list of user's variables in the interpreter

[Gribouillis]

If you only want the names in the main namespace you can use

# file ud.py
def u():
    import __main__
    return [w for w in dir(__main__) if w.strip('__') == w]

Then

>>> spam = 'eggs'
>>> ham = 3
>>> import ud
>>> ud.u()
['ham', 'spam', 'ud']