Python Language List: Difference between revisions
Line 56: | Line 56: | ||
==Test for Existence of an Element in List== | ==Test for Existence of an Element in List== | ||
==Access an Element in List== | ==Access an Element in List== | ||
The element of a list can be accessed using the <code>[<I>offset</I>]</code> syntax. | The element of a list can be accessed using the <code>[<I><offset></I>]</code> syntax. The offset is zero-based. | ||
==<span id='Size of a List'></span>Length of a List== | ==<span id='Size of a List'></span>Length of a List== |
Revision as of 00:04, 7 March 2022
Internal
Overview
A list is a mutable sequence type that contains zero or more elements and whose elements can be of the same type or different types. The elements of a list are ordered. As mentioned, the list is mutable, in that a list can be changed in-place, new elements can be added to it, and existing elements can be overwritten. Unlike a set, a list can contain the same element multiple times, a list element does not need to be unique in the list.
List type()
The function type()
applied to a list returns:
<class 'list'>
To check whether an instance is a list:
i = ...
if type(i) is list:
...
For list
subclasses:
i = ...
if isinstance(i, list):
...
Create a List
A list can be created with the []
syntax, with the list()
functions and with list comprehensions.
Create a List with []
A list can be created specifying the list elements, separate them by comma and enclose them in square brackets.
empty_list = []
some_list = ['A', 'B', 'C']
some_other_list = ['A', 2, 3.0, ['B', 4]]
Create a List or Convert other Data Type to a List with list()
An empty list can be created with the list()
function:
empty_list = list()
The list()
function converts the data types to lists. The data types that can be converted are:
String to List
s = 'abc'
l = list(s) # l is ['a', 'b', 'c']
Tuple to List
t = ('a', 'b', 'c')
l = list(t) # l is ['a' ,'b', 'c']
Access a List
Test for Empty List
Test for Existence of an Element in List
Access an Element in List
The element of a list can be accessed using the [<offset>]
syntax. The offset is zero-based.
Length of a List
The number of elements is given by the len()
function:
l = [...]
print(len(l))
Iterate over a List
l = ['A', 'B', 'C']
for i, e in enumerate(l):
print(f'index: {i}, element: {e}')
Slices
Assign the sublist to l
:
l = l[:-1]
Modify a List
Modify Individual Elements
Append an Element
l.append(e)
Delete the Last Element
del l[-1]
Delete All Elements
List Processing
split(), join()
A string can be converted into a list containing tokens delimited by separators in the string using the split()
function. split()
is a string function. The elements of the newly created list are strings.
s='a b c'
l = s.split(' ') # l is ['a', 'b', 'c']
If two separators occur in succession in the string, the list contains an empty string:
s='a,,b,c'
l = s.split(',') # l is ['a', '', 'b', 'c']
Sorting
TO DEPLETE
Join the List Elements in a String
Join the elements of the given list in a string, using '-' as separator:
li = ['a', 'b']
s = '-'.join(li)
Only works if the list elements are strings.
Extract Elements from the Tail of the List Starting with a Certain Index
l = [1, 2, 3]
print(l[0:]) # prints [1, 2, 3]
print(l[1:]) # prints [2, 3]
print(l[2:]) # prints [3]
print(l[3:]) # prints [] (empty list)
print(l[4:]) # prints [] (empty list)
Extract Elements from the Head of the List Counting from the Tail
TODO