Python 101 (part 3): A Twist In The Tail - Here Comes A Hero (
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Thus far, the variables you've used contain only a single value - for
example,
Python 1.5.2 (#1, Aug 25 2000, 09:33:37) [GCC 2.96 20000731
(experimental)] on linux-i386
Copyright 1991-1995 Stichting Mathematisch Centrum, Amsterdam
>>> i=0
>>> alpha=63453473458348383L
>>> name="god"
>>>
For simple Python programs, this is usually more than enough. However, as
your Python programs grow in complexity, you're going to need more advanced
data structures to store and manipulate information. And that's exactly
where lists come in.
Unlike string and number objects, which typically hold a single value, a
list can best be thought of as a "container" variable, which can contain
one or more values. For example,
>>> superheroes = ["Spiderman", "Superman", "Human Torch", "Batman"]
>>>
Here, "superheroes" is a list containing the values "Spiderman",
"Superman", "Human Torch", and "Batman".
Lists are particularly useful for grouping related values together - names,
dates, phone numbers of ex-girlfriends et al. The various elements of the
list are accessed via an index number, with the first element starting at
zero. So, to access the element "Superman", you would use the notation
>>> superheroes[0]
'Spiderman'
>>>
while
>>> superheroes[3]
'Batman'
>>>
- essentially, the list name followed by the index number enclosed within
square braces. Geeks refer to this as "zero-based indexing".
Defining a list is simple - simply assign values (enclosed in square
braces) to a variable, as illustrated below:
>>> oldFlames = ["Jennifer", "Susan", "Tina", "Bozo The Clown"]
>>>
The rules for choosing a list name are the same as those for any
other Python variable - it must begin with a letter, and can optionally be
followed by more letters and numbers.
If you've worked with other programming languages, it should now be obvious
that lists in Python are the equivalent of arrays in Perl, PHP and C.
However, unlike these languages, Python does not restrict lists to elements
of a specific object type, and can mix strings, numbers and even other
lists within a single list "container".
>>> allMixedUp = ["ding dong", 23, "abracadabra", 26346.3, [4, "four"]]
>>> allMixedUp
['ding dong', 23, 'abracadabra', 26346.3, [4, 'four']]
>>> allMixedUp[0]
'ding dong'
>>> allMixedUp[4]
[4, 'four']
>>> allMixedUp[4][0]
4
>>> allMixedUp[4][1]
'four'
>>>
