Python探索之静态方法和类方法的区别详解

面相对象程序设计中，类方法和静态方法是经常用到的两个术语。
逻辑上讲：类方法是只能由类名调用；静态方法可以由类名或对象名进行调用。

python staticmethod and classmethod

Though classmethod and staticmethod are quite similar, there's a slight difference in usage for both entities: classmethod must have a reference to a class object as the first parameter, whereas staticmethod can have no parameters at all.Let's look at all that was said in real examples.

尽管 classmethod 和 staticmethod 非常相似，但在用法上依然有一些明显的区别。classmethod 必须有一个指向 类对象 的引用作为第一个参数，而 staticmethod 可以没有任何参数。

让我们看几个例子。

例子 – Boilerplate

Let's assume an example of a class, dealing with date information (this is what will be our boilerplate to cook on):

class Date(object):   def __init__(self, day=0, month=0, year=0):    self.day = day    self.month = month    self.year = year

This class obviously could be used to store information about certain dates (without timezone information; let's assume all dates are presented in UTC).

很明显，这个类的对象可以存储日期信息（不包括时区，假设他们都存储在 UTC）。

Here we have __init__, a typical initializer of Python class instances, which receives arguments as a typical instancemethod, having the first non-optional argument (self) that holds reference to a newly created instance.

这里的 init 方法用于初始化对象的属性，它的第一个参数一定是 self，用于指向已经创建好的对象。

Class Method

We have some tasks that can be nicely done using classmethods.
Let's assume that we want to create a lot of Date class instances having date information coming from outer source encoded as a string of next format (‘dd-mm-yyyy'). We have to do that in different places of our source code in project.

利用 classmethod 可以做一些很棒的东西。

比如我们可以支持从特定格式的日期字符串来创建对象，它的格式是 (‘dd-mm-yyyy')。很明显，我们只能在其他地方而不是 init 方法里实现这个功能。

So what we must do here is:
Parse a string to receive day, month and year as three integer variables or a 3-item tuple consisting of that variable.
Instantiate Date by passing those values to initialization call.
This will look like:

大概步骤：

解析字符串，得到整数 day， month， year。

使用得到的信息初始化对象

代码如下

day, month, year = map(int, string_date.split('-'))date1 = Date(day, month, year)