Variable assigned to the last executed line? [closed]

Answer 1

Take a look here Reserved identifiers python.

The special identifier _ is used in the interactive interpreter to store the result of the last evaluation; it is stored in the builtin module.

This behavior can be found on haskell's interactive environment ghci also. Here instead of _ use it.

Prelude> 2+2
4
Prelude> it
4

Answer 2

Per What is the purpose of the single underscore "_" variable in Python?

There are three main uses for _. One is "real" (the usage you discovered), and the other two are conventions.

Interesting... I never knew!

Answer 3

This isn't a big secret (for example, you can find it mentioned in Code Like a Pythonista) but true, it's not well known. It could be useful when you're doing a lot of work at the command line.

Answer 4

It's useful when exploring in the interactive interpreter, when you forgot to assign a name to some returned object, you can grab a reference to it using x = _. Note that in ipython you also have __ for the second-to-last returned, and ___ is the third-to-last.