« Previous Next »

Python Lists

Lists are ordered, mutable (changeable) sequences of items. They can contain items of different data types.

1. Creating Lists:

Create lists using square brackets [], separating items by commas:

my_list = [] # Empty List
my_list = [1,2,3] # list of integers
my_list = [1, "hello", 3.14] #List with mixed data types

2. Accessing list items

You can access individual list elements by their index just like strings

my_list = [1,2,3,"Python",5.4,[5,6]]
print(my_list[0]) #Accesses the first element which is at index 0 so prints :1
print(my_list[3]) # Accesses the element at index 3 : "Python"
print(my_list[-1]) # List also support the negative indexing it print [5,6]
print(my_list[0:4]) #prints items form 0 index to 3 index [1, 2, 3, 'Python']

3. List Methods

Numerous methods available for List manipulation given use as one of more frequently seen in practice, these examples highlight main and common or helpful, practical ones of high utility in typical circumstances

Method Description Example
append() Adds a new element at the end my_list.append(6)
insert() Inserts element at a specific index my_list.insert(1,"SQL")
extend() Adds all the elements of an iterable (list, tuple, string etc.) to the end my_list.extend([7,8,9])
remove() Removes specified item. ValueError exception thrown if missing my_list.remove("SQL")
pop() Removes element at specified index removed_element = my_list.pop(2) #removes at index 2
del() Keyword. Like prior remove/pop it can be given some positional numeric indice to remove and from thereby in terms of its effects although implemented quite differently del my_list[0] # delete element at zeroth index
clear() Deletes all from list making empty my_list.clear()
sort() sorts ascending if no argument is given otherwise uses specified my_list = [3,1,4,1,5,9,2,6]
my_list.sort() sorts from lowest number upward like counting normally do, from small->large without need to change original, you sort rather than needing all other functions and loops and so on just to keep as originally organized for sake of not hardcoding initial element sequence rather than using indices later as could do given ordered unlike dict so remains correct regardless given sorting by method alone rather than original array contents themselves
reverse() Reverses element order my_list.reverse()
copy() Creates/returns list copy my_list2 = my_list.copy() # new_list variable you retain and do not lose initial for later even if same contents held
count() counts num occurrences, specific val if that desired, you count everything inside list itself cnt = my_list.count(1) # now cnt = 2 since we're seeing it twice within that initial list itself, 1 appearing two times within that whole unordered array variable itself so check against specific items when creating logic given how this counting function intended as designed and thereby functions when using Python code
index() Gives position of specific value where if seen more than once in the data only returns its earliest matching numeric indice during a scan over values rather than multiple as would result otherwise pos= my_list.index(1)
# 1 at two positions - (1, 4)
# now pos = 1 since checking position of its earlier rather than latest match. you locate positions only as result even if elements are repeated unlike prior example counting every appearance
# list methods list_methods = [1,2,3,4,5]
list_methods.append(6) # append element at the last
print(list_methods) #[1, 2, 3, 4, 5, 6]
list_methods.insert(0,0) # 0 added at index 0 rest of list shifts to the right
print(list_methods) #[0, 1, 2, 3, 4, 5, 6]
list_methods.remove(2) #Remove the element '2'
print(list_methods) #[0, 1, 3, 4, 5, 6]
popped_element = list_methods.pop(1) #Remove the element from 1 index, and value popped from List gets returned by .pop() method
print("Removed element using pop:",popped_element ) # 1
print(list_methods) #[0, 3, 4, 5, 6]
del list_methods[0]
#delete element using del
print(list_methods) #[3, 4, 5, 6]
« Previous Next »