python - a 和 b 的任意值使得 (a in b and b in a)==True

Question

是否有关于此函数(在 python3 中)返回 True 的参数？

def p(a,b):
    return (a in b and b in a)

Answer 1

是的，一对相互包含的列表:

a, b = [], []
a.append(b)
b.append(a)
print(a in b and b in a)

或者，一个包含自身的列表:

a = b = []
a.append(a)
print(a in b and b in a)

或者，破解 __contains__，in 运算符调用:

class Foo:
    def __contains__(self, other):
        return True

a = Foo()
b = Foo()
print(a in b and b in a)

或者，相等的字符串:

a = 'foo'
b = 'foo'
print(a in b and b in a)

或者，相互产生的生成器:

def foo():
    x = yield
    while True:
        yield x

a = foo()
b = foo()
next(a)
next(b)
a.send(b)
b.send(a)
print(a in b and b in a)

这是个笑话，它永远不会结束:

import math
from itertools import count
a = math.inf
b = count()
print(a in b and b in a)