when __str__ and __repr__ are called in python code example

Example 1: __repr__ or __str__

very briefly
 - The default implementation is useless (it’s hard to think of one which wouldn’t be, but yeah)
 - __repr__ goal is to be unambiguous
 - __str__ goal is to be readable
 - Container’s __str__ uses contained objects’ __repr__
 
see source for more info

Example 2: python __repr__ meaning

>>>repr(y)
"'a string'"
>>>y2=eval(repr(y))
>>>y==y2
True