exec：三个参数
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()
#!/usr/bin/env python
# -*- coding:utf-8 -*-
# Author: vita
g={
'x':1,
'y':2
}
l={}
exec('''
global x,z
x=100
z=200
m=300
''',g,l)
print(g) #{'x': 100, 'y': 2,'z':200,......}
print(l) #{'m': 300}
E:\PythonProject\python-test\venvP3\Scripts\python.exe E:/PythonProject/python-test/BasicGrammer/test.py
{'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__': , '__spec__': ModuleSpec(name='builtins', loader=), '__build_class__': , '__import__': , 'abs': , 'all': , 'any': , 'ascii': , 'bin': , 'callable': , 'chr': , 'compile': , 'delattr': , 'dir': , 'divmod': , 'eval': , 'exec': , 'format': , 'getattr': , 'globals': , 'hasattr': , 'hash': , 'hex': , 'id': , 'input': , 'isinstance': , 'issubclass': , 'iter': , 'len': , 'locals': , 'max': , 'min': , 'next': , 'oct': , 'ord': , 'pow': , 'print': , 'repr': , 'round': , 'setattr': , 'sorted': , 'sum': , 'vars': , 'None': None, 'Ellipsis': Ellipsis, 'NotImplemented': NotImplemented, 'False': False, 'True': True, 'bool': , 'memoryview': , 'bytearray': , 'bytes': , 'classmethod': , 'complex': , 'dict': , 'enumerate': , 'filter': , 'float': , 'frozenset': , 'property': , 'int': , 'list': , 'map': , 'object': , 'range': , 'reversed': , 'set': , 'slice': , 'staticmethod': , 'str': , 'super': , 'tuple': , 'type': , 'zip': , '__debug__': True, 'BaseException': , 'Exception': , 'TypeError': , 'StopAsyncIteration': , 'StopIteration': , 'GeneratorExit': , 'SystemExit': , 'KeyboardInterrupt': , 'ImportError': , 'ModuleNotFoundError': , 'OSError': , 'EnvironmentError': , 'IOError': , 'WindowsError': , 'EOFError': , 'RuntimeError': , 'RecursionError': , 'NotImplementedError': , 'NameError': , 'UnboundLocalError': , 'AttributeError': , 'SyntaxError': , 'IndentationError': , 'TabError': , 'LookupError': , 'IndexError': , 'KeyError': , 'ValueError': , 'UnicodeError': , 'UnicodeEncodeError': , 'UnicodeDecodeError': , 'UnicodeTranslateError': , 'AssertionError': , 'ArithmeticError': , 'FloatingPointError': , 'OverflowError': , 'ZeroDivisionError': , 'SystemError': , 'ReferenceError': , 'BufferError': , 'MemoryError': , 'Warning': , 'UserWarning': , 'DeprecationWarning': , 'PendingDeprecationWarning': , 'SyntaxWarning': , 'RuntimeWarning': , 'FutureWarning': , 'ImportWarning': , 'UnicodeWarning': , 'BytesWarning': , 'ResourceWarning': , 'ConnectionError': , 'BlockingIOError': , 'BrokenPipeError': , 'ChildProcessError': , 'ConnectionAbortedError': , 'ConnectionRefusedError': , 'ConnectionResetError': , 'FileExistsError': , 'FileNotFoundError': , 'IsADirectoryError': , 'NotADirectoryError': , 'InterruptedError': , 'PermissionError': , 'ProcessLookupError': , 'TimeoutError': , '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.
All Rights Reserved.
Copyright (c) 2000 BeOpen.com.
All Rights Reserved.
Copyright (c) 1995-2001 Corporation for National Research Initiatives.
All Rights Reserved.
Copyright (c) 1991-1995 Stichting Mathematisch Centrum, Amsterdam.
All Rights Reserved., 'credits': Thanks to CWI, CNRI, BeOpen.com, Zope Corporation and a cast of thousands
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}
{'m': 300}
Process finished with exit code 0
元类是用于创建类的类，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，而元类是为了控制类的创建行为
元类的实例化结果为我们用class定义的类，正如类的实例化是对象(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。
成都创新互联公司服务项目包括梨树网站建设、梨树网站制作、梨树网页制作以及梨树网络营销策划等。多年来，我们专注于互联网行业，利用自身积累的技术优势、行业经验、深度合作伙伴关系等，向广大中小型企业、政府机构等提供互联网行业的解决方案，梨树网站推广取得了明显的社会效益与经济效益。目前，我们服务的客户以成都为中心已经辐射到梨树省份的部分城市，未来相信会继续扩大服务区域并继续获得客户的支持与信任！
"方式一：使用class关键字创建的类"
class Chinese(object):
country='China'
def __init__(self,name,age):
self.name=name
self.age=age
def talk(self):
print('%s is talking' %self.name)"方式二：使用type创建类"
#准备工作：
type(class_name,class_bases,class_dic)
#type创建类主要分为三部分
1 类名===class_name
2 类的父类===class_bases
3 类体===class_dic==即类的内容，可使用exec产生
#!/usr/bin/env python
# -*- coding:utf-8 -*-
# Author: vita
#类名
class_name='Chinese'
#类的父类
class_bases=(object,)
#类体
class_body="""
country='China'
def __init__(self,name,age):
self.name=name
self.age=age
def talk(self):
print('%s is talking' %self.name)
"""
#步骤一（先处理类体->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），
# 我们可以事先定义一个空字典，
# 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
class_dic={}
exec(class_body,globals(),class_dic)
print("class_dic===",class_dic)
# 步骤二：调用元类type（也可以自定义）来产生类Chinense
Foo=type(class_name,class_bases,class_dic) #实例化type得到对象Foo，即我们用class定义的类Foo
print(Foo)
print(type(Foo))
print(isinstance(Foo,type))
print(Foo.__dict__)
E:\PythonProject\python-test\venvP3\Scripts\python.exe E:/PythonProject/python-test/BasicGrammer/test.py
class_dic=== {'country': 'China', '__init__': , 'talk': }
True
{'country': 'China', '__init__': , 'talk': , '__module__': '__main__', '__dict__': , '__weakref__': , '__doc__': None}
Process finished with exit code 0
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
"定义类的时候，就会自动运行Mymeta了"
#!/usr/bin/env python
# -*- coding:utf-8 -*-
# Author: vita
class Mymeta(type):
def __init__(self,class_name,class_bases,class_dic):
print("metadata") #验证定义类的时候就运行了该类
if not class_name.istitle():
raise TypeError('类名的首字母必须大写')
if '__doc__' not in class_dic or not class_dic['__doc__'].strip():
raise TypeError('必须有注释，且注释不能为空')
super(Mymeta,self).__init__(class_name,class_bases,class_dic)
class Chinese(object,metaclass=Mymeta):
'''
中文人的类
'''
country='China'
def __init__(self,namem,age):
self.name=namem
self.age=age
def talk(self):
print('%s is talking' %self.name)
E:\PythonProject\python-test\venvP3\Scripts\python.exe E:/PythonProject/python-test/BasicGrammer/test.py
metadata
Process finished with exit code 0
"类名改为小写，运行"
#!/usr/bin/env python
# -*- coding:utf-8 -*-
# Author: vita
class Mymeta(type):
def __init__(self,class_name,class_bases,class_dic):
print("metadata")
if not class_name.istitle():
raise TypeError('类名的首字母必须大写')
if '__doc__' not in class_dic or not class_dic['__doc__'].strip():
raise TypeError('必须有注释，且注释不能为空')
super(Mymeta,self).__init__(class_name,class_bases,class_dic)
class chinese(object,metaclass=Mymeta):
'''
中文人的类
'''
country='China'
def __init__(self,namem,age):
self.name=namem
self.age=age
def talk(self):
print('%s is talking' %self.name)
E:\PythonProject\python-test\venvP3\Scripts\python.exe E:/PythonProject/python-test/BasicGrammer/test.py
metadata
Traceback (most recent call last):
File "E:/PythonProject/python-test/BasicGrammer/test.py", line 15, in
class chinese(object,metaclass=Mymeta):
File "E:/PythonProject/python-test/BasicGrammer/test.py", line 8, in __init__
raise TypeError('类名的首字母必须大写')
TypeError: 类名的首字母必须大写
Process finished with exit code 1
"验证没有注释时的情况"
#!/usr/bin/env python
# -*- coding:utf-8 -*-
# Author: vita
class Mymeta(type):
def __init__(self,class_name,class_bases,class_dic):
print("metadata")
if not class_name.istitle():
raise TypeError('类名的首字母必须大写')
if '__doc__' not in class_dic or not class_dic['__doc__'].strip():
raise TypeError('必须有注释，且注释不能为空')
super(Mymeta,self).__init__(class_name,class_bases,class_dic)
class Chinese(object,metaclass=Mymeta):
country='China'
def __init__(self,namem,age):
self.name=namem
self.age=age
def talk(self):
print('%s is talking' %self.name)
E:\PythonProject\python-test\venvP3\Scripts\python.exe E:/PythonProject/python-test/BasicGrammer/test.py
metadata
Traceback (most recent call last):
File "E:/PythonProject/python-test/BasicGrammer/test.py", line 15, in
class Chinese(object,metaclass=Mymeta):
File "E:/PythonProject/python-test/BasicGrammer/test.py", line 11, in __init__
raise TypeError('必须有注释，且注释不能为空')
TypeError: 必须有注释，且注释不能为空
Process finished with exit code 1
"调用obj对象时，调用__call__方法"
#!/usr/bin/env python
# -*- coding:utf-8 -*-
# Author: vita
#知识储备__call__方法
class Foo:
var = "var"
def __call__(self, *args, **kwargs):
print(self)
print(args)
print(kwargs)
obj=Foo()
# print(obj.var) 这样不会调用__call__
#调用obj对象时，调用__call__方法
obj(1,2,3,a=1,b=2,c=3) #obj.__call__(obj,1,2,3,a=1,b=2,c=3)
#元类内部也应有有一个__call__方法，会在调用Foo时触发执行
#Foo(1,2,x=1) #Foo.__call__(Foo,1,2,x=1)#!/usr/bin/env python
# -*- coding:utf-8 -*-
# Author: vita
class Mymeta(type):
def __init__(self,class_name,class_bases,class_dic):
if not class_name.istitle():
raise TypeError('类名的首字母必须大写')
if '__doc__' not in class_dic or not class_dic['__doc__'].strip():
raise TypeError('必须有注释，且注释不能为空')
super(Mymeta,self).__init__(class_name,class_bases,class_dic)
def __call__(self, *args, **kwargs): #obj=Chinese('egon',age=18)
print("exec __call__")
#第一件事：先造一个空对象obj
obj=object.__new__(self)
#第二件事：初始化obj
self.__init__(obj,*args,**kwargs)
#第三件事：返回obj
return obj
class Chinese(object,metaclass=Mymeta):
'''
中文人的类
'''
country='China'
def __init__(self,namem,age):
self.name=namem
self.age=age
def talk(self):
print('%s is talking' %self.name)
obj=Chinese('egon',age=18) #Chinese.__call__(Chinese,'egon',18)
print(obj.__dict__)
E:\PythonProject\python-test\venvP3\Scripts\python.exe E:/PythonProject/python-test/BasicGrammer/test.py
exec __call__
{'name': 'egon', 'age': 18}
Process finished with exit code 0
"#!/usr/bin/env python
# -*- coding:utf-8 -*-
# Author: vita
#单例模式
#实现方式一：
class MySQL:
__instance=None #__instance=obj1
def __init__(self):
self.host='127.0.0.1'
self.port=3306
@classmethod
def singleton(cls):
if not cls.__instance:
obj=cls()
cls.__instance=obj
return cls.__instance
#三个对象都是一个，因为只创建了一次
obj1=MySQL.singleton()
obj2=MySQL.singleton()
obj3=MySQL.singleton()
print(obj1 is obj2 is obj3)
"
E:\PythonProject\python-test\venvP3\Scripts\python.exe E:/PythonProject/python-test/BasicGrammer/test.py
True
Process finished with exit code 0
#!/usr/bin/env python
# -*- coding:utf-8 -*-
# Author: vita
#单例模式
#实现方式二：元类的方式
class Mymeta(type):
def __init__(self,class_name,class_bases,class_dic):
if not class_name.istitle():
raise TypeError('类名的首字母必须大写')
if '__doc__' not in class_dic or not class_dic['__doc__'].strip():
raise TypeError('必须有注释，且注释不能为空')
super(Mymeta,self).__init__(class_name,class_bases,class_dic)
self.__instance=None
def __call__(self, *args, **kwargs): #obj=Chinese('egon',age=18)
if not self.__instance:
obj=object.__new__(self)
self.__init__(obj)
self.__instance=obj
return self.__instance
class Mysql(object,metaclass=Mymeta):
'''
mysql xxx
'''
def __init__(self):
self.host='127.0.0.1'
self.port=3306
obj1=Mysql()
obj2=Mysql()
obj3=Mysql()
print(obj1 is obj2 is obj3)
E:\PythonProject\python-test\venvP3\Scripts\python.exe E:/PythonProject/python-test/BasicGrammer/test.py
True
Process finished with exit code 0