Understanding Python staticmethod and classmethod with Examples

In Python, the staticmethod decorator defines a method that does not receive an implicit first argument (neither self nor cls ), allowing it to be called on the class without instantiation.

class C(object):
    @staticmethod
    def f(arg1, arg2, ...):
        ...

The classmethod decorator creates a method that receives the class itself as the first argument ( cls ), enabling access to class attributes and other class methods without needing an instance.

# -*- coding: utf-8 -*-
class A(object):
    _g = 1
    def foo(self, x):
        print('executing foo(%s,%s)' % (self, x))
    @classmethod
    def class_foo(cls, x):
        print('executing class_foo(%s,%s)' % (cls, x))
    @staticmethod
    def static_foo(x):
        print('executing static_foo(%s)' % x)

a = A()
a.foo(1)
a.class_foo(1)
A.class_foo(1)
a.static_foo(1)
A.static_foo('hi')
print(a.foo)
print(a.class_foo)
print(a.static_foo)
# 输出：
# executing foo(<__main__.A object at 0x...>,1)
# executing class_foo(
,1)
# executing class_foo(
,1)
# executing static_foo(1)
# executing static_foo(hi)
#
>
#
>
#

A practical application is shown with a Date class that uses a class method to construct an instance from a string and a static method to validate date strings.

# -*- coding: utf-8 -*-
class Date(object):
    day = 0
    month = 0
    year = 0
    def __init__(self, day=0, month=0, year=0):
        self.day = day
        self.month = month
        self.year = year
    def display(self):
        return "{0}*{1}*{2}".format(self.day, self.month, self.year)
    @classmethod
    def from_string(cls, date_as_string):
        day, month, year = map(int, date_as_string.split('-'))
        date1 = cls(day, month, year)
        return date1
    @staticmethod
    def is_date_valid(date_as_string):
        day, month, year = map(int, date_as_string.split('-'))
        return day <= 31 and month <= 12 and year <= 3999

date1 = Date('12', '11', '2014')
date2 = Date.from_string('11-13-2014')
print(date1.display())
print(date2.display())
print(date2.is_date_valid('11-13-2014'))
print(Date.is_date_valid('11-13-2014'))
# 输出：
# 12*11*2014
# 11*13*2014
# False
# False

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