Python中的**kwargs有什么用途?
我知道你可以在表上执行objects.filter并传递一个**kwargs参数。
我也可以这样做来指定时间增量,即时间增量(小时=时间1)吗?
它到底是如何工作的?是否归类为“开箱”?比如a,b=1,2?
Python中的**kwargs有什么用途?
我知道你可以在表上执行objects.filter并传递一个**kwargs参数。
我也可以这样做来指定时间增量,即时间增量(小时=时间1)吗?
它到底是如何工作的?是否归类为“开箱”?比如a,b=1,2?
当前回答
下面是一个我希望有帮助的例子:
#! /usr/bin/env python
#
def g( **kwargs) :
print ( "In g ready to print kwargs" )
print kwargs
print ( "in g, calling f")
f ( **kwargs )
print ( "In g, after returning from f")
def f( **kwargs ) :
print ( "in f, printing kwargs")
print ( kwargs )
print ( "In f, after printing kwargs")
g( a="red", b=5, c="Nassau")
g( q="purple", w="W", c="Charlie", d=[4, 3, 6] )
运行程序时,您将获得:
$ python kwargs_demo.py
In g ready to print kwargs
{'a': 'red', 'c': 'Nassau', 'b': 5}
in g, calling f
in f, printing kwargs
{'a': 'red', 'c': 'Nassau', 'b': 5}
In f, after printing kwargs
In g, after returning from f
In g ready to print kwargs
{'q': 'purple', 'c': 'Charlie', 'd': [4, 3, 6], 'w': 'W'}
in g, calling f
in f, printing kwargs
{'q': 'purple', 'c': 'Charlie', 'd': [4, 3, 6], 'w': 'W'}
In f, after printing kwargs
In g, after returning from f
这里的关键是调用中命名参数的可变数量转换为函数中的字典。
其他回答
这是了解python解包的简单示例,
>>> def f(*args, **kwargs):
... print 'args', args, 'kwargs', kwargs
eg1:
>>>f(1, 2)
>>> args (1,2) kwargs {} #args return parameter without reference as a tuple
>>>f(a = 1, b = 2)
>>> args () kwargs {'a': 1, 'b': 2} #args is empty tuple and kwargs return parameter with reference as a dictionary
基于一个好的示例有时比一个长的论述更好,我将使用所有python变量参数传递工具(位置和命名参数)编写两个函数。你应该能够很容易地自己看到它的作用:
def f(a = 0, *args, **kwargs):
print("Received by f(a, *args, **kwargs)")
print("=> f(a=%s, args=%s, kwargs=%s" % (a, args, kwargs))
print("Calling g(10, 11, 12, *args, d = 13, e = 14, **kwargs)")
g(10, 11, 12, *args, d = 13, e = 14, **kwargs)
def g(f, g = 0, *args, **kwargs):
print("Received by g(f, g = 0, *args, **kwargs)")
print("=> g(f=%s, g=%s, args=%s, kwargs=%s)" % (f, g, args, kwargs))
print("Calling f(1, 2, 3, 4, b = 5, c = 6)")
f(1, 2, 3, 4, b = 5, c = 6)
下面是输出:
Calling f(1, 2, 3, 4, b = 5, c = 6)
Received by f(a, *args, **kwargs)
=> f(a=1, args=(2, 3, 4), kwargs={'c': 6, 'b': 5}
Calling g(10, 11, 12, *args, d = 13, e = 14, **kwargs)
Received by g(f, g = 0, *args, **kwargs)
=> g(f=10, g=11, args=(12, 2, 3, 4), kwargs={'c': 6, 'b': 5, 'e': 14, 'd': 13})
此外,您还可以在调用kwargs函数时混合使用不同的用法:
def test(**kwargs):
print kwargs['a']
print kwargs['b']
print kwargs['c']
args = { 'b': 2, 'c': 3}
test( a=1, **args )
给出以下输出:
1
2
3
注意,**kwargs必须是最后一个参数
kwargs是一种语法糖,可以将名称参数作为字典传递(对于func),或将字典作为命名参数传递(对于func)
下面是一个我希望有帮助的例子:
#! /usr/bin/env python
#
def g( **kwargs) :
print ( "In g ready to print kwargs" )
print kwargs
print ( "in g, calling f")
f ( **kwargs )
print ( "In g, after returning from f")
def f( **kwargs ) :
print ( "in f, printing kwargs")
print ( kwargs )
print ( "In f, after printing kwargs")
g( a="red", b=5, c="Nassau")
g( q="purple", w="W", c="Charlie", d=[4, 3, 6] )
运行程序时,您将获得:
$ python kwargs_demo.py
In g ready to print kwargs
{'a': 'red', 'c': 'Nassau', 'b': 5}
in g, calling f
in f, printing kwargs
{'a': 'red', 'c': 'Nassau', 'b': 5}
In f, after printing kwargs
In g, after returning from f
In g ready to print kwargs
{'q': 'purple', 'c': 'Charlie', 'd': [4, 3, 6], 'w': 'W'}
in g, calling f
in f, printing kwargs
{'q': 'purple', 'c': 'Charlie', 'd': [4, 3, 6], 'w': 'W'}
In f, after printing kwargs
In g, after returning from f
这里的关键是调用中命名参数的可变数量转换为函数中的字典。