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Lists are the most versatile of Python's compound data types. A list contains items separated by commas and enclosed within square brackets ([]). To some extent, lists are similar to arrays in C. One difference between them is that all the items belonging to a list can be of different data type.
The values stored in a list can be accessed using the slice operator ([ ] and [:]) with indexes starting at 0 in the beginning of the list and working their way to end -1. The plus (+) sign is the list concatenation operator, and the asterisk (*) is the repetition operator.

For example − 
list = [ 'abcd', 786 , 2.23, 'john', 70.2 ]
tinylist = [123, 'john']
 
print list # Prints complete list
print list[0] # Prints first element of the list
print list[1:3] # Prints elements starting from 2nd till 3rd
print list[2:] # Prints elements starting from 3rd element
print tinylist * 2 # Prints list two times
print list + tinylist # Prints concatenated lists
 
This produce the following result −
['abcd', 786, 2.23, 'john', 70.200000000000003]
abcd
[786, 2.23]
[2.23, 'john', 70.200000000000003]
[123, 'john', 123, 'john']
['abcd', 786, 2.23, 'john', 70.200000000000003, 123, 'john']

 

List

Description

[]

An empty list

[1,1,2,3,5,8]

A list of integers

[42, "What's the question?", 3.1415]

A list of mixed data types

["Stuttgart", "Freiburg", "München", "Nürnberg", "Würzburg", "Ulm","Friedrichshafen", Zürich", "Wien"]

A list of Strings

[["London","England", 7556900], ["Paris","France",2193031], ["Bern", "Switzerland", 123466]]

A nested list

["High up", ["further down", ["and down", ["deep down", "the answer", 42]]]]

A deeply nested list


 

Updating Lists

You can update single or multiple elements of lists by giving the slice on the left-hand side of the assignment operator, and you can add to elements in a list with the append() method. For example −
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]
When the above code is executed, it produces the following result −

Value available at index 2 :

1997

New value available at index 2 :

2001

 

 

Delete List Elements

To remove a list element, you can use either the del statement if you know exactly which element(s) you are deleting or the remove() method if you do not know. For example −
 
list1 = ['physics', 'chemistry', 1997, 2000];
print list1
del list1[2];
print "After deleting value at index 2 : "
print list1
 
When the above code is executed, it produces following result −
['physics', 'chemistry', 1997, 2000]
After deleting value at index 2 :
['physics', 'chemistry', 2000]

 

 

Basic List Operations

Lists respond to the + and * operators much like strings; they mean concatenation and repetition here too, except that the result is a new list, not a string.
In fact, lists respond to all of the general sequence operations we used on strings in the prior 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

 

 

Indexing, Slicing and Matrixes

Because lists are sequences, indexing and slicing work the same way for lists as they do for strings.
Assuming following input −
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

 


Built-in List Functions & Methods:

cmp(list1, list2)

Compares elements of both lists.

len(list)

Gives the total length of the list.

max(list)

Returns item from the list with max value.

min(list)

Returns item from the list with min value.

list(seq)

Converts a tuple into list.

 

list.append(obj)

Appends object obj to list

list.count(obj)

Returns count of how many times obj occurs in list

list.extend(seq)

Appends the contents of seq to list

list.index(obj)

Returns the lowest index in list that obj appears

list.insert(index, obj)

Inserts object obj into list at offset index

list.pop(obj=list[-1])

Removes and returns last object or obj from list

list.remove(obj)

Removes object obj from list

list.reverse()

Reverses objects of list in place

list.sort([func])

Sorts objects of list, use compare func if given

 

 
         
 
 
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