Data Structures

Lists

An example:

list = [1, 2, 3, -4.3, "blah", ['a', 'b', 'c']]
	

Many operations can be performed on lists:

• insert(i, x) will insert x into the list at position i.
• append(x) appends x to the list.
• index(x) returns the index of x in the list.
• remove(x) removes the first occurrence of x from the list.
• sort() sorts the list in place.
• reverse() reverses the list in place.
• count(x) returns the number of times x appears in the list.

Some operations have a nicer syntax than the above, for example:

list.append('a')
	

is equivalent to:

list + ['a']
	

Tuples

An example:

tuple = (x, y)
	

Tuples are like lists, except that once an instance has been created, it cannot be changed. The most common use of tuples is in making functions return more than one value:

return (a, b)
	

In fact, there is a short hand for tuples that makes this look even better:

return a, b
	

Neat, huh?

Dictionaries

This is simply another name for a hash table, it provides a mapping between keys and objects with a constant time look up of keys in the table. An example:

dict = {'feffi': 'feffi@hotmail.com', 'munchkin': 'munchkin@humbug.org'}
dict['feffi']
	

outputs:

'feffi@hotmail.com'
	

There are a few operations defined for dictionaries:

• keys() returns an unsorted list of all the keys in the dictionary.
• has_key(x) checks to see if the key x is in the dictionary.

Now to show how to pass arbitrary arguments to a function. If a function is defined thus:

def function(args**):
     print args

and call it like this:

function(foo='bar', bar='baz')
	

then it will output:

{'foo': 'bar', 'bar': 'baz'}