python的可变长度参数(*args)是否在函数调用时扩展生成器?
问题描述
考虑以下 Python 代码:
Consider the following Python code:
def f(*args):
for a in args:
pass
foo = ['foo', 'bar', 'baz']
# Python generator expressions FTW
gen = (f for f in foo)
f(*gen)
*args 会在调用时自动扩展生成器吗?换句话说，我是否在 f(*gen) 内对 gen 进行了两次迭代，一次是展开 *args，一次是对 args 进行迭代?还是生成器保持原始状态，而迭代只在 for 循环中发生一次?
Does *args automatically expand the generator at call-time? Put another way, am I iterating over gen twice within f(*gen), once to expand *args and once to iterate over args? Or is the generator preserved in pristine condition, while iteration only happens once during the for loop?
解决方案
生成器在函数调用时展开，您可以轻松查看:
The generator is expanded at the time of the function call, as you can easily check:
def f(*args):
print(args)
foo = ['foo', 'bar', 'baz']
gen = (f for f in foo)
f(*gen)
将打印
('foo', 'bar', 'baz')
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