python中变量

一、python中变量划分：

1、全局变量： 在模块内，所有class和def方法中。
2、局部变量：在模块内，在def方法内；
3、静态变量：在模块内，class内，但不在def方法中；
4、实例变量：在模块内，在class和def方法中，使用self修饰。

二、实例分析

# --*-- coding: utf8 --*--

# 全局变量
name = 'Lily'
job = 'dancer'
gender = 'male'

class people:
    # 静态变量
    city = "shenzhen"

    def __init__(self):
        # 实例变量，仅供当前类实例调用
        self.age = 12

    def changejob(self, jobb, nameb):
        # 方法内修改全局变量
        global job, name
        job =  jobb
        name = nameb

    def showinfo(self):
        # gender 为局部变量，仅供当前方法使用
        gender = 'Female'
        print("%s is a %s. She is %d years old. She is a %s, she is in %s " % (name, gender,self.age, job, self.city))


if __name__ == "__main__":
    p1 = people()
    p1.showinfo()
    people().changejob("singer", "Lucy")
    p2 = people()
    p2.showinfo()

Execute Result:

Lily is a Female. She is 12 years old. She is a dancer, she is in shenzhen 
Lucy is a Female. She is 12 years old. She is a singer, she is in shenzhen

解析：

全局变量，在模块内可以直接被调用，不需要添加任何前缀；
局部变量，在方法showinfo中，gender为局部变量，优先级高于全局变量，so执行结果为Female；
实例变量，在__init__方法中，定义的实例变量，仅供当前类的这个实例使用(如果其他类继承该类，并调用该构造方法，也可以使用)，使用时需要使用前缀self(self代表类的实例)；
静态变量：在class内，方法外的city是实例变量，使用时需要self前缀。

实例变量，在类继承中使用：

class people:
    def __init__(self,age=12, name='Tom', weight=None):
        self.age = age
        self.name = name
        self.weight = weight

    def speak(self):
        print("%s 说: 我 %d 岁" % (self.name, self.age))


class student(people):

    def __init__(self, age, name,job):
        # 如下2种方式，都可以调用父类的构造方法
        super().__init__(age, name)
        #people.__init__(self, age, name, weight=None)
        self.job = job

    def speak(self):
        print(self.age, self.name)
        print("% is a %s, she is %d" % (self.name, self.job, self.age))


if __name__ == "__main__":
    s = student(22, 'Lily','dancer')
    s.speak()

Execute Result:

Lily is a dancer, she is 22

在使用unittest测试框架中，发现一个问题：

import unittest

class people(unittest.TestCase):

    def setUp(self):
        pass

    def tearDown(self):
        pass

    def test_01_info(self):
        self.age = 22
        self.job = 'dancer'
        people.name = "Lily"
        people.test_01_list = dir(self)

    def test_02_speak(self):
        people.test_02_list = dir(self)
        print("%s is a %s, she is %d" % (self.name, self.job, self.age))

    def test_03_speak(self):
        print(self.test_01_list)
        print(self.test_02_list)
        print( list(set(self.test_01_list).difference(set(self.test_02_list))))

if __name__ == "__main__":
    unittest.main(verbosity=2)

Execute Result:

test_01_info (__main__.people) ... ok
test_02_speak (__main__.people) ... ERROR
test_03_speak (__main__.people) ... ok

======================================================================
ERROR: test_02_speak (__main__.people)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "D:/Richard/python/learn/Sock/test1.py", line 20, in test_02_speak
    print("%s is a %s, she is %d" % (self.name, self.job, self.age))
AttributeError: 'people' object has no attribute 'job'

----------------------------------------------------------------------
Ran 3 tests in 0.001s

FAILED (errors=1)
['__call__', ... , name, age, job]
['__call__', ... , name]
['job', 'age']

解析(暂时猜测，还不能肯定是正确的)：

在class的def方法内，self.age定义了实例1的实例属性，在test_01_info(self)方法完成后，该实例释放，实例相关属性释放，在test_02_speak(self)中，新创建的实例使用self.age时，会报错，提示：类没有age这个属性。
在在class的def方法内，people.name直接修改类非类某个实例的属性，people类实例都可以调用。

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