Use and meaning of "in" in an if statement?

Question

In an example from Zed Shaw's Learn Python the Hard Way, one of the exercises displays the following code:

next = raw_input("> ") if "0" in next or "1" in next:     how_much = int(next) 

I'm having a hard time understanding the meaning of in in this statement. I'm used to using if statements, such as in javascript, where the syntax is something like:

var = 5; if (var > 3) {     //code  to be executed } 

Is this if / in statement (in python) the same as if() in javascript?

Finding an answer to this has been tricky because the in is such a short string to narrow down an answer via search engine, and I don't know the proper name for its operation.

Answer 1

It depends on what next is.

If it's a string (as in your example), then in checks for substrings.

>>> "in" in "indigo" True >>> "in" in "violet" False >>> "0" in "10" True >>> "1" in "10" True 

If it's a different kind of iterable (list, tuple, set, dictionary...), then in checks for membership.

>>> "in" in ["in", "out"] True >>> "in" in ["indigo", "violet"] False 

In a dictionary, membership is seen as "being one of the keys":

>>> "in" in {"in": "out"} True >>> "in" in {"out": "in"} False 

Answer 2

Using a in b is simply translates to b.__contains__(a), which should return if b includes a or not.

But, your example looks a little weird, it takes an input from user and assigns its integer value to how_much variable if the input contains "0" or "1".