How to remove all characters after a specific character in python?

Assuming your separator is '...', but it can be any string.

text = 'some string... this part will be removed.'
head, sep, tail = text.partition('...')

>>> print head
some string

If the separator is not found, head will contain all of the original string.

The partition function was added in Python 2.5.

S.partition(sep) -> (head, sep, tail)

Searches for the separator sep in S, and returns the part before it, the separator itself, and the part after it. If the separator is not found, returns S and two empty strings.

Split on your separator at most once, and take the first piece:

sep = '...'
stripped = text.split(sep, 1)[0]

You didn't say what should happen if the separator isn't present. Both this and Alex's solution will return the entire string in that case.