_.startswith() overides the variable _

Question

Is the behaviour described below by purpose (Python 3.7) ?

_ = '==TEST=='
_.startswith('==')
Out[29]: True
_
Out[30]: True

l = '==TEST=='
l.startswith('==')
Out[26]: True
l
Out[27]: '==TEST=='

I know the variable names are a poor choice but why does the call to .startswith override the variable _ ?

Answer 1

When you run python in interactive mode it stores the value of each expression you evaluate into the underscore variable.