Question

I saw a one liner code that is claimed to remove duplicates from a sequence:

u = [x for x in seq if x not in locals()['_[1]']]

I tried that code in ipython (with Python 2.7), it gave KeyError: '_[1]'

Does ['_[1]'] mean something special in Python?

Answer 1

locals()['_[1]'] is a way to access a reference to list comprehension (or generator) current result inside that list comprehension.

It is quite an evil, but can produce funny results:

>> [list(locals()['_[1]']) for x in range(3)]
[[], [[]], [[], [[]]]]

See more details here: the-secret-name-of-list-comprehensions.