{"id":951897,"date":"2024-12-27T01:14:22","date_gmt":"2024-12-26T17:14:22","guid":{"rendered":"https:\/\/docs.pingcode.com\/ask\/ask-ask\/951897.html"},"modified":"2024-12-27T01:14:25","modified_gmt":"2024-12-26T17:14:25","slug":"python-%e5%a6%82%e4%bd%95%e8%a1%a8%e7%a4%banull","status":"publish","type":"post","link":"https:\/\/docs.pingcode.com\/ask\/951897.html","title":{"rendered":"python \u5982\u4f55\u8868\u793anull"},"content":{"rendered":"

\"python<\/p>\n

\u5728Python\u4e2d\uff0c\u8868\u793anull\u7684\u65b9\u5f0f\u662f\u4f7f\u7528None<\/code>\u5173\u952e\u5b57\u3001None<\/code>\u7528\u4e8e\u8868\u793a\u53d8\u91cf\u6ca1\u6709\u503c\u6216\u7a7a\u503c\u3001\u5728\u51fd\u6570\u6ca1\u6709\u8fd4\u56de\u503c\u65f6\u9ed8\u8ba4\u8fd4\u56deNone<\/code>\u3002<\/strong>Python\u4e2d\u7684None<\/code>\u662f\u4e00\u4e2a\u5bf9\u8c61\uff0c\u8868\u793a\u201c\u4ec0\u4e48\u90fd\u6ca1\u6709\u201d\u7684\u6982\u5ff5\u3002\u5b83\u901a\u5e38\u7528\u4e8e\u521d\u59cb\u5316\u53d8\u91cf\u3001\u5904\u7406\u53ef\u9009\u53c2\u6570\u3001\u8868\u793a\u7f3a\u5931\u6570\u636e\u7b49\u3002\u5728\u4ee5\u4e0b\u5185\u5bb9\u4e2d\uff0c\u6211\u4eec\u5c06\u8be6\u7ec6\u63a2\u8ba8Python\u4e2dNone<\/code>\u7684\u4f7f\u7528\u573a\u666f\u548c\u6ce8\u610f\u4e8b\u9879\u3002<\/p>\n<\/p>\n

\u4e00\u3001NONE<\/code>\u7684\u5b9a\u4e49\u4e0e\u57fa\u672c\u7528\u6cd5<\/p>\n<\/p>\n

\u5728Python\u4e2d\uff0cNone<\/code>\u662f\u4e00\u4e2a\u7279\u6b8a\u7684\u5e38\u91cf\uff0c\u7528\u4e8e\u8868\u793a\u7a7a\u503c\u6216\u6ca1\u6709\u503c\u7684\u60c5\u51b5\u3002\u5b83\u7c7b\u4f3c\u4e8e\u5176\u4ed6\u7f16\u7a0b\u8bed\u8a00\u4e2d\u7684null<\/code>\uff0c\u4f46\u6709\u5176\u72ec\u7279\u7684\u7279\u6027\u3002None<\/code>\u662f\u4e00\u4e2a\u5355\u4f8b\u5bf9\u8c61\uff0c\u8fd9\u610f\u5473\u7740\u5728\u4e00\u4e2aPython\u7a0b\u5e8f\u4e2d\uff0c\u6240\u6709\u7684None<\/code>\u5bf9\u8c61\u90fd\u6307\u5411\u76f8\u540c\u7684\u5185\u5b58\u5730\u5740\u3002<\/p>\n<\/p>\n

    \n
  1. \n

    \u8d4b\u503c\u4e0e\u6bd4\u8f83<\/strong><\/p>\n<\/p>\n

    \u5728Python\u4e2d\uff0c\u60a8\u53ef\u4ee5\u5c06None<\/code>\u8d4b\u503c\u7ed9\u4efb\u4f55\u53d8\u91cf\uff0c\u8868\u793a\u8be5\u53d8\u91cf\u5f53\u524d\u6ca1\u6709\u503c\u3002\u4f8b\u5982\uff1a<\/p>\n<\/p>\n

    x = None<\/p>\n
    <\/code><\/pre>\n<\/p>\n
    \u60a8\u53ef\u4ee5\u4f7f\u7528is<\/code>\u8fd0\u7b97\u7b26\u6765\u68c0\u67e5\u4e00\u4e2a\u53d8\u91cf\u662f\u5426\u4e3aNone<\/code>\uff1a<\/p>\n<\/p>\n
    if x is None:<\/p>\n
        print("x is None")<\/p>\n
    <\/code><\/pre>\n<\/p>\n
    \u8fd9\u91cc\u4f7f\u7528is<\/code>\u800c\u4e0d\u662f==<\/code>\u662f\u56e0\u4e3ais<\/code>\u68c0\u67e5\u7684\u662f\u5bf9\u8c61\u7684\u8eab\u4efd\uff0c\u800c\u4e0d\u662f\u503c\u7684\u76f8\u7b49\u6027\u3002<\/p>\n<\/p>\n<\/li>\n
  2. \n
    \u5728\u51fd\u6570\u4e2d\u7684\u4f7f\u7528<\/strong><\/p>\n<\/p>\n
    \u5f53\u4e00\u4e2a\u51fd\u6570\u6ca1\u6709\u663e\u5f0f\u8fd4\u56de\u503c\u65f6\uff0cPython\u9ed8\u8ba4\u8fd4\u56deNone<\/code>\u3002\u4f8b\u5982\uff1a<\/p>\n<\/p>\n
    def foo():<\/p>\n
        pass<\/p>\n
    result = foo()<\/p>\n
    print(result)  # \u8f93\u51fa: None<\/p>\n
    <\/code><\/pre>\n<\/p>\n<\/li>\n<\/ol>\n
    \u4e8c\u3001NONE<\/code>\u5728\u6570\u636e\u7ed3\u6784\u4e2d\u7684\u5e94\u7528<\/p>\n<\/p>\n
    \u5728\u590d\u6742\u7684\u6570\u636e\u7ed3\u6784\u4e2d\uff0cNone<\/code>\u5e38\u7528\u4e8e\u8868\u793a\u7f3a\u5931\u6216\u672a\u5b9a\u4e49\u7684\u503c\u3002<\/p>\n<\/p>\n
      \n
    1. \n
      \u5217\u8868\u548c\u5b57\u5178\u4e2d\u7684None<\/code><\/strong><\/p>\n<\/p>\n
      \u5728\u5217\u8868\u4e2d\uff0cNone<\/code>\u53ef\u4ee5\u4f5c\u4e3a\u5360\u4f4d\u7b26\uff0c\u8868\u793a\u67d0\u4e9b\u5143\u7d20\u5f53\u524d\u6ca1\u6709\u5b9a\u4e49\uff1a<\/p>\n<\/p>\n
      lst = [1, 2, None, 4]<\/p>\n
      <\/code><\/pre>\n<\/p>\n
      \u5728\u5b57\u5178\u4e2d\uff0cNone<\/code>\u53ef\u4ee5\u7528\u4f5c\u503c\uff0c\u8868\u793a\u67d0\u4e2a\u952e\u6ca1\u6709\u5bf9\u5e94\u7684\u5177\u4f53\u503c\uff1a<\/p>\n<\/p>\n
      dct = {'key1': 'value1', 'key2': None}<\/p>\n
      <\/code><\/pre>\n<\/p>\n<\/li>\n
    2. \n
      \u5904\u7406\u53ef\u9009\u53c2\u6570<\/strong><\/p>\n<\/p>\n
      \u5728\u51fd\u6570\u5b9a\u4e49\u4e2d\uff0cNone<\/code>\u5e38\u7528\u4e8e\u53ef\u9009\u53c2\u6570\u7684\u9ed8\u8ba4\u503c\uff0c\u4fbf\u4e8e\u5728\u51fd\u6570\u4f53\u4e2d\u5224\u65ad\u53c2\u6570\u662f\u5426\u88ab\u63d0\u4f9b\uff1a<\/p>\n<\/p>\n
      def greet(name=None):<\/p>\n
          if name is None:<\/p>\n
              print("Hello, World!")<\/p>\n
          else:<\/p>\n
              print(f"Hello, {name}!")<\/p>\n
      greet()         # \u8f93\u51fa: Hello, World!<\/p>\n
      greet("Alice")  # \u8f93\u51fa: Hello, Alice!<\/p>\n
      <\/code><\/pre>\n<\/p>\n<\/li>\n<\/ol>\n
      \u4e09\u3001NONE<\/code>\u4e0e\u5f02\u5e38\u5904\u7406<\/p>\n<\/p>\n
      None<\/code>\u5728\u5f02\u5e38\u5904\u7406\u548c\u6d41\u7a0b\u63a7\u5236\u4e2d\u4e5f\u626e\u6f14\u7740\u91cd\u8981\u89d2\u8272\u3002<\/p>\n<\/p>\n
        \n
      1. \n
        \u9519\u8bef\u5904\u7406<\/strong><\/p>\n<\/p>\n
        \u5728\u67d0\u4e9b\u60c5\u51b5\u4e0b\uff0c\u51fd\u6570\u53ef\u80fd\u9047\u5230\u9519\u8bef\u6216\u5f02\u5e38\uff0c\u8fd4\u56deNone<\/code>\u8868\u793a\u65e0\u6cd5\u8fd4\u56de\u6709\u6548\u7ed3\u679c\u3002\u8fd9\u79cd\u7528\u6cd5\u901a\u5e38\u4f34\u968f\u7740\u5f02\u5e38\u7684\u6355\u83b7\uff1a<\/p>\n<\/p>\n
        def SAFe<\/a>_divide(a, b):<\/p>\n
            try:<\/p>\n
                return a \/ b<\/p>\n
            except ZeroDivisionError:<\/p>\n
                return None<\/p>\n
        result = safe_divide(10, 0)<\/p>\n
        if result is None:<\/p>\n
            print("Division by zero is not allowed.")<\/p>\n
        <\/code><\/pre>\n<\/p>\n<\/li>\n
      2. \n
        \u7f3a\u5931\u6570\u636e\u5904\u7406<\/strong><\/p>\n<\/p>\n
        \u5728\u6570\u636e\u5206\u6790\u548c\u5904\u7406\u8fc7\u7a0b\u4e2d\uff0cNone<\/code>\u53ef\u4ee5\u7528\u6765\u6807\u8bb0\u7f3a\u5931\u7684\u6570\u636e\u3002\u8bb8\u591a\u6570\u636e\u5904\u7406\u5e93\uff08\u5982Pandas\uff09\u80fd\u8bc6\u522b\u548c\u5904\u7406None<\/code>\u503c\u3002<\/p>\n<\/p>\n<\/li>\n<\/ol>\n
        \u56db\u3001NONE<\/code>\u4e0e\u9762\u5411\u5bf9\u8c61\u7f16\u7a0b<\/p>\n<\/p>\n
        \u5728\u9762\u5411\u5bf9\u8c61\u7f16\u7a0b\u4e2d\uff0cNone<\/code>\u4e5f\u6709\u5176\u91cd\u8981\u7684\u7528\u6b66\u4e4b\u5730\u3002<\/p>\n<\/p>\n
          \n
        1. \n
          \u521d\u59cb\u5316\u5bf9\u8c61\u5c5e\u6027<\/strong><\/p>\n<\/p>\n
          \u5728\u7c7b\u7684\u521d\u59cb\u5316\u65b9\u6cd5\u4e2d\uff0c\u53ef\u4ee5\u4f7f\u7528None<\/code>\u6765\u521d\u59cb\u5316\u5c5e\u6027\uff0c\u8868\u793a\u8fd9\u4e9b\u5c5e\u6027\u5c1a\u672a\u88ab\u8d4b\u503c\uff1a<\/p>\n<\/p>\n
          class MyClass:<\/p>\n
              def __init__(self):<\/p>\n
                  self.value = None<\/p>\n
          obj = MyClass()<\/p>\n
          print(obj.value)  # \u8f93\u51fa: None<\/p>\n
          <\/code><\/pre>\n<\/p>\n<\/li>\n
        2. \n
          \u65b9\u6cd5\u8fd4\u56de\u503c<\/strong><\/p>\n<\/p>\n
          \u7c7b\u65b9\u6cd5\u53ef\u4ee5\u8fd4\u56deNone<\/code>\uff0c\u8868\u793a\u64cd\u4f5c\u672a\u80fd\u6210\u529f\u6216\u6ca1\u6709\u5177\u4f53\u7ed3\u679c\uff1a<\/p>\n<\/p>\n
          class Database:<\/p>\n
              def get_record(self, record_id):<\/p>\n
                  # \u5047\u8bbe\u5728\u6570\u636e\u5e93\u4e2d\u67e5\u627e\u8bb0\u5f55<\/p>\n
                  record = self._find_in_db(record_id)<\/p>\n
                  if record is None:<\/p>\n
                      return None<\/p>\n
                  return record<\/p>\n
          <\/code><\/pre>\n<\/p>\n<\/li>\n<\/ol>\n
          \u4e94\u3001NONE<\/code>\u7684\u6ce8\u610f\u4e8b\u9879<\/p>\n<\/p>\n
          \u867d\u7136None<\/code>\u5728Python\u4e2d\u975e\u5e38\u6709\u7528\uff0c\u4f46\u4f7f\u7528\u65f6\u5e94\u6ce8\u610f\u4e00\u4e9b\u7ec6\u8282\u3002<\/p>\n<\/p>\n
            \n
          1. \n
            \u4e0e\u5e03\u5c14\u503c\u7684\u6bd4\u8f83<\/strong><\/p>\n<\/p>\n
            \u5728\u5e03\u5c14\u4e0a\u4e0b\u6587\u4e2d\uff0cNone<\/code>\u4f1a\u88ab\u89e3\u91ca\u4e3aFalse<\/code>\u3002\u8fd9\u610f\u5473\u7740\u5728\u6761\u4ef6\u5224\u65ad\u4e2d\uff0cNone<\/code>\u7b49\u6548\u4e8e\u5e03\u5c14\u503cFalse<\/code>\uff1a<\/p>\n<\/p>\n
            if not None:<\/p>\n
                print("None is False in a boolean context.")<\/p>\n
            <\/code><\/pre>\n<\/p>\n<\/li>\n
          2. \n
            \u4e0e\u7a7a\u5b57\u7b26\u4e32\u3001\u7a7a\u5217\u8868\u7684\u533a\u522b<\/strong><\/p>\n<\/p>\n
            None<\/code>\u4e0e\u7a7a\u5b57\u7b26\u4e32''<\/code>\u3001\u7a7a\u5217\u8868[]<\/code>\u7b49\u4e0d\u540c\u3002\u5b83\u4eec\u5728Python\u4e2d\u662f\u4e0d\u540c\u7684\u5bf9\u8c61\uff0cNone<\/code>\u8868\u793a\u201c\u65e0\u201d\uff0c\u800c\u7a7a\u5b57\u7b26\u4e32\u3001\u7a7a\u5217\u8868\u8868\u793a\u201c\u7a7a\u4f46\u5b58\u5728\u201d\uff1a<\/p>\n<\/p>\n
            if '' == None:<\/p>\n
                print("This will not print.")<\/p>\n
            <\/code><\/pre>\n<\/p>\n<\/li>\n
          3. \n
            \u907f\u514d\u8bef\u7528==<\/code>\u8fdb\u884c\u6bd4\u8f83<\/strong><\/p>\n<\/p>\n
            \u5728\u68c0\u67e5\u53d8\u91cf\u662f\u5426\u4e3aNone<\/code>\u65f6\uff0c\u5e94\u4f7f\u7528is<\/code>\u800c\u4e0d\u662f==<\/code>\u3002==<\/code>\u4f1a\u8fdb\u884c\u503c\u7684\u6bd4\u8f83\uff0c\u53ef\u80fd\u5bfc\u81f4\u610f\u5916\u7ed3\u679c\uff1a<\/p>\n<\/p>\n
            x = None<\/p>\n
            print(x == None)  # \u867d\u7136\u8fd4\u56deTrue\uff0c\u4f46\u4e0d\u63a8\u8350\u8fd9\u6837\u5199<\/p>\n
            print(x is None)  # \u63a8\u8350\u7528\u6cd5<\/p>\n
            <\/code><\/pre>\n<\/p>\n<\/li>\n<\/ol>\n
            \u901a\u8fc7\u8fd9\u4e9b\u8be6\u7ec6\u7684\u63a2\u8ba8\uff0c\u6211\u4eec\u53ef\u4ee5\u770b\u5230\uff0cNone<\/code>\u5728Python\u4e2d\u662f\u4e00\u4e2a\u529f\u80fd\u5f3a\u5927\u4e14\u7075\u6d3b\u7684\u5de5\u5177\uff0c\u9002\u7528\u4e8e\u591a\u4e2a\u7f16\u7a0b\u573a\u666f\u3002\u65e0\u8bba\u662f\u5728\u521d\u59cb\u5316\u53d8\u91cf\u3001\u5904\u7406\u5f02\u5e38\u3001\u8fd8\u662f\u5728\u590d\u6742\u6570\u636e\u7ed3\u6784\u4e2d\uff0c\u7406\u89e3\u548c\u6b63\u786e\u4f7f\u7528None<\/code>\u90fd\u662f\u7f16\u5199\u5065\u58eePython\u4ee3\u7801\u7684\u91cd\u8981\u4e00\u90e8\u5206\u3002<\/p>\n<\/p>\n
            \u76f8\u5173\u95ee\u7b54FAQs\uff1a<\/strong><\/h2>\n
             Python\u4e2d\u5982\u4f55\u8868\u793a\u7a7a\u503c\u6216\u7f3a\u5931\u503c\uff1f<\/strong>
            \u5728Python\u4e2d\uff0c\u7a7a\u503c\u901a\u5e38\u901a\u8fc7None<\/code>\u6765\u8868\u793a\u3002None<\/code>\u662f\u4e00\u4e2a\u7279\u6b8a\u7684\u5e38\u91cf\uff0c\u8868\u793a\u6ca1\u6709\u503c\u6216\u7a7a\u503c\u3002\u5728\u7f16\u7a0b\u65f6\uff0c\u4f60\u53ef\u4ee5\u5c06None<\/code>\u7528\u4e8e\u53d8\u91cf\u3001\u51fd\u6570\u8fd4\u56de\u503c\u7b49\u573a\u666f\uff0c\u4ee5\u6307\u793a\u7f3a\u5931\u6216\u65e0\u6548\u7684\u6570\u636e\u3002<\/p>\n
            \u5728Python\u4e2d\u5982\u4f55\u68c0\u67e5\u4e00\u4e2a\u53d8\u91cf\u662f\u5426\u4e3aNone\uff1f<\/strong>
            \u8981\u68c0\u67e5\u4e00\u4e2a\u53d8\u91cf\u662f\u5426\u4e3aNone<\/code>\uff0c\u53ef\u4ee5\u4f7f\u7528is<\/code>\u8fd0\u7b97\u7b26\u3002\u793a\u4f8b\u4ee3\u7801\u5982\u4e0b\uff1a<\/p>\n
            if variable is None:\n    print("\u53d8\u91cf\u662f\u7a7a\u503c")\n<\/code><\/pre>\n
            \u8fd9\u79cd\u65b9\u5f0f\u6bd4\u4f7f\u7528==<\/code>\u66f4\u5b89\u5168\uff0c\u56e0\u4e3ais<\/code>\u8fd0\u7b97\u7b26\u68c0\u67e5\u7684\u662f\u5bf9\u8c61\u7684\u8eab\u4efd\uff0c\u800c\u4e0d\u4ec5\u4ec5\u662f\u503c\u7684\u76f8\u7b49\u3002<\/p>\n
            \u5982\u4f55\u5728Python\u4e2d\u5904\u7406\u5305\u542bNone\u7684\u5217\u8868\u6216\u6570\u636e\u7ed3\u6784\uff1f<\/strong>
            \u5728\u5904\u7406\u5305\u542bNone<\/code>\u7684\u5217\u8868\u65f6\uff0c\u53ef\u4ee5\u4f7f\u7528\u5217\u8868\u63a8\u5bfc\u5f0f\u6216filter<\/code>\u51fd\u6570\u6765\u79fb\u9664\u7a7a\u503c\u3002\u4f8b\u5982\uff0c\u53ef\u4ee5\u4f7f\u7528\u4ee5\u4e0b\u4ee3\u7801\u6765\u8fc7\u6ee4\u6389\u5217\u8868\u4e2d\u7684None<\/code>\u503c\uff1a<\/p>\n
            filtered_list = [x for x in original_list if x is not None]\n<\/code><\/pre>\n
            \u8fd9\u79cd\u65b9\u5f0f\u53ef\u4ee5\u786e\u4fdd\u4f60\u5f97\u5230\u4e00\u4e2a\u4e0d\u5305\u542b\u7a7a\u503c\u7684\u65b0\u5217\u8868\uff0c\u65b9\u4fbf\u540e\u7eed\u7684\u6570\u636e\u5904\u7406\u548c\u5206\u6790\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"\u5728Python\u4e2d\uff0c\u8868\u793anull\u7684\u65b9\u5f0f\u662f\u4f7f\u7528None\u5173\u952e\u5b57\u3001None\u7528\u4e8e\u8868\u793a\u53d8\u91cf\u6ca1\u6709\u503c\u6216\u7a7a\u503c\u3001\u5728\u51fd\u6570\u6ca1\u6709\u8fd4\u56de\u503c\u65f6 […]","protected":false},"author":3,"featured_media":951903,"comment_status":"closed","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[37],"tags":[],"acf":[],"_links":{"self":[{"href":"https:\/\/docs.pingcode.com\/wp-json\/wp\/v2\/posts\/951897"}],"collection":[{"href":"https:\/\/docs.pingcode.com\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/docs.pingcode.com\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/docs.pingcode.com\/wp-json\/wp\/v2\/users\/3"}],"replies":[{"embeddable":true,"href":"https:\/\/docs.pingcode.com\/wp-json\/wp\/v2\/comments?post=951897"}],"version-history":[{"count":"1","href":"https:\/\/docs.pingcode.com\/wp-json\/wp\/v2\/posts\/951897\/revisions"}],"predecessor-version":[{"id":951904,"href":"https:\/\/docs.pingcode.com\/wp-json\/wp\/v2\/posts\/951897\/revisions\/951904"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/docs.pingcode.com\/wp-json\/wp\/v2\/media\/951903"}],"wp:attachment":[{"href":"https:\/\/docs.pingcode.com\/wp-json\/wp\/v2\/media?parent=951897"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/docs.pingcode.com\/wp-json\/wp\/v2\/categories?post=951897"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/docs.pingcode.com\/wp-json\/wp\/v2\/tags?post=951897"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}