Python3基础 函数 参数为list 使用+=会影响到外部的实参

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• ???????Python : 3.7.3
• ?????????OS : Ubuntu 18.04.2 LTS
• ????????IDE : pycharm-community-2019.1.3
• ??????Conda : 4.7.5
• ???typesetting : Markdown

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code

"""
@Author : 行初心
@Date   : 2019/7/4
@Blog   : www.cnblogs.com/xingchuxin
@Gitee  : gitee.com/zhichengjiu
"""

def change(num_list: list):
    # 列表使用+=，本质上是调用extend方法！
    # 不修改引用，整合列表，改变外部实参
    # 此等细节...
    num_list += [1]
    print("def +=", id(num_list))

    # 使用 +...=
    # 这样写，没有调用方法。修改了引用，外部实参不受影响。
    num_list = num_list + [1, 2, 3]
    print("def +...=", id(num_list))

def main():
    num_list = [0, 1, 2, 3]
    print("main", id(num_list))
    print("main", num_list)
    change(num_list)
    print("main change", id(num_list))
    print("main change", num_list)
    # 多使用id函数，自然解开疑惑

if __name__ == '__main__':
    main()

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result

/home/coder/anaconda3/envs/py37/bin/python /home/coder/PycharmProjects/Base/demo.py
main 140265422970760
main [0, 1, 2, 3]
def += 140265422970760
def +...= 140265422204360
main change 140265422970760
main change [0, 1, 2, 3, 1]

Process finished with exit code 0

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source_code

def extend(self, *args, **kwargs): # real signature unknown
    """ Extend list by appending elements from the iterable. """
    pass

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resource

• [文档 - English] docs.python.org/3
• [文档 - 中文] docs.python.org/zh-cn/3
• [规范] www.python.org/dev/peps/pep-0008
• [规范] zh-google-styleguide.readthedocs.io/en/latest/google-python-styleguide/python_language_rules
• [源码] www.python.org/downloads/source
• [ PEP ] www.python.org/dev/peps
• [平台] www.cnblogs.com
• [平台] gitee.com

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原文地址：https://www.cnblogs.com/xingchuxin/p/11135312.html