问题
Please see the code below:-
#!/usr/bin/python
# Filename: total.py
def total(initial=5, *numbers, **keywords):
count = initial
for number in numbers:
count += number
for key in keywords:
count += keywords[key]
return count
print(total(10, 1, 2, 3, vegetables=50, fruits=100))
Can someone please explain how is *numbers and **keywords picking up the arguments? A simple explaination is very much appreciayed Thanks in advance
回答1:
In your code numbers is assigned the (1,2,3) tuple. keywords is assigned a dictionary, containing vegetables and fruits.
One star (*) defines positional arguments. This means that you can receive any number of arguments. You can treat the passed arguments as a tuple.
Two stars (**) define keywords arguments.
The reference material is available here.
Examples
Python 2.x (before keyword-only arguments)
def foo(x, y, foo=None, *args): print [x, y, foo, args]
foo(1, 2, 3, 4) --> [1, 2, 3, (4, )] # foo == 4
foo(1, 2, 3, 4, foo=True) --> TypeError
Python 3.x (with keyword-only arguments)
def foo(x, y, *args, foo=None): print([x, y, foo, args])
foo(1, 2, 3, 4) --> [1, 2, None, (3, 4)] # foo is None
foo(1, 2, 3, 4, foo=True) --> [1, 2, True, (3, 4)]
def combo(x=None, *args, y=None): ... # 2.x and 3.x styles in one function
Although a seasoned programmer understands what happened in 2.x, it's counter-intuitive (a positional argument gets bound to foo= regardless of keyword arguments as long as there are enough positional arguments)
Python 3.x introduces more intuitive keyword-only arguments with PEP-3102 (keyword arguments after varargs can only be bound by name)
来源：https://stackoverflow.com/questions/4255091/explain-keyword-only-arguments-varargs-in-python