Why does comparing strings using either '==' or 'is' sometimes produce a different result?

Question

I've got a Python program where two variables are set to the value `'public'`. In a conditional expression I have the comparison `var1 is var2` which fails, but if I change it to `var1 == var2` it returns `True`.Now if I open my Python interpreter and do the same "is" comparison, it succeeds. >>> s1 = 'public' >>> s2 = 'public' >>> s2 is s1 TrueWhat am I missing here?

Answer 1

In python 'is' compares the memory addresses to see if the values refer to the same object. Python tries to optimize memory usage and will often refer multiple variable names to the same location if they have the same value. This optimization can differ between execution of a script and use of the terminal. Because of this you should not use 'is' to compare the value of objects.

Whereas '==' compares the values in the objects. This is the operator to which you should default.