Modify a large list without any loops in python

Question

My list is:

a=[1,2,3,4]

Now I want my list to be:

a=[-1,-2,-3,-4]

How can I change my list this way without using any loops?

Update: this may be a large list, on the order of 10000 elements.

Answer 1

Use Python's map functionality

a[:] = map(lambda x: -x, a)

Here's the description of the map function from the above link:

map(function, iterable, ...)
Apply function to every item of iterable and return a list of the results. If additional iterable arguments are passed, function must take that many arguments and is applied to the items from all iterables in parallel. If one iterable is shorter than another it is assumed to be extended with None items. If function is None, the identity function is assumed; if there are multiple arguments, map() returns a list consisting of tuples containing the corresponding items from all iterables (a kind of transpose operation). The iterable arguments may be a sequence or any iterable object; the result is always a list.