【易混淆】1-is 和 == , is not 与 !=

is 判断两个变量是否引用同一个对象，类比java的equal(); == 判断对象的内容是否相同，类比java的==
is not判断两个变量引用自不同的对象，而 != 判断两个变量的值不同

id() 可以查看变量（或者叫对象）的内存地址，可以分析两个变量分别引用哪一个对象

import time
def log(*args, **kwargs):
    print(*args, **kwargs)

# 测试id()
def test_3():
    log(id(1))
    log(id("abc"))
    log(id([1, 2, 3]))

# 测试整数
def test_4():
    x = 5000000 # 大整数
    y = 5000000
    log(x == y)
    log(x is y)
    log(id(x))
    log(id(y))


# 测试字符串
def test_5():
    x = "abc"
    y = "abc"
    log(x == y)
    log(x is y)
    log(id(x))
    log(id(y))


# 测试list
def test_6():
    x = [1, 2, 3]
    y = [1, 2, 3]
    log(x == y)
    log(x is y)
    log(id(x))
    log(id(y))


# 测试tuple
def test_7():
    x = (1, 2, 3)
    y = (1, 2, 3)
    log(x == y)
    log(x is y)
    log(id(x))
    log(id(y))

# 测试 dict
def test_8():
    x = {"id": 1, "name": "Tom", "age": 18}
    y = {"id": 1, "name": "Tom", "age": 18}
    log(x == y)
    log(x is y)
    log(id(x))
    log(id(y))


# 测试set
def test_9():
    x = set([1, 2, 3])
    y = set([1, 2, 3])
    log(x == y)
    log(x is y)
    log(id(x))
    log(id(y))


def test_10():
    x = [1, 2, 3]
    y = x # 说明这里是深拷贝，y和x都指向同一个对象
    log(x == y)
    log(x is y)
    log(id(x))
    log(id(y))

if __name__ == '__main__':
    # test_4()
    # test_5()
    # test_6()
    # test_7()
    # test_8()
    # test_9()
    test_10()

结论：

• 整数，字符串这些基础类型都是单例，值相同即引用的对象也相同
• list, tuple, dict, set这些集合即使值相同，但引用的对象都不同
• = 赋值的效果是，直接让两个变量指向同一个内存地址，即引用同一个对象