Python knows a number of compound data types, used to group together other values. The most versatile is the list, which can be written as a list of comma-separated values (items) between square brackets. List items need not all have the same type.
>>> a = ['foo', 'bar', 100, 1234] >>> a ['foo', 'bar', 100, 1234] >>>Like string indices, list indices start at 0, and lists can be sliced, concatenated and so on:
>>> a[0] 'foo' >>> a[3] 1234 >>> a[-2] 100 >>> a[1:-1] ['bar', 100] >>> a[:2] + ['bletch', 2*2] ['foo', 'bar', 'bletch', 4] >>> 3*a[:3] + ['Boe!'] ['foo', 'bar', 100, 'foo', 'bar', 100, 'foo', 'bar', 100, 'Boe!'] >>>Unlike strings, which are immutable, it is possible to change individual elements of a list:
>>> a ['foo', 'bar', 100, 1234] >>> a[2] = a[2] + 23 >>> a ['foo', 'bar', 123, 1234] >>>Assignment to slices is also possible, and this can even change the size of the list:
>>> # Replace some items: ... a[0:2] = [1, 12] >>> a [1, 12, 123, 1234] >>> # Remove some: ... a[0:2] = [] >>> a [123, 1234] >>> # Insert some: ... a[1:1] = ['bletch', 'xyzzy'] >>> a [123, 'bletch', 'xyzzy', 1234] >>> a[:0] = a # Insert (a copy of) itself at the beginning >>> a [123, 'bletch', 'xyzzy', 1234, 123, 'bletch', 'xyzzy', 1234] >>>The built-in function len() also applies to lists:
>>> len(a) 8 >>>It is possible to nest lists (create lists containing other lists), for example:
>>> q = [2, 3]
>>> p = [1, q, 4]
>>> len(p)
3
>>> p[1]
[2, 3]
>>> p[1][0]
2
>>> p[1].append('xtra') # See section 5.1
>>> p
[1, [2, 3, 'xtra'], 4]
>>> q
[2, 3, 'xtra']
>>>
Note that in the last example, p[1] and q really refer to
the same object! We'll come back to object semantics later.