Learn Python in One Day and Learn It Well (2015)
Appendix B: Working With Lists
=> marks the start of the output
append( )
Add item to the end of a list
[Example]
myList = [‘a’, ‘b’, ‘c’, ‘d’]
myList.append(‘e’)
print (myList)
=> [‘a’, ‘b’, ‘c’, ‘d’, ‘e’]
del
Remove items from a list
[Example]
myList = [‘a’, ‘b’, ‘c’, ‘d’, ‘e’, ‘f’, ‘g’, ‘h’, ‘i’, ‘j’, ‘k’, ‘l’]
#delete the third item (index = 2)
del myList[2]
print (myList)
=> [‘a’, ‘b’, ‘d’, ‘e’, ‘f’, ‘g’, ‘h’, ‘i’, ‘j’, ‘k’, ‘l’]
#delete items from index 1 to 5-1
del myList[1:5]
print (myList)
=> [‘a’, ‘g’, ‘h’, ‘i’, ‘j’, ‘k’, ‘l’]
#delete items from index 0 to 3-1
del myList [ :3]
print (myList)
=> [‘i’, ‘j’, ‘k’, ‘l’]
#delete items from index 2 to end
del myList [2:]
print (myList)
=> [‘i’, ‘j’]
extend( )
Combine two lists
[Example]
myList = [‘a’, ‘b’, ‘c’, ‘d’, ‘e’]
myList2 = [1, 2, 3, 4]
myList.extend(myList2)
print (myList)
=> [‘a’, ‘b’, ‘c’, ‘d’, ‘e’, 1, 2, 3, 4]
In
Check if an item is in a list
[Example]
myList = [‘a’, ‘b’, ‘c’, ‘d’]
‘c’ in myList
=> True
‘e’ in myList
=> False
insert( )
Add item to a list at a particular position
[Example]
myList = [‘a’, ‘b’, ‘c’, ‘d’, ‘e’]
myList.insert(1, ‘Hi’)
print (myList)
=> [‘a’, ‘Hi’, ‘b’, ‘c’, ‘d’, ‘e’]
len( )
Find the number of items in a list
[Example]
myList = [‘a’, ‘b’, ‘c’, ‘d’]
print (len(myList))
=> 4
pop( )
Get the value of an item and remove it from the list
Requires index of item as the parameter
[Example]
myList = [‘a’, ‘b’, ‘c’, ‘d’, ‘e’]
#remove the third item
member = myList.pop(2)
print (member)
=> c
print (myList)
=> [‘a’, ‘b’, ‘d’, ‘e’]
#remove the last item
member = myList.pop( )
print (member)
=> e
print (myList)
=> [‘a’, ‘b’, ‘d’]
remove( )
Remove an item from a list. Requires the value of the item as the parameter.
[Example]
myList = [‘a’, ‘b’, ‘c’, ‘d’, ‘e’]
#remove the item ‘c’
myList.remove(‘c’)
print (myList)
=> [‘a’, ‘b’, ‘d’, ‘e’]
reverse()
Reverse the items in a list
[Example]
myList = [1, 2, 3, 4]
myList.reverse()
print (myList)
=> [4, 3, 2, 1]
sort()
Sort a list alphabetically or numerically
[Example]
myList = [3, 0, -1, 4, 6]
myList.sort()
print(myList)
=> [-1, 0, 3, 4, 6]
sorted()
Return a new sorted list without sorting the original list.
Requires a list as the parameter
[Example]
myList = [3, 0, -1, 4, 6]
myList2 = sorted(myList)
#Original list is not sorted
print (myList)
=> [3, 0, -1, 4, 6]
#New list is sorted
print (myList2)
=> [-1, 0, 3, 4, 6]
Addition Operator: +
Concatenate List
[Example]
myList = [‘a’, ‘b’, ‘c’, ‘d’]
print (myList + [‘e’, ‘f’])
=> [‘a’, ‘b’, ‘c’, ‘d’, ‘e’, ‘f’]
print (myList)
=> [‘a’, ‘b’, ‘c’, ‘d’]
Multiplication Operator: *
Duplicate a list and concatenate it to the end of the list
[Example]
myList = [‘a’, ‘b’, ‘c’, ‘d’]
print (myList*3)
=> ['a', 'b', 'c', 'd', 'a', 'b', 'c', 'd', 'a', 'b', 'c', 'd']
print (myList)
=> [‘a’, ‘b’, ‘c’, ‘d’]
Note:
The + and * symbols do not modify the list. The list stays as [‘a’, ‘b’, ‘c’, ‘d’] in both cases.