About the Python pit, A is "//" statement after a = "//" is true?

    这两天踩了个坑，用写LCS的时候，发现

The program uses this notation, and then it has been a bug.
A little silent. The storage type of the constant and the storage type of the variable are separated.
is determines whether the address of the left and right operands is compared is equal. Returns true if it is the same object, or False if it is the same.

It is important to note that when a variable is judged to be equal to a constant, it may always be false if it is used.

But I met a hole

"+"is"+"

"\\"is"\\"

The bool value of the two subsequent statements is different ... The former is true, the latter is false ...

This may be related to the escape character.

About the Python pit, A is "//" statement after a = "//" is true?