When in a Python interactive session:
In [1]: a = "my string"
In [2]: b = "my string"
In [3]: a == b
Out[3]: True
In [4]: a is b
Out[4]: False
In [5]: import sys
In [6]: print(sys.version)
3.5.2 (default, Nov 17 2016, 17:05:23)
[GCC 5.4.0 20160609]
On the other hand, when running the following program:
#!/usr/bin/env python
import sys
def test():
a = "my string"
b = "my string"
print(a == b)
print(a is b)
if __name__ == "__main__":
test()
print(sys.version)
The output is:
True
True
3.5.2 (default, Nov 17 2016, 17:05:23)
[GCC 5.4.0 20160609]
Why a is b has different outcome in the above two cases?
I am aware of this answer (and of course the difference between the == and is operators! that is the point of the question!) but aren't a and b the same object also in the first case? (interpeter?) since they point to the same (immutable) string?
This is caused by string interning. See this question for another example.
In your example, CPython interns the string constants in the module but doesn't in the REPL.