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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‘, ‘醜‘: ‘牛‘, ‘寅‘: ‘虎‘,
               ‘卯‘: ‘兔‘, ‘辰‘: ‘龍‘, ‘巳‘: ‘蛇‘,
               ‘午‘: ‘馬‘, ‘未‘: ‘羊‘, ‘申‘: ‘猴‘,
               ‘酉‘: ‘雞‘, ‘戌‘: ‘狗‘, ‘亥‘: ‘豬‘}

    # 如果找不到，就會添加.
    # 顯然鍵 ‘子‘存在，那麽 值 ‘屬鼠‘ 也就無用
    print(my_dict.setdefault(‘子‘, ‘屬鼠‘))

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

    # 如果找不到，就會添加.
    print(my_dict.setdefault(‘行初心‘, ‘博客園‘))
    print(my_dict)

    # 不存在的鍵"行"，未指定值，默認返回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
博客園
{‘子‘: ‘鼠‘, ‘醜‘: ‘牛‘, ‘寅‘: ‘虎‘, ‘卯‘: ‘兔‘, ‘辰‘: ‘龍‘, ‘巳‘: ‘蛇‘, ‘午‘: ‘馬‘, ‘未‘: ‘羊‘, ‘申‘: ‘猴‘, ‘酉‘: ‘雞‘, ‘戌‘: ‘狗‘, ‘亥‘: ‘豬‘, ‘行初心‘: ‘博客園‘}
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

• [文檔] https://docs.python.org/3/
• [規範] https://www.python.org/dev/peps/pep-0008/
• [規範] https://zh-google-styleguide.readthedocs.io/en/latest/google-python-styleguide/python_language_rules/
• [源碼] https://www.python.org/downloads/source/
• [ PEP ] https://www.python.org/dev/peps/
• [平臺] https://www.cnblogs.com/

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Python具有開源、跨平臺、解釋型、交互式等特性，值得學習。
Python的設計哲學：優雅，明確，簡單。提倡用一種方法，最好是只有一種方法來做一件事。
代碼的書寫要遵守規範，這樣有助於溝通和理解。
每種語言都有獨特的思想，初學者需要轉變思維、踏實踐行、堅持積累。

Python3基礎 dict setdefault 根據鍵查找值，找不到鍵會添加