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万字干货，Python语法大合集，一篇文章带你入门( 八 )

Python语法

可以使用as给模块内的方法或者类起别名：
# You can shorten module namesimport math as mmath.sqrt(16) == m.sqrt(16)# => True复制代码我们可以使用dir查看我们用的模块的路径：
# You can find out which functions and attributes# are defined in a module.import mathdir(math)复制代码这么做的原因是如果我们当前的路径下也有一个叫做math的Python文件，那么会覆盖系统自带的math的模块 。这是尤其需要注意的，不小心会导致很多奇怪的bug 。
类我们来看一个完整的类，相关的介绍都在注释当中
# We use the "class" statement to create a classclass Human:# A class attribute. It is shared by all instances of this class# 类属性，可以直接通过Human.species调用，而不需要通过实例species = "H. sapiens"# Basic initializer, this is called when this class is instantiated.# Note that the double leading and trailing underscores denote objects# or attributes that are used by Python but that live in user-controlled# namespaces. Methods(or objects or attributes) like: __init__, __str__,# __repr__ etc. are called special methods (or sometimes called dunder methods)# You should not invent such names on your own.# 最基础的构造函数# 加了下划线的函数和变量表示不应该被用户使用，其中双下划线的函数或者是变量将不会被子类覆盖# 前后都有双下划线的函数和属性是类当中的特殊属性def __init__(self, name):# Assign the argument to the instance's name attributeself.name = name# Initialize propertyself._age = 0# An instance method. All methods take "self" as the first argument# 类中的函数，所有实例可以调用，第一个参数必须是self# self表示实例的引用def say(self, msg):print("{name}: {message}".format(name=self.name, message=msg))# Another instance methoddef sing(self):return 'yo... yo... microphone check... one two... one two...'# A class method is shared among all instances# They are called with the calling class as the first argument@classmethod# 加上了注解，表示是类函数# 通过Human.get_species来调用，所有实例共享def get_species(cls):return cls.species# A static method is called without a class or instance reference@staticmethod# 静态函数，通过类名或者是实例都可以调用def grunt():return "*grunt*"# A property is just like a getter.# It turns the method age() into an read-only attribute of the same name.# There's no need to write trivial getters and setters in Python, though.@property# property注解，类似于get，set方法# 效率很低，除非必要，不要使用def age(self):return self._age# This allows the property to be set@age.setterdef age(self, age):self._age = age# This allows the property to be deleted@age.deleterdef age(self):del self._age以上内容的详细介绍之前也有过相关文章，可以查看：
Python——slots，property和对象命名规范
下面我们来看看Python当中类的使用：
# When a Python interpreter reads a source file it executes all its code.# This __name__ check makes sure this code block is only executed when this# module is the main program.# 这个是main函数也是整个程序入口的惯用写法if __name__ == '__main__':# Instantiate a class# 实例化一个类，获取类的对象i = Human(name="Ian")# 执行say方法i.say("hi")# "Ian: hi"j = Human("Joel")j.say("hello")# "Joel: hello"# i和j都是Human的实例，都称作是Human类的对象# i and j are instances of type Human, or in other words: they are Human objects# Call our class method# 类属性被所有实例共享，一旦修改全部生效i.say(i.get_species())# "Ian: H. sapiens"# Change the shared attributeHuman.species = "H. neanderthalensis"i.say(i.get_species())# => "Ian: H. neanderthalensis"j.say(j.get_species())# => "Joel: H. neanderthalensis"# 通过类名调用静态方法# Call the static methodprint(Human.grunt())# => "*grunt*"# Cannot call static method with instance of object# because i.grunt() will automatically put "self" (the object i) as an argument# 不能通过对象调用静态方法，因为对象会传入self实例，会导致不匹配print(i.grunt())# => TypeError: grunt() takes 0 positional arguments but 1 was given# Update the property for this instance# 实例级别的属性是独立的，各个对象各自拥有，修改不会影响其他对象内的值i.age = 42# Get the propertyi.say(i.age)# => "Ian: 42"j.say(j.age)# => "Joel: 0"# Delete the propertydel i.age# i.age# => this would raise an AttributeError 
这里解释一下，实例和对象可以理解成一个概念，实例的英文是instance，对象的英文是object 。都是指类经过实例化之后得到的对象 。


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