Python3基础 dict setdefault 根据键查找值，找不到键会添加

Posted 2021-01-08 xingchuxin

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•                    python : 3.7.0
•                           OS : Ubuntu 18.04.1 LTS
  
•                          IDE : PyCharm 2018.2.4
•                      conda : 4.5.11
•            type setting : Markdown

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code

"""
@Author : 行初心
@Date   : 18-9-23
@Blog   : www.cnblogs.com/xingchuxin
@GitHub : github.com/GratefulHeartCoder
"""


def main():
    my_dict = {‘子‘: ‘鼠‘, ‘丑‘: ‘牛‘, ‘寅‘: ‘虎‘,
               ‘卯‘: ‘兔‘, ‘辰‘: ‘龙‘, ‘巳‘: ‘蛇‘,
               ‘午‘: ‘马‘, ‘未‘: ‘羊‘, ‘申‘: ‘猴‘,
               ‘酉‘: ‘鸡‘, ‘戌‘: ‘狗‘, ‘亥‘: ‘猪‘}

    # 如果找不到，就会添加.
    # 显然键 ‘子‘存在，那么 值 ‘属鼠‘ 也就无用
    print(my_dict.setdefault(‘子‘, ‘属鼠‘))

    # 找得到返回
    print(my_dict.setdefault(‘子‘))

    # 如果找不到，就会添加.
    print(my_dict.setdefault(‘行初心‘, ‘博客园‘))
    print(my_dict)

    # 不存在的键"行"，未指定值，默认返回None
    print(my_dict.setdefault(‘行‘))


if __name__ == ‘__main__‘:
    main()

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result

/home/coder/anaconda3/envs/py37/bin/python /home/coder/PycharmProjects/DataStructure/demo.py
鼠
鼠
博客园
{‘子‘: ‘鼠‘, ‘丑‘: ‘牛‘, ‘寅‘: ‘虎‘, ‘卯‘: ‘兔‘, ‘辰‘: ‘龙‘, ‘巳‘: ‘蛇‘, ‘午‘: ‘马‘, ‘未‘: ‘羊‘, ‘申‘: ‘猴‘, ‘酉‘: ‘鸡‘, ‘戌‘: ‘狗‘, ‘亥‘: ‘猪‘, ‘行初心‘: ‘博客园‘}
None

Process finished with exit code 0

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more knowledge

def setdefault(self, k, d=None): # real signature unknown; restored from __doc__
    """ D.setdefault(k[,d]) -> D.get(k,d), also set D[k]=d if k not in D """
    pass

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resource

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

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