Python Colon(:) in list index

Question

Hello All:

I'm new to Python. I see : used in list index especially when it's associated with functional calls, for e.g., python 2.7 document suggests that lists.append translates to a[len(a):] = [x]. Why do one have to suffix len(a) with a colon?

I understand that : is used to identify keys in dictionary. Thanks in advance for the help.

Answer 1

: is the delimiter of the slice syntax to 'slice out' sub-parts in sequences , [start:end]

[1:5] is equivalent to "from 1 to 5" (5 not included)
[1:] is equivalent to "1 to end"
[len(a):] is equivalent to "from length of a to end"

Watch http://www.youtube.com/watch?v=tKTZoB2Vjuk at around 40:00 he starts explaining that.

Works with tuples, dictionaries and lists, too.

Answer 2

slicing operator. http://docs.python.org/tutorial/introduction.html#strings and scroll down a bit