Mysterious for loop in python

Question

Let exp = [1,2,3,4,5]

If I then execute x in exp, it will give me False. But if I execute :

for x in exp:
             


        

Answer 1

Seems like you stumbled about in being somewhat overloaded in Python.

• with x in exp, you are asking "Is x in exp?"
• with for x in exp: ..., you tell Python "For each element in exp, call it x and do ..."

The latter will assign each of the values in exp to x, one after the other, and execute the body of the loop with that value, so in the first iteration x is assigned 1, in the second 2, and in the last 5. Also, x keeps this value after the loop!

Thus, before the loop, assuming that the variable x is defined but has some other value, x in exp will return False, and after the loop, it returns True, because x is still assigned the last value from exp.