Python Lists
The list is a most flexible datatype available in Python which may be written as a listing of comma-separated values (objects) among rectangular brackets. Important component approximately a list is that gadgets in a list need not be of the identical kind. Creating a listing is as easy as placing specific comma-separated values among rectangular brackets. For instance −list1 = ['physics', 'chemistry', 1997, 2000];
list2 = [1, 2, 3, 4, 5 ];
list3 = ["a", "b", "c", "d"]Accessing Values in Lists
To get admission to values in lists, use the square brackets for slicing in conjunction with the index or indices to reap fee available at that index. For instance −#!/usr/bin/python
list1 = ['physics', 'chemistry', 1997, 2000];
list2 = [1, 2, 3, 4, 5, 6, 7 ];
print "list1[0]: ", list1[0]
print "list2[1:5]: ", list2[1:5]list1[0]: physics
list2[1:5]: [2, 3, 4, 5]Updating Lists
You can replace unmarried or multiple elements of lists by means of giving the slice at the left-hand aspect of the project operator, and you may upload to elements in a listing with the append() approach. For example −#!/usr/bin/python
list = ['physics', 'chemistry', 1997, 2000];
print "Value available at index 2 : "
print list[2]
list[2] = 2001;
print "New value available at index 2 : "
print list[2]Value available at index 2 :
1997
New value available at index 2 :
2001Delete List Elements
To eliminate a listing detail, you could use both the del statement in case you recognise precisely which detail(s) you are deleting or the get rid of() approach if you do now not realize. For instance −#!/usr/bin/python
list1 = ['physics', 'chemistry', 1997, 2000];
print list1
del list1[2];
print "After deleting value at index 2 : "
print list1['physics', 'chemistry', 1997, 2000]
After deleting value at index 2 :
['physics', 'chemistry', 2000]Python – Lists, Basic List Operations
Lists respond to the + and * operators similar to strings; they suggest concatenation and repetition here too, except that the result is a brand new list, now not a string. In fact, lists respond to all of the overall sequence operations we used on strings inside the previous chapter.| Python Expression | Results | Description |
|---|---|---|
| len([1, 2, 3]) | 3 | Length |
| [1, 2, 3] + [4, 5, 6] | [1, 2, 3, 4, 5, 6] | Concatenation |
| [‘Hi!’] * 4 | [‘Hi!’, ‘Hi!’, ‘Hi!’, ‘Hi!’] | Repetition |
| 3 in [1, 2, 3] | True | Membership |
| for x in [1, 2, 3]: print x, | 1 2 3 | Iteration |
Python – Lists, Indexing, Slicing, and Matrixes
Because lists are sequences, indexing and slicing work the identical way for lists as they do for strings. Assuming following enter −L = ['spam', 'Spam', 'SPAM!']| Python Expression | Results | Description |
|---|---|---|
| L[2] | SPAM! | Offsets start at zero |
| L[-2] | Spam | Negative: count from the right |
| L[1:] | [‘Spam’, ‘SPAM!’] | Slicing fetches sections |
Python – Lists, Built-in List Functions & Methods
Python includes the following list functions −| Sr.No. | Function with Description |
|---|---|
| 1 | cmp(list1, list2)Compares elements of both lists. |
| 2 | len(list)Gives the total length of the list. |
| 3 | max(list)Returns item from the list with max value. |
| 4 | min(list)Returns item from the list with min value. |
| 5 | list(seq)Converts a tuple into list. |
| Sr.No. | Methods with Description |
|---|---|
| 1 | list.append(obj)Appends object obj to list |
| 2 | list.count(obj)Returns count of how many times obj occurs in list |
| 3 | list.extend(seq)Appends the contents of seq to list |
| 4 | list.index(obj)Returns the lowest index in list that obj appears |
| 5 | list.insert(index, obj)Inserts object obj into list at offset index |
| 6 | list.pop(obj=list[-1])Removes and returns last object or obj from list |
| 7 | list.remove(obj)Removes object obj from list |
| 8 | list.reverse()Reverses objects of list in place |
| 9 | list.sort([func])Sorts objects of list, use compare func if given |