在python中是否允许“key not In container”，或者我们必须写“not（key In container）”

在python中，我知道可以编写：

happy_bag = list()

if not (key in happy_bag):
    print(key, " ain't in da bag.")

happy_bag = list()

if key not in happy_bag:
    print(key, " ain't in da bag.")

container = []
key = 1
if key not in container:
    print("Not found")

但也可以写下：

happy_bag = list()

if not (key in happy_bag):
    print(key, " ain't in da bag.")

happy_bag = list()

if key not in happy_bag:
    print(key, " ain't in da bag.")

container = []
key = 1
if key not in container:
    print("Not found")

此外，以下内容是合法的：

if key in happy_bag:
    print("Congratulations! you have a ", key, " in your bag!")

但是如果我们加上“是”这个词可以吗

if key is in happy_bag:
    print("Congratulations! you have a ", key, " in your bag!")

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这样写是完全正确的：

happy_bag = list()

if not (key in happy_bag):
    print(key, " ain't in da bag.")

happy_bag = list()

if key not in happy_bag:
    print(key, " ain't in da bag.")

container = []
key = 1
if key not in container:
    print("Not found")

甚至有人建议这样做。从

使用非运算符而不是非运算符。。。是虽然两个表达式在功能上完全相同，但前者更具可读性且更可取

关于第二个问题，在python中不是正确的运算符。运算符用于测试参考标识：

a = []
b = []
c = a
assert(a == b) # good, the two lists compare equal as per list.__eq__
assert(a is b) # fails, the two names don't refer to the same object
assert(a is c) # good, c and a point to the same list

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如果只是有一些交互式Python解释器来检查一下-标题和内容不同步。你似乎已经回答了标题，但却提出了一个新问题。只是一个问题：如果可能的话，你会期望它做什么？@MSeifert我想他们正在努力让它更接近英语。他们可能不打算对实际的接线员采取行动。不，那是不可能的。你不可能总是让代码读得很好。