What is list data structure in Python
Get to know list data structure
List is a sequence of data and list is a structure which can be changed.
Tuple is a sequence of data and cannot be change.
Lists are useful when you want to work with a collection of values. The items of a list are separated by commas and enclosed in square brackets.
A list can contain other lists. An empty list is simply written as two brackets, [].
None is a Python value and means nothing.
To initialize a list of length 10, you could do the following:
sequence = [None] * 10
print sequence
The code above generates the following result.
| Method | Description |
|---|---|
| list.append(object) | Add to the end of a list. |
| list.count(object) | Returns the number of i's for which list[i] == object. |
| list.extend(sequence) | Equivalent to list[len(list):len(list)] = sequence. |
| list.index(object) | Returns the smallest i for which list[i] == object (or raises a ValueError if no such i exists). |
| list.insert(index, object) | Equivalent to list[index:index] = [object] if index >= 0; if index < 0, object is prepended to the list. |
| list.pop([index]) | Removes and returns the item with the given index (default -1). |
| list.remove(object) | Equivalent to del list[list.index(object)]. |
| list.reverse() | Reverses the items of list in place. |
| list.sort([cmp][, key][, reverse]) | Sorts the items of list in place (stable sorting). Can be customized by supplying a comparison function, cmp; a key function, key, which will create the keys for the sorting); and a reverse flag (a Boolean value). |
Nested List
The following code creates a list q first and then use
q as one element to create
p. Now List p is a nested listed.
q = [2, 3]# from w ww.jav a2 s. co m
p = [1, q, 4]
print len(p)
print p[1]
print p[1][0]
p[1].append('xtra')
print p
print q
matrix = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
print matrix[1]
print matrix[1][1]
print matrix[2][0]
The code above generates the following result.
List for iteration
for x in [1, 2, 3]: print x, # iteration
The code above generates the following result.
For Statements
a = ['cat', 'window', 'defenestrate']
for x in a:
print x, len(x)
The code above generates the following result.
Loop through a list: for in
a = ['cat', 'window', 'defenestrate']
# w w w . ja v a 2s. c om
for x in a[:]: # make a slice copy of the entire list
if len(x) > 6: a.insert(0, x)
print a
The code above generates the following result.
To iterate over the indices of a sequence,
combine range() and len().
a = ['Mary', 'had', 'a', 'little', 'lamb']
for i in range(len(a)):
print i, a[i]
The code above generates the following result.
