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  • [课程章节]第2-1节:python语法关键字、内置类型与内置函数
  • 发布: 江湖程序员 来源: 本站原创 时间: 2023/11/12 16:07
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    第01-2节:python语法关键字、内置类型与内置函数
    如何高效地学习python语言?.mp4
      相信绝大多数初学者都会有这样一种疑惑,学习python编程要学的语法有哪些?要学的内置函数和类型有哪些?该如何去学?下面我用代码列出全部:
    一、python语法关键字(共35个),敲以下代码运行即可输出:
    print(__import__('keyword').kwlist)
    输出结果:
    ['False', 'None', 'True', 'and', 'as', 'assert', 'async', 'await', 'break', 'class', 'continue', 'def', 'del', 'elif', 'else', 'except', 'finally', 'for', 'from', 'global', 'if', 'import', 'in', 'is', 'lambda', 'nonlocal', 'not', 'or', 'pass', 'raise', 'return', 'try', 'while', 'with', 'yield']
    >>>
    析:在实际编写的代码中python语法关键字是不带引号的,但用help(...)方法查看使用说明书时则须带上引号,
    例如:
    help('import')
    输出结果:
    The "import" statement
    **********************
       import_stmt     ::= "import" module ["as" identifier] ("," module ["as" identifier])*
                       | "from" relative_module "import" identifier ["as" identifier]
                       ("," identifier ["as" identifier])*
                       | "from" relative_module "import" "(" identifier ["as" identifier]
                       ("," identifier ["as" identifier])* [","] ")"
                       | "from" module "import" "*"
       module          ::= (identifier ".")* identifier
       relative_module ::= "."* module | "."+
    ...
    Examples:
       import foo                 # foo imported and bound locally
       import foo.bar.baz         # foo.bar.baz imported, foo bound locally
       import foo.bar.baz as fbb  # foo.bar.baz imported and bound as fbb
       from foo.bar import baz    # foo.bar.baz imported and bound as baz
       from foo import attr       # foo imported and foo.attr bound as attr
    ...
    >>>
    二、python自带类型与函数(共154个),敲以下代码运行即可输出:
    print((lambda D:[D.__setitem__(i, eval(i)) for i in dir(__builtins__)] and D)(dict()))
    或:
    print((lambda D:[D.__setitem__(i, type(i)) for i in dir(__builtins__)] and D)(dict()))
    输出结果:
    {'ArithmeticError': , 'AssertionError': , 'AttributeError': , 'BaseException': , 'BlockingIOError': , 'BrokenPipeError': , 'BufferError': , 'BytesWarning': , 'ChildProcessError': , 'ConnectionAbortedError': , 'ConnectionError': , 'ConnectionRefusedError': , 'ConnectionResetError': , 'DeprecationWarning': , 'EOFError': , 'Ellipsis': , 'EnvironmentError': , 'Exception': , 'False': , 'FileExistsError': , 'FileNotFoundError': , 'FloatingPointError': , 'FutureWarning': , 'GeneratorExit': , 'IOError': , 'ImportError': , 'ImportWarning': , 'IndentationError': , 'IndexError': , 'InterruptedError': , 'IsADirectoryError': , 'KeyError': , 'KeyboardInterrupt': , 'LookupError': , 'MemoryError': , 'ModuleNotFoundError': , 'NameError': , 'None': , 'NotADirectoryError': , 'NotImplemented': , 'NotImplementedError': , 'OSError': , 'OverflowError': , 'PendingDeprecationWarning': , 'PermissionError': , 'ProcessLookupError': , 'RecursionError': , 'ReferenceError': , 'ResourceWarning': , 'RuntimeError': , 'RuntimeWarning': , 'StopAsyncIteration': , 'StopIteration': , 'SyntaxError': , 'SyntaxWarning': , 'SystemError': , 'SystemExit': , 'TabError': , 'TimeoutError': , 'True': , 'TypeError': , 'UnboundLocalError': , 'UnicodeDecodeError': , 'UnicodeEncodeError': , 'UnicodeError': , 'UnicodeTranslateError': , 'UnicodeWarning': , 'UserWarning': , 'ValueError': , 'Warning': , 'WindowsError': , 'ZeroDivisionError': , '__build_class__': , '__debug__': , '__doc__': , '__import__': , '__loader__': , '__name__': , '__package__': , '__spec__': , 'abs': , 'all': , 'any': , 'ascii': , 'bin': , 'bool': , 'bytearray': , 'bytes': , 'callable': , 'chr': , 'classmethod': , 'compile': , 'complex': , 'copyright': , 'credits': , 'delattr': , 'dict': , 'dir': , 'divmod': , 'enumerate': , 'eval': , 'exec': , 'exit': , 'filter': , 'float': , 'format': , 'frozenset': , 'getattr': , 'globals': , 'hasattr': , 'hash': , 'help': , 'hex': , 'id': , 'input': , 'int': , 'isinstance': , 'issubclass': , 'iter': , 'len': , 'license': , 'list': , 'locals': , 'map': , 'max': , 'memoryview': , 'min': , 'next': , 'object': , 'oct': , 'open': , 'ord': , 'pow': , 'print': , 'property': , 'quit': , 'range': , 'repr': , 'reversed': , 'round': , 'set': , 'setattr': , 'slice': , 'sorted': , 'staticmethod': , 'str': , 'sum': , 'super': , 'tuple': , 'type': , 'vars': , 'zip': }
    >>>
    析:在实际编写的代码中python自带类型与函数名称皆不带引号的,用help(...)方法可以查看自带类型或函数的使用说明书,
    例如:
    help(list)
    输出结果:
    Help on class list in module builtins:
    class list(object)
     |  list(iterable=(), /)
     |  Built-in mutable sequence.
     |  If no argument is given, the constructor creates a new empty list.
     |  The argument must be an iterable if specified.
     |  Methods defined here:
     |  __add__(self, value, /)
     |      Return self+value.
     |  __contains__(self, key, /)
     |      Return key in self.
     |  __delitem__(self, key, /)
     |      Delete self[key].
     |  __eq__(self, value, /)
     |      Return self==value.
     |  __ge__(self, value, /)
     |      Return self>=value.
     |  __getattribute__(self, name, /)
     |      Return getattr(self, name).
     |  __getitem__(...)
     |      x.__getitem__(y) <==> x[y]
     |  __gt__(self, value, /)
     |      Return self>value.
     |  __iadd__(self, value, /)
     |      Implement self+=value.
     |  __imul__(self, value, /)
     |      Implement self*=value.
     |  __init__(self, /, *args, **kwargs)
     |      Initialize self.  See help(type(self)) for accurate signature.
     |  __iter__(self, /)
     |      Implement iter(self).
     |  __le__(self, value, /)
     |      Return self<=value.
     |  __len__(self, /)
     |      Return len(self).
     |  __lt__(self, value, /)
     |      Return self<value.
     |  __mul__(self, value, /)
     |      Return self*value.
     |  __ne__(self, value, /)
     |      Return self!=value.
     |  __repr__(self, /)
     |      Return repr(self).
     |  __reversed__(self, /)
     |      Return a reverse iterator over the list.
     |  __rmul__(self, value, /)
     |      Return value*self.
     |  __setitem__(self, key, value, /)
     |      Set self[key] to value.
     |  __sizeof__(self, /)
     |      Return the size of the list in memory, in bytes.
     |  append(self, object, /)
     |      Append object to the end of the list.
     |  clear(self, /)
     |      Remove all items from list.
     |  copy(self, /)
     |      Return a shallow copy of the list.
     |  count(self, value, /)
     |      Return number of occurrences of value.
     |  extend(self, iterable, /)
     |      Extend list by appending elements from the iterable.
     |  index(self, value, start=0, stop=9223372036854775807, /)
     |      Return first index of value.
     |      Raises ValueError if the value is not present.
     |  insert(self, index, object, /)
     |      Insert object before index.
     |  pop(self, index=-1, /)
     |      Remove and return item at index (default last).
     |      Raises IndexError if list is empty or index is out of range.
     |  remove(self, value, /)
     |      Remove first occurrence of value.
     |      Raises ValueError if the value is not present.
     |  reverse(self, /)
     |      Reverse *IN PLACE*.
     |  sort(self, /, *, key=None, reverse=False)
     |      Sort the list in ascending order and return None.
     |      The sort is in-place (i.e. the list itself is modified) and stable (i.e. the
     |      order of two equal elements is maintained).
     |      If a key function is given, apply it once to each list item and sort them,
     |      ascending or descending, according to their function values.
     |      The reverse flag can be set to sort in descending order.
     |  ----------------------------------------------------------------------
     |  Static methods defined here:
     |  __new__(*args, **kwargs) from builtins.type
     |      Create and return a new object.  See help(type) for accurate signature.
     |  ----------------------------------------------------------------------
     |  Data and other attributes defined here:
     |  __hash__ = None#__hash__方法为None的类型为可变类型、否则为不可变类型
     >>>
    析:list类型,即列表类型,可见__hash__ = None,所以列表类型是可变类型,在实际编写代码的列表对象形式为:
    a = ['good', 520, '中国', 3.14159265]#这是列表类型的一个实例对象称之为列表对象(python中一切皆对象,对象即实例对象,python中默认每种类型皆可多次实例化,动态产生出多个实例对象)
    列表对象的特点:前后方括号、中间每个元素以小写逗号分隔、可变类型、不可哈希。
    上面这行代码中,等号前面的“a”为变量,写代码定义变量是为了便于追踪引用某个对象,变量的特点是以字母或“_”(下划线)开头,只能是由字母、下划线和数字组成。
    代码后面的#号为标记注释,在代码中所编写的注释前要加上#号,代码中的注释不会影响代码的运行。

    分别运行以下代码,即可分别输出常用类型的使用说明书:
    help(str)#字符串类型
    help(dict)#字典类型
    help(tuple)#元组类型
    help(set)#集合类型
    help(int)#整数类型
    help(float)#浮点数类型

    作者:江湖程序员 (python帮助网)
    转载请注明出处: www.pythonhelp.cn


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