Python 101 (part 3): A Twist In The Tail - We Don't Need Another Hero

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Unlike strings, lists are "mutable", which means that the elementscontained within a list can be changed at will. For example, any listelement can be altered simply by assigning a new value to it via its index.

>>> superheroes
['Spiderman', 'Superman', 'Human Torch', 'Batman']
>>> superheroes[3] = "Captain America"
>>> superheroes
['Spiderman', 'Superman', 'Human Torch', 'Captain America']
>>>

You can alter more than one value at a time by using list slices.

>>> superheroes
['Spiderman', 'Superman', 'Human Torch', 'Captain America']
>>> superheroes[0:2] = ["Incredible Hulk", "Green Lantern"]
>>> superheroes
['Incredible Hulk', 'Green Lantern', 'Human Torch', 'Captain America']
>>>

The built-in append() method makes it easy to add items to a list,

>>> superheroes
['Incredible Hulk', 'Green Lantern', 'Human Torch', 'Captain America']
>>> superheroes.append("Spawn")
>>> superheroes
['Incredible Hulk', 'Green Lantern', 'Human Torch', 'Captain America',
'Spawn']
>>>

while the del() method makes it just as easy to remove them.

>>> superheroes
['Incredible Hulk', 'Green Lantern', 'Human Torch', 'Captain America',
'Spawn']
>>> del superheroes[4]
>>> superheroes
['Incredible Hulk', 'Green Lantern', 'Human Torch', 'Captain America']
>>> del superheroes[0:2]
>>> superheroes
['Human Torch', 'Captain America']
>>>

Note that there's also a remove() method, which allows you to remove anelement by value rather than index.

>>> superheroes
['Incredible Hulk', 'Green Lantern', 'Human Torch', 'Captain America']
>>> superheroes.remove("Green Lantern")
>>> superheroes.remove("Captain America")
>>> superheroes
['Incredible Hulk', 'Human Torch']
>>>

Finally, the sort() and reverse() methods allow you to rearrange thecontents of a list.

>>> oldFlames
['Jennifer', 'Susan', 'Tina', 'Bozo The Clown']
>>> oldFlames.sort()
>>> oldFlames
['Bozo The Clown', 'Jennifer', 'Susan', 'Tina']
>>> oldFlames.reverse()
>>> oldFlames
['Tina', 'Susan', 'Jennifer', 'Bozo The Clown']
>>>

A number of other list methods are also available - take a look at thePython Library Reference at http://www.python.org/doc/current/lib/lib.htmlfor more information and examples.

Let's move on to loops.

Next: Looping The Loop >>
 

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