*tuple 和 **dict 在 Python 中是什么意思？
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/21809112/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
What does *tuple and **dict means in Python?
提问by heLomaN
As mentioned in PythonCookbook, *can be added before a tuple, and what does *mean here?
正如PythonCookbook中提到的，*可以在元组之前添加，*这里是什么意思？
Chapter 1.18. Mapping Names to Sequence Elements:
第 1.18 章。将名称映射到序列元素：
from collections import namedtuple
Stock = namedtuple('Stock', ['name', 'shares', 'price'])
s = Stock(*rec)
# here rec is an ordinary tuple, for example: rec = ('ACME', 100, 123.45)
In the same section, **dictpresents:
在同一部分，**dict介绍：
from collections import namedtuple
Stock = namedtuple('Stock', ['name', 'shares', 'price', 'date', 'time'])
# Create a prototype instance
stock_prototype = Stock('', 0, 0.0, None, None)
# Function to convert a dictionary to a Stock
def dict_to_stock(s):
return stock_prototype._replace(**s)
What is **'s function here?
**这里的功能是什么？
采纳答案by Elazar
In a function call
在函数调用中
*tmeans "treat the elements of this tuple as positional arguments to this function call."
*t表示“将此元组的元素视为此函数调用的位置参数。”
def foo(x, y):
print(x, y)
>>> t = (1, 2)
>>> foo(*t)
1 2
Since v3.5, you can also do this in a list/tuple/set literals:
从 v3.5 开始，您还可以在列表/元组/集文字中执行此操作：
>>> [1, *(2, 3), 4]
[1, 2, 3, 4]
**dmeans "treat the key-value pairs in the dictionary as additional named arguments to this function call."
**d表示“将字典中的键值对视为此函数调用的附加命名参数。”
def foo(x, y):
print(x, y)
>>> d = {'x':1, 'y':2}
>>> foo(**d)
1 2
Since v3.5, you can also do this in a dictionary literals:
从 v3.5 开始，您还可以在字典文字中执行此操作：
>>> d = {'a': 1}
>>> {'b': 2, **d}
{'b': 2, 'a': 1}
In a function signature
在函数签名中
*tmeans "take all additional positional arguments to this function and pack them into this parameter as a tuple."
*t意思是“将所有额外的位置参数带到这个函数中，并将它们作为一个元组打包到这个参数中。”
def foo(*t):
print(t)
>>> foo(1, 2)
(1, 2)
**dmeans "take all additional named arguments to this function and insert them into this parameter as dictionary entries."
**d意思是“将所有额外的命名参数带到这个函数中，并将它们作为字典条目插入到这个参数中。”
def foo(**d):
print(d)
>>> foo(x=1, y=2)
{'y': 2, 'x': 1}
In assignments and forloops
在作业和for循环中
*xmeans "consume additional elements in the right hand side", but it doesn't have to be the last item. Note that xwill always be a list:
*x表示“在右侧消耗其他元素”，但它不必是最后一项。请注意，这x将始终是一个列表：
>>> x, *xs = (1, 2, 3, 4)
>>> x
1
>>> xs
[2, 3, 4]
>>> *xs, x = (1, 2, 3, 4)
>>> xs
[1, 2, 3]
>>> x
4
>>> x, *xs, y = (1, 2, 3, 4)
>>> x
1
>>> xs
[2, 3]
>>> y
4
>>> for (x, *y, z) in [ (1, 2, 3, 4) ]: print(x, y, z)
...
1 [2, 3] 4
Note that parameters that appear after a *are keyword-only:
请注意，出现在 a 之后的*参数仅是关键字：
def f(a, *, b): ...
f(1, b=2) # fine
f(1, 2) # error: b is keyword-only
Python3.8 added positional-only parameters, meaning parameters that cannot be used as keyword arguments. They are appear before a /(a pun on *for keyword args).
Python3.8 添加了positional-only parameters，表示不能用作关键字参数的参数。它们出现在 a 之前/（*关键字 args的双关语）。
def f(a, /, p, *, k): ...
f( 1, 2, k=3) # fine
f( 1, p=2, k=3) # fine
f(a=1, p=2, k=3) # error: a is positional-only
