1.exec
1 exec(source, globals=None, locals=None, /) 2 Execute the given source in the context of globals and locals. 3 4 The source may be a string representing one or more Python statements 5 or a code object as returned by compile(). 6 The globals must be a dictionary and locals can be any mapping, 7 defaulting to the current globals and locals. 8 If only globals is given, locals defaults to it.
- 参数一：字符串形式的命令
- 参数二：全局作用域（字典形式），如果不指定，默认为globals()
- 参数三：局部作用域（字典形式），如果不指定，默认为locals()
1 s = """ 2 global x,z 3 x = 100 4 z = 200 5 6 m = 300 7 """ 8 g = {‘x‘:1,‘y‘:2} 9 l = {} 10 exec(s,g,l) 11 # print(g) 12 #{‘x‘: 100, ‘y‘: 2, ‘__builtins__‘: {‘__name__‘: ‘builtins‘, ‘__doc__‘: "Built-in functions, exceptions, and other objects.\n\nNoteworthy: None is the `nil‘ object; Ellipsis represents `...‘ in slices.", ‘__package__‘: ‘‘, ‘__loader__‘: <class ‘_frozen_importlib.BuiltinImporter‘>, ‘__spec__‘: ModuleSpec(name=‘builtins‘, loader=<class ‘_frozen_importlib.BuiltinImporter‘>), ‘__build_class__‘: <built-in function __build_class__>, ‘__import__‘: <built-in function __import__>, ‘abs‘: <built-in function abs>, ‘all‘: <built-in function all>, ‘any‘: <built-in function any>, ‘ascii‘: <built-in function ascii>, ‘bin‘: <built-in function bin>, ‘callable‘: <built-in function callable>, ‘chr‘: <built-in function chr>, ‘compile‘: <built-in function compile>, ‘delattr‘: <built-in function delattr>, ‘dir‘: <built-in function dir>, ‘divmod‘: <built-in function divmod>, ‘eval‘: <built-in function eval>, ‘exec‘: <built-in function exec>, ‘format‘: <built-in function format>, ‘getattr‘: <built-in function getattr>, ‘globals‘: <built-in function globals>, ‘hasattr‘: <built-in function hasattr>, ‘hash‘: <built-in function hash>, ‘hex‘: <built-in function hex>, ‘id‘: <built-in function id>, ‘input‘: <built-in function input>, ‘isinstance‘: <built-in function isinstance>, ‘issubclass‘: <built-in function issubclass>, ‘iter‘: <built-in function iter>, ‘len‘: <built-in function len>, ‘locals‘: <built-in function locals>, ‘max‘: <built-in function max>, ‘min‘: <built-in function min>, ‘next‘: <built-in function next>, ‘oct‘: <built-in function oct>, ‘ord‘: <built-in function ord>, ‘pow‘: <built-in function pow>, ‘print‘: <built-in function print>, ‘repr‘: <built-in function repr>, ‘round‘: <built-in function round>, ‘setattr‘: <built-in function setattr>, ‘sorted‘: <built-in function sorted>, ‘sum‘: <built-in function sum>, ‘vars‘: <built-in function vars>, ‘None‘: None, ‘Ellipsis‘: Ellipsis, ‘NotImplemented‘: NotImplemented, ‘False‘: False, ‘True‘: True, ‘bool‘: <class ‘bool‘>, ‘memoryview‘: <class ‘memoryview‘>, ‘bytearray‘: <class ‘bytearray‘>, ‘bytes‘: <class ‘bytes‘>, ‘classmethod‘: <class ‘classmethod‘>, ‘complex‘: <class ‘complex‘>, ‘dict‘: <class ‘dict‘>, ‘enumerate‘: <class ‘enumerate‘>, ‘filter‘: <class ‘filter‘>, ‘float‘: <class ‘float‘>, ‘frozenset‘: <class ‘frozenset‘>, ‘property‘: <class ‘property‘>, ‘int‘: <class ‘int‘>, ‘list‘: <class ‘list‘>, ‘map‘: <class ‘map‘>, ‘object‘: <class ‘object‘>, ‘range‘: <class ‘range‘>, ‘reversed‘: <class ‘reversed‘>, ‘set‘: <class ‘set‘>, ‘slice‘: <class ‘slice‘>, ‘staticmethod‘: <class ‘staticmethod‘>, ‘str‘: <class ‘str‘>, ‘super‘: <class ‘super‘>, ‘tuple‘: <class ‘tuple‘>, ‘type‘: <class ‘type‘>, ‘zip‘: <class ‘zip‘>, ‘__debug__‘: True, ‘BaseException‘: <class ‘BaseException‘>, ‘Exception‘: <class ‘Exception‘>, ‘TypeError‘: <class ‘TypeError‘>, ‘StopAsyncIteration‘: <class ‘StopAsyncIteration‘>, ‘StopIteration‘: <class ‘StopIteration‘>, ‘GeneratorExit‘: <class ‘GeneratorExit‘>, ‘SystemExit‘: <class ‘SystemExit‘>, ‘KeyboardInterrupt‘: <class ‘KeyboardInterrupt‘>, ‘ImportError‘: <class ‘ImportError‘>, ‘ModuleNotFoundError‘: <class ‘ModuleNotFoundError‘>, ‘OSError‘: <class ‘OSError‘>, ‘EnvironmentError‘: <class ‘OSError‘>, ‘IOError‘: <class ‘OSError‘>, ‘WindowsError‘: <class ‘OSError‘>, ‘EOFError‘: <class ‘EOFError‘>, ‘RuntimeError‘: <class ‘RuntimeError‘>, ‘RecursionError‘: <class ‘RecursionError‘>, ‘NotImplementedError‘: <class ‘NotImplementedError‘>, ‘NameError‘: <class ‘NameError‘>, ‘UnboundLocalError‘: <class ‘UnboundLocalError‘>, ‘AttributeError‘: <class ‘AttributeError‘>, ‘SyntaxError‘: <class ‘SyntaxError‘>, ‘IndentationError‘: <class ‘IndentationError‘>, ‘TabError‘: <class ‘TabError‘>, ‘LookupError‘: <class ‘LookupError‘>, ‘IndexError‘: <class ‘IndexError‘>, ‘KeyError‘: <class ‘KeyError‘>, ‘ValueError‘: <class ‘ValueError‘>, ‘UnicodeError‘: <class ‘UnicodeError‘>, ‘UnicodeEncodeError‘: <class ‘UnicodeEncodeError‘>, ‘UnicodeDecodeError‘: <class ‘UnicodeDecodeError‘>, ‘UnicodeTranslateError‘: <class ‘UnicodeTranslateError‘>, ‘AssertionError‘: <class ‘AssertionError‘>, ‘ArithmeticError‘: <class ‘ArithmeticError‘>, ‘FloatingPointError‘: <class ‘FloatingPointError‘>, ‘OverflowError‘: <class ‘OverflowError‘>, ‘ZeroDivisionError‘: <class ‘ZeroDivisionError‘>, ‘SystemError‘: <class ‘SystemError‘>, ‘ReferenceError‘: <class ‘ReferenceError‘>, ‘BufferError‘: <class ‘BufferError‘>, ‘MemoryError‘: <class ‘MemoryError‘>, ‘Warning‘: <class ‘Warning‘>, ‘UserWarning‘: <class ‘UserWarning‘>, ‘DeprecationWarning‘: <class ‘DeprecationWarning‘>, ‘PendingDeprecationWarning‘: <class ‘PendingDeprecationWarning‘>, ‘SyntaxWarning‘: <class ‘SyntaxWarning‘>, ‘RuntimeWarning‘: <class ‘RuntimeWarning‘>, ‘FutureWarning‘: <class ‘FutureWarning‘>, ‘ImportWarning‘: <class ‘ImportWarning‘>, ‘UnicodeWarning‘: <class ‘UnicodeWarning‘>, ‘BytesWarning‘: <class ‘BytesWarning‘>, ‘ResourceWarning‘: <class ‘ResourceWarning‘>, ‘ConnectionError‘: <class ‘ConnectionError‘>, ‘BlockingIOError‘: <class ‘BlockingIOError‘>, ‘BrokenPipeError‘: <class ‘BrokenPipeError‘>, ‘ChildProcessError‘: <class ‘ChildProcessError‘>, ‘ConnectionAbortedError‘: <class ‘ConnectionAbortedError‘>, ‘ConnectionRefusedError‘: <class ‘ConnectionRefusedError‘>, ‘ConnectionResetError‘: <class ‘ConnectionResetError‘>, ‘FileExistsError‘: <class ‘FileExistsError‘>, ‘FileNotFoundError‘: <class ‘FileNotFoundError‘>, ‘IsADirectoryError‘: <class ‘IsADirectoryError‘>, ‘NotADirectoryError‘: <class ‘NotADirectoryError‘>, ‘InterruptedError‘: <class ‘InterruptedError‘>, ‘PermissionError‘: <class ‘PermissionError‘>, ‘ProcessLookupError‘: <class ‘ProcessLookupError‘>, ‘TimeoutError‘: <class ‘TimeoutError‘>, ‘open‘: <built-in function open>, ‘quit‘: Use quit() or Ctrl-Z plus Return to exit, ‘exit‘: Use exit() or Ctrl-Z plus Return to exit, ‘copyright‘: Copyright (c) 2001-2017 Python Software Foundation. 13 # All Rights Reserved. 14 # 15 # Copyright (c) 2000 BeOpen.com. 16 # All Rights Reserved. 17 # 18 # Copyright (c) 1995-2001 Corporation for National Research Initiatives. 19 # All Rights Reserved. 20 # 21 # Copyright (c) 1991-1995 Stichting Mathematisch Centrum, Amsterdam. 22 # All Rights Reserved., ‘credits‘: Thanks to CWI, CNRI, BeOpen.com, Zope Corporation and a cast of thousands 23 # for supporting Python development. See www.python.org for more information., ‘license‘: Type license() to see the full license text, ‘help‘: Type help() for interactive help, or help(object) for help about object.}, ‘z‘: 200} 24 25 print(l) 26 #{‘m‘: 300}
2.类也是对象
- python中一切皆对象，类本身也是一个对象，可以将类当作一个对象去使用，同样满足第一类对象的概念
- 把类赋值给一个变量
- 把类作为函数参数进行传递
- 把类作为函数的返回值
- 在运行时动态地创建类
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1 class Foo: 2 pass 3 f1 = Foo()#f1是通过Foo类实例化的对象 4 print(type(f1))#<class ‘__main__.Foo‘> 5 print(type(Foo))#<class ‘type‘> 类（对象）Foo是由type类实例化而来
3.元类
- 元类是类的类，是类的模板
- 元类是用来控制如何创建类的，正如类是创建对象的模板一样，而元类的主要目的是为了控制类的创建行为
- 元类的实例化的结果是我们用class 定义的类，正如类的实例为对象（f1对象是Foo类的一个实例，Foo类是type类的一个实例）
- type是python的一个内建元类，用来直接控制生成类，python中任何class定义的类其实都是type类实例化的对象
4.创建类的两种方式
- 方式一：使用class关键字
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View Code
1 class Chinese(object): 2 country=‘China‘ 3 def __init__(self,name,age): 4 self.name=name 5 self.age=age 6 def talk(self): 7 print(‘%s is talking‘ %self.name) 8 # print(Chinese.__dict__) 9 # {‘country‘: ‘China‘, ‘__init__‘: <function __init__ at 0x0000000002062E18>, ‘talk‘: <function talk at 0x00000000021D4048>,...} 10 # print(Chinese) 11 # <class ‘__main__.Chinese‘>
- 方式二：手动模拟class创建类的过程：将创建类的步骤拆分开，手动去创建
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View Code
1 #创建类的步骤 2 #1.类名 3 #2.类的父类,默认是object 4 #3.类体 5 6 #1.类名 7 class_name = ‘Chinese‘ 8 #2.类的父类,默认是object 9 class_bases = (object,) 10 #3.类体 11 class_body = """ 12 country=‘China‘ 13 def __init__(self,name,age): 14 self.name=name 15 self.age=age 16 def talk(self): 17 print(‘%s is talking‘ %self.name) 18 """ 19 #步骤一：把类体 -> 名称空间：类体定义的名字都会存放于类的名称空间中（一个局部的名称空间）， 20 # 我们可以事先定义好一个空字典，然后用exec去执行类体的代码（exec产生名称空间的过程 21 # 与真正的class过程类似，只是后者会将__开头的属性变形），生成类的局部名称空间，即填充字典 22 class_dic = {} 23 exec(class_body,globals(),class_dic) 24 # print(class_dic) 25 #{‘country‘: ‘China‘, ‘__init__‘: <function __init__ at 0x00000000004D2E18>, ‘talk‘: <function talk at 0x00000000028A4048>} 26 27 #步骤二：调用元类type（也可以自定义）来产生类Chinese 28 # 定义类的三要素：类名，类的基类们，类的名称空间 29 Chinese = type(class_name,class_bases,class_dic) 30 # print(Chinese.__dict__) 31 # {‘country‘: ‘China‘, ‘__init__‘: <function __init__ at 0x0000000002062E18>, ‘talk‘: <function talk at 0x00000000021D4048>,...} 32 # print(Chinese) 33 #<class ‘__main__.Chinese‘> 34 obj = Chinese(‘egon‘,18) 35 # print(obj) 36 # <__main__.Chinese object at 0x000000000216AE80> 37 # print(obj.__dict__) 38 # {‘name‘: ‘egon‘, ‘age‘: 18}
5.自定义元类控制类的行为
- 一个类没有声明自己的元类，默认他的元类就是type，除了使用元类type，用户也可以通过继承type来自定义元类
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步骤一
1 #！！！如果你拷贝不注明出处的话，以后老子都不写了！！！ 2 #知识储备： 3 #产生的新对象 = object.__new__(继承object类的子类) 4 #步骤一：如果说People=type(类名,类的父类们,类的名称空间)，那么我们定义元类如下，来控制类的创建 5 class Mymeta(type): # 继承默认元类的一堆属性 6 def __init__(self, class_name, class_bases, class_dic): 7 if ‘__doc__‘ not in class_dic or not class_dic.get(‘__doc__‘).strip(): 8 raise TypeError(‘必须为类指定文档注释‘) 9 if not class_name.istitle(): 10 raise TypeError(‘类名首字母必须大写‘) 11 super(Mymeta, self).__init__(class_name, class_bases, class_dic) 12 class Chinese(object, metaclass=Mymeta):#metaclass=Mymeta不写这个的话，默认为type 13 """ 14 .... 15 """ 16 country = ‘China‘ 17 def __init__(self, name, age): 18 self.name = name 19 self.age = age 20 def talk(self): 21 print(‘%s is talking‘ % self.name)
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步骤二
1 #知识储备：__call__方法 2 # class Foo: 3 # pass 4 # obj=Foo() 5 # obj()#报错，‘Foo‘ object is not callable 6 class Foo: 7 def __init__(self, name, age): 8 self.name = name 9 self.age = age 10 def __call__(self, *args, **kwargs): 11 print(self) 12 print(args) 13 print(kwargs) 14 obj=Foo() 15 # obj()#对象在调用时会触发obj.__call__(obj, *args, **kwargs) 16 # <__main__.Foo object at 0x00000000022EA240> 17 # () 18 # {} 19 obj(1,2,3,a = 1,b = 2,c = 3)#obj.__call__(obj,1,2,3,a = 1,b = 2,c = 3) 20 # <__main__.Foo object at 0x00000000021BA240> 21 # (1, 2, 3) 22 # {‘a‘: 1, ‘b‘: 2, ‘c‘: 3}
步骤三1 class Mymeta(type): # 继承默认元类的一堆属性 2 def __init__(self, class_name, class_bases, class_dic): 3 if ‘__doc__‘ not in class_dic or not class_dic.get(‘__doc__‘).strip(): 4 raise TypeError(‘必须为类指定文档注释‘) 5 if not class_name.istitle(): 6 raise TypeError(‘类名首字母必须大写‘) 7 super(Mymeta, self).__init__(class_name, class_bases, class_dic) 8 def __call__(self, *args, **kwargs): 9 # print(self) 10 # print(args) 11 # print(kwargs) 12 #第一件事：先造一个空对象obj 13 obj = object.__new__(self) 14 #第二件事：初始化obj 15 self.__init__(obj, *args, **kwargs) 16 #第三件事：返回obj 17 return obj 18 class Chinese(object, metaclass=Mymeta):#metaclass=Mymeta不写这个的话，默认为type 19 """ ....""" 20 country = ‘China‘ 21 def __init__(self, name, age): 22 self.name = name 23 self.age = age 24 def talk(self): 25 print(‘%s is talking‘ % self.name) 26 obj = Chinese(‘egon‘,age = 18)#Chinese.__call__(Chinese,‘egon‘,18) 27 print(obj.__dict__) 28 #{‘name‘: ‘egon‘, ‘age‘: 18} 29 #如果__call__中没有做那三件事的话，执行print(obj.__dict__)是会报错的
单例模式1 #单例模式 2 # class mysql: 3 # def __init__(self): 4 # self.host = ‘127.0.0.1‘ 5 # self.port = 3306 6 # obj1 = MySQL() 7 # obj2 = MySQL() 8 # obj3 = MySQL() 9 # print(id(obj1))#35368464 10 # print(id(obj2))#35414088 11 # print(id(obj3))#35414256 12 class MySQL: 13 __instance = None 14 def __init__(self): 15 self.host = ‘127.0.0.1‘ 16 self.port = 3306 17 @classmethod 18 def singleton(cls): 19 if not cls.__instance: 20 obj = cls() 21 cls.__instance = obj 22 return cls.__instance 23 obj1 = MySQL.singleton() 24 obj2 = MySQL.singleton() 25 obj3 = MySQL.singleton() 26 print(id(obj1))#35434112 27 print(id(obj2))#35434112 28 print(id(obj3))#35434112
步骤五1 class Mymeta(type): 2 def __init__(self, class_name, class_bases, class_dic): 3 if ‘__doc__‘ not in class_dic or not class_dic.get(‘__doc__‘).strip(): 4 raise TypeError(‘必须为类指定文档注释‘) 5 if not class_name.istitle(): 6 raise TypeError(‘类名首字母必须大写‘) 7 super(Mymeta, self).__init__(class_name, class_bases, class_dic) 8 self.__instance = None 9 def __call__(self, *args, **kwargs): 10 if not self.__instance: 11 obj = object.__new__(self) 12 self.__init__(obj) 13 self.__instance = obj 14 return self.__instance 15 16 class Mysql(object,metaclass=Mymeta): 17 """....""" 18 def __init__(self): 19 self.host = ‘127.0.0.1‘ 20 self.port = 3306 21 22 obj1 = Mysql() 23 obj2 = Mysql() 24 obj3 = Mysql() 25 print(obj1 is obj2 is obj3)#True 26 print(id(obj1))#32006944 27 print(id(obj2))#32006944 28 print(id(obj3))#32006944