Question

I have some code of the form:

for i in range(nIterations):
    y = f(y)

Where f is a function defined elsewhere. hopefully the idea of that code is that after it’s run y will have had f applied to it nIterations times.

Is there a way in python to write this in a single line?

Answer 1

like this?

for i in range(nIterations): y = f(y)

A for loop with one command can be written as a single line.

EDIT

Or maybe slightly cleaner:

for _ in xrange(nIterations): y = f(y)

Since you don’t want to have a something that can be split into two separate statements (i think), here’s another one:

reduce(lambda y, _: f(y), xrange(nIterations), initValue)

Still, I would recommend to just use your original code, which is much more intuitive and readable. Also note what Guido van Rossum has to say on loops versus repeat.
Note by the way that (in python 2.x) xrange is more efficient than range for large nIterations as it returns an actual iterator and not an allocated list.