Colon (:) in Python list index [duplicate]

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I’m new to Python. I see : used in list indices especially when it’s associated with function calls.

Python 2.7 documentation suggests that lists.append translates to a[len(a):] = [x]. Why does one need to suffix len(a) with a colon?

I understand that : is used to identify keys in dictionary.

: 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 at around 40:00 he starts explaining that.

Works with tuples and strings, too.

slicing operator. and scroll down a bit

a[len(a):] – This gets you the length of a to the end. It selects a range. If you reverse a[:len(a)] it will get you the beginning to whatever is len(a).

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