桂桂卷的入职准备-python学习

Posted by CYY on March 30, 2022

💗入职前的草莓桂桂卷(๑•̀ㅂ•́)و✧

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4.8.1-Default Argument Values

🍓Example 1

Important warning: The default value is evaluated only once. This makes a difference when the default is a mutable object such as a list, dictionary, or instances of most classes. For example, the following function accumulates the arguments passed to it on subsequent calls:

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def f(a, L=[]):
    L.append(a)
    return L

print(f(1))
print(f(2)) 
print(f(3))

输出

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3
[1]
[1, 2]
[1, 2, 3]

If you don’t want the default to be shared between subsequent calls, you can write the function like this instead:

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def f(a, L=None):
    if L is None:
        L = []
    L.append(a)
    return L

这里