A Python list may hold different types of values.<\/p>\n
>>> days=['Monday','Tuesday','Wednesday',4,5,6,7.0]<\/pre>\nA list may have python list.<\/p>\n
>>> languages=[['English'],['Gujarati'],['Hindi'],'Romanian','Spanish']\r\n>>> languages<\/pre>\nOutput<\/strong><\/p>\n
[[‘English’], [‘Gujarati’], [‘Hindi’], ‘Romanian’, ‘Spanish’]<\/div>\n>>> type(languages[0])<\/pre>\nOutput<\/strong><\/p>\n
<class ‘list’><\/div>\nA list may also contain tuples or so.<\/p>\n
>>> languages=[('English','Albanian'),'Gujarati','Hindi','Romanian','Spanish']\r\n>>> languages[0]<\/pre>\nOutput<\/strong><\/p>\n
(‘English’, ‘Romanian’)<\/div>\n>>> type(languages[0])<\/pre>\nOutput<\/strong><\/p>\n
<class ‘tuple’><\/div>\n>>> languages[0][0]='Albanian'<\/pre>\nOutput<\/strong><\/p>\n
\nTraceback (most recent call last):File “<pyshell#24>”, line 1, in <module><\/p>\n
languages[0][0]=’Albanian’<\/p>\n
TypeError: ‘tuple’ object does not support item assignment<\/p>\n<\/div>\n
2. How to Access a List in Python?<\/h4>\n
To access a Python list as a whole, all you need is its name.<\/p>\n
>>> days<\/pre>\nOutput<\/strong><\/p>\n
\n[‘Monday’, ‘Tuesday’, ‘Wednesday’, 4, 5, 6, 7.0]<\/p>\n<\/div>\n
Or, you can put it in a print statement.<\/p>\n
>>> languages=[['English'],['Gujarati'],['Hindi'],'Romanian','Spanish']\r\n>>> print(languages)<\/pre>\nOutput<\/strong><\/p>\n
[[‘English’], [‘Gujarati’], [‘Hindi’], ‘Romanian’, ‘Spanish’]<\/div>\nTo access a single element, use its index in square brackets after the list\u2019s name. Indexing begins at 0.<\/p>\n
>>> languages[0]<\/pre>\nOutput<\/strong><\/p>\n
[‘English’]<\/div>\nAn index cannot be a float value.<\/p>\n
>>> languages[1.0]<\/pre>\nOutput<\/strong><\/p>\n
\nTraceback (most recent call last):File “<pyshell#70>”, line 1, in <module><\/p>\n
languages[1.0]<\/p>\n
TypeError: list indices must be integers or slices, not float<\/p>\n<\/div>\n
3. Slicing a Python List<\/h4>\n
When you want only a part of a Python list, you can use the slicing operator [].<\/p>\n
>>> indices=['zero','one','two','three','four','five']\r\n>>> indices[2:4]<\/pre>\nOutput<\/strong><\/p>\n
[‘two’, ‘three’]<\/div>\nThis returns items from index 2 to index 4-1 (i.e., 3)<\/p>\n
>>> indices[:4]<\/pre>\nOutput<\/strong><\/p>\n
[‘zero’, ‘one’, ‘two’, ‘three’]<\/div>\nThis returns items from the beginning of the list to index 3.<\/p>\n
>>> indices[4:]<\/pre>\nOutput<\/strong><\/p>\n
[‘four’, ‘five’]<\/div>\nIt returns items from index 4 to the end of the list in Python.<\/p>\n
>>> indices[:]<\/pre>\nOutput<\/strong><\/p>\n
[‘zero’, ‘one’, ‘two’, ‘three’, ‘four’, ‘five’]<\/div>\nThis returns the whole list.<\/p>\n
\n
- Negative indices- <\/strong>The indices we mention can be negative as well. A negative index means traversal from the end of the list.<\/li>\n<\/ul>\n
>>> indices[:-2]<\/pre>\nOutput<\/strong><\/p>\n
[‘zero’, ‘one’, ‘two’, ‘three’]<\/div>\nThis returns item from the list\u2019s beginning to two items from the end.<\/p>\n
>>> indices[1:-2]<\/pre>\nOutput<\/strong><\/p>\n
[‘one’, ‘two’, ‘three’]<\/div>\nIt returns items from the item at index 1 to two items from the end.<\/p>\n
>>> indices[-2:-1]<\/pre>\nOutput<\/strong><\/p>\n
[‘four’]<\/div>\nThis returns items from two from the end to one from the end.<\/p>\n
>>> indices[-1:-2]<\/pre>\nOutput<\/strong><\/p>\n
[]<\/div>\nThis returns an empty Python\u00a0list, because the start is ahead of the stop for the traversal.<\/p>\n
4. Reassigning a Python List (Mutable)<\/h4>\n
Python Lists are mutable. This means that you can reassign its items, or you can reassign it as a whole. Let\u2019s take a new list.<\/p>\n
>>> colors=['red','green','blue']<\/pre>\na. Reassigning the whole Python list<\/h4>\n
You can reassign a Python list by assigning it like a new list.<\/p>\n
>>> colors=['caramel','gold','silver','occur']\r\n>>> colors<\/pre>\nOutput<\/strong><\/p>\n
[‘caramel’, ‘gold’, ‘silver’, ‘occur’]<\/div>\nb. Reassigning a few elements<\/h4>\n
You can also reassign a slice of a list in Python.<\/p>\n
>>> colors[2:]=['bronze','silver']\r\n>>> colors<\/pre>\nOutput<\/strong><\/p>\n
[‘caramel’, ‘gold’, ‘bronze’, ‘silver’]<\/div>\nIf we had instead put two values to a single one in the left, see what would\u2019ve happened.<\/p>\n
>>> colors=['caramel','gold','silver','occur']\r\n>>> colors[2:3]=['bronze','silver']\r\n>>> colors<\/pre>\nOutput<\/strong><\/p>\n
[‘caramel’, ‘gold’, ‘bronze’, ‘silver’, ‘occur’]<\/div>\ncolors[2:3] reassigns the element at index 2, which is the third element.<\/p>\n
2:2 works too.<\/p>\n
>>> colors[2:2]=['occur']\r\n>>> colors<\/pre>\nOutput<\/strong><\/p>\n
[‘caramel’, ‘gold’, ‘occur’, ‘bronze’, ‘silver’]<\/div>\nc. Reassigning a single element in a List<\/h4>\n
You can reassign individual elements too.<\/p>\n
>>> colors=['caramel','gold','silver','occur']\r\n>>> colors[3]='bronze'\r\n>>> colors<\/pre>\nOutput<\/strong><\/p>\n
[‘caramel’, ‘gold’, ‘silver’, ‘bronze’]<\/div>\nNow, if you want to add another item, \u2018holographic\u2019, to the list, we cannot do it the conventional way.<\/p>\n
>>> colors[4]='holographic'<\/pre>\nOutput<\/strong><\/p>\n
\nTraceback (most recent call last):File “<pyshell#2>”, line 1, in <module><\/p>\n
colors[4]=’holographic’<\/p>\n
IndexError: list assignment index out of range<\/p>\n<\/div>\n
So, you need to reassign the whole list for the same.<\/p>\n
>>> colors=['caramel','gold','silver','bronze','holographic']\r\n>>> colors<\/pre>\nOutput<\/strong><\/p>\n
[‘caramel’, ‘gold’, ‘silver’, ‘bronze’, ‘holographic’]<\/div>\n3. How can we delete a Python List?<\/h4>\n
You can delete a Python list, some of its elements, or a single element.<\/p>\n
a. Deleting the entire Python list<\/h4>\n
Use the del keyword for the same.<\/p>\n
>>> del colors\r\n>>> colors<\/pre>\nOutput<\/strong><\/p>\n
\nTraceback (most recent call last):File “<pyshell#51>”, line 1, in <module><\/p>\n
colors<\/p>\n
NameError: name ‘colors’ is not defined<\/p>\n<\/div>\n
b. Deleting a few elements in the List<\/h4>\n
Use the slicing operator in Python to delete a slice.<\/p>\n
>>> colors=['caramel','gold','silver','bronze','holographic']\r\n>>> del colors[2:4]\r\n>>> colors<\/pre>\nOutput<\/strong><\/p>\n
[‘caramel’, ‘gold’, ‘holographic’]<\/div>\n>>> colors[2]<\/pre>\nOutput<\/strong><\/p>\n
‘holographic’<\/div>\nNow, \u2018holographic\u2019 is at position 2.<\/p>\n
c. Deleting a single element in a List<\/h4>\n
To delete a single element from a Python list, use its index.<\/p>\n
>>> del colors[0]\r\n>>> colors<\/pre>\nOutput<\/strong><\/p>\n
[‘gold’, ‘holographic’]<\/div>\nMultidimensional Lists in Python<\/h3>\n
Benefits of multidimensional Lists in Python:<\/strong><\/p>\n
\n
- Easy data organization:<\/strong> Data is being stored in rows and columns, which makes it easy to understand and work with spreadsheets and matrices.<\/li>\n
- Variety of data:<\/strong> These lists can store a variety of values like numbers, decimals, and texts.<\/li>\n
- No extra installations needed:<\/strong> Multidimensional lists come as a built- in feature in Python, so it doesn’t require any extra installation.<\/li>\n<\/ul>\n
You can also put a list in a list. Let\u2019s look at a multidimensional list.<\/p>\n
>>> grocery_list=[['caramel','P&B','Jelly'],['onions','potatoes'],['flour','oil']]\r\n>>> grocery_list<\/pre>\nOutput<\/strong><\/p>\n
[[‘caramel’, ‘P&B’, ‘Jelly’], [‘onions’, ‘potatoes’], [‘flour’, ‘oil’]]<\/div>\nThis is a grocery Python list with lists in it, where the lists are according to a category.<\/p>\n
Or, you can choose to go deeper.<\/p>\n
>>> a=[[[1,2],[3,4],5],[6,7]]\r\n>>> a<\/pre>\nOutput<\/strong><\/p>\n
[[[1, 2], [3, 4], 5], [6, 7]]<\/div>\nTo access element 4 here, we type the following code into the shell.<\/p>\n
>>> a[0][1][1]<\/pre>\nOutput<\/strong><\/p>\n
4<\/div>\nConcatenation of Python List<\/h3>\n
The concatenation operator works for lists as well. It lets us join two lists, with their orders preserved.<\/p>\n
>>> a,b=[3,1,2],[5,4,6]\r\n>>> a+b<\/pre>\nOutput<\/strong><\/p>\n
[3, 1, 2, 5, 4, 6]<\/div>\nPython List Operations<\/h3>\n
a. Multiplication Operation<\/h4>\n
This is an arithmetic operation. Multiplying a Python list by an integer makes copies of its items that a number of times while preserving the order.<\/p>\n
>>> a*=3\r\n>>> a<\/pre>\nOutput<\/strong><\/p>\n
[3, 1, 2, 3, 1, 2, 3, 1, 2]<\/div>\nHowever, you can\u2019t multiply it by a float.<\/p>\n
>>> a*3.0<\/pre>\nOutput<\/strong><\/p>\n
\nTraceback (most recent call last):File “<pyshell#89>”, line 1, in <module><\/p>\n
a*3.0<\/p>\n
TypeError: can’t multiply sequence by non-int of type ‘float’<\/p>\n<\/div>\n
b. Membership Operation<\/h4>\n
You can apply the \u2018in\u2019 and \u2018not in\u2019 operators on a Python list.<\/p>\n
>>> 1 in a<\/pre>\nOutput<\/strong><\/p>\n
True<\/div>\n>>> 2 not in a<\/pre>\nOutput<\/strong><\/p>\n
False<\/div>\nIterating on a list in Python<\/h3>\n
Python list can be traversed with a for loop\u00a0in python.<\/p>\n
>>> for i in [1,2,3]:\r\n if i%2==0:\r\n print(f\"{i} is composite\\n\")<\/pre>\nOutput<\/strong><\/p>\n
2 is composite<\/div>\nPython List Comprehension<\/h3>\n
You can create a new list just like you would in mathematics. To do so, type an expression followed by a for statement, all inside square brackets. You may assign it to a variable. Let\u2019s make a list for all even numbers from 1 to 20.<\/p>\n
>>> even=[2*i for i in range(1,11)]\r\n>>> even<\/pre>\nOutput<\/strong><\/p>\n
[2, 4, 6, 8, 10, 12, 14, 16, 18, 20]<\/div>\nOptionally, you can add an if-statement to filter out items. If we want to change this list to hold only those items from 1 to 20 that are even and are divisible by 3, we write the following code.<\/p>\n
>>> even=[2*i for i in range(1,11) if i%3==0]\r\n>>> even<\/pre>\n
![\"Python](\"https:\/\/data-flair.training\/blogs\/wp-content\/uploads\/sites\/2\/2017\/12\/Built-in-List-Functions-in-Python-01.jpg\")
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