l = range(100)
for i in l:
I've been bitten before by (someone else's) "clever" code that tries to modify a list while iterating over it. I resolved that I would never do it under any circumstance.
You can use the slice operator
mylist[::3] to skip across to every third item in your list.
mylist = [i for i in range(100)] for i in mylist[::3]: print(i),
Other points about my example relate to new syntax in python 3.0.
Python 3.0 range() now behaves like xrange() used to behave, except it works with values of arbitrary size. The latter no longer exists.