Python 相等判断

注：本篇完成时使用的Python版本为3.13.0

Python中，判断两变量是否相同，通常有is（is not）和 ==（!=）两种方法。

1、is / is not 身份运算符

用于比较两个对象的存储单元，即判断两个对象标识符是否引用自同一对象。

示例1： 

a = [1, 2, 3]
b = a
c = [1, 2, 3]
d = a.copy()
e = a[:]
print(f"a and b: {b is a}")
print(f"a and c: {c is a}")
print(f"a and d: {d is a}")
print(f"a and e: {e is a}")

结果为：

a and b: True
a and c: False
a and d: False
a and e: False

 示例2：

a = 10
b = a
c = 10
d = 10.0
print(f"a and b: {b is a}")
print(f"a and c: {c is a}")
print(f"a and d: {d is a}")
e = 2 ** 60
f = 2 ** 60
print(f"e and f: {f is e}")
g = 2 ** 80
h = 2 ** 80
print(f"g and h: {h is g}")
i = -100
j = -100
print(f"i and j: {j is i}")
k = 10.0
print(f"d and k: {k is d}")
l = "hello"
m = "hello"
print(f"l and m: {m is l}")

结果为：

a and b: True
a and c: True
a and d: False
e and f: True
g and h: False
i and j: True

d and k: True

l and m: True

可以发现，python3.13中，会预先创建部分int型、float型变量和简单字符串，当程序中使用的变量值在上述范围内时，均为对预创建变量的引用。

2、== / !=  比较运算符

用于比较两对象的值，判断其是否相等。

示例1：

a = [1, 2, 3]
b = a
c = [1, 2, 3]
d = a.copy()
e = a[:]
f = a[:2]
g = a[1:]
print(f"a and b: {b == a}")
print(f"a and c: {c == a}")
print(f"a and d: {d == a}")
print(f"a and e: {e == a}")
print(f"a and f: {f == a}")
print(f"a and g: {g == a}")

结果为：

a and b: True
a and c: True
a and d: True
a and e: True
a and f: False
a and g: False

示例2：

a = 10
b = a
c = 10
d = 10.0
print(f"a and b: {b == a}")
print(f"a and c: {c == a}")
print(f"a and d: {d == a}")

结果为：

a and b: True
a and c: True
a and d: True