, **keywords):
print("-- Do you have any", kind, "?")
print("-- I'm sorry, we're all out of", kind)
for arg in arguments:
print(arg)
print("-" * 40)
for kw in keywords:
print(kw, ":", keywords[kw])
该函数可以用如下方式调用:
cheeseshop("Limburger", "It's very runny, sir.",
"It's really very, VERY runny, sir.",
shopkeeper="Michael Palin",
client="John Cleese",
sketch="Cheese Shop Sketch")
输出结果如下:
-- Do you have any Limburger ?
-- I'm sorry, we're all out of Limburger
It's very runny, sir.
It's really very, VERY runny, sir.
----------------------------------------
shopkeeper : Michael Palin
client : John Cleese
sketch : Cheese Shop Sketch
注意,关键字参数在输出结果中的顺序与调用函数时的顺序一致。
标签:yyds,keyword,parrot,python,argument,干货,参数,voltage,print From: https://blog.51cto.com/u_12891160/6482724