Remove Specified Item
The remove() method removes the specified item.
Example
Remove "banana":
thislist = ["apple", "banana", "cherry"]
thislist.remove("banana")
print(thislist)Remove Specified Index
The pop() method removes the specified index.
Example
Remove the second item:
thislist = ["apple", "banana", "cherry"]
thislist.pop(1)
print(thislist)If you do not specify the index, the pop() method removes the last item.
Example
Remove the last item:
thislist = ["apple", "banana", "cherry"]
thislist.pop()
print(thislist)The del keyword also removes the specified index:
Example
Remove the first item:
thislist = ["apple", "banana", "cherry"]
del thislist[0]
print(thislist)The del keyword can also delete the list completely.
Example
Delete the entire list:
thislist = ["apple", "banana", "cherry"]
del thislistClear the List
The clear() method empties the list.
The list still remains, but it has no content.
Example
Clear the list content:
thislist = ["apple", "banana", "cherry"]
thislist.clear()
print(thislist)Loop Through a List
You can loop through the list items by using a for loop:
Example
Print all items in the list, one by one:
thislist = ["apple", "banana", "cherry"]
for x in thislist:
print(x)Learn more about for loops in our Python For Loops Chapter.
Loop Through the Index Numbers
You can also loop through the list items by referring to their index number.
Use the range() and len() functions to create a suitable iterable.
Example
Print all items by referring to their index number:
thislist = ["apple", "banana", "cherry"]
for i in range(len(thislist)):
print(thislist[i])The iterable created in the example above is [0, 1, 2].
Using a While Loop
You can loop through the list items by using a while loop.
Use the len() function to determine the length of the list, then start at 0 and loop your way through the list items by refering to their indexes.
Remember to increase the index by 1 after each iteration.
Example
Print all items, using a while loop to go through all the index numbers
thislist = ["apple", "banana", "cherry"]
i = 0
while i < len(thislist):
print(thislist[i])
i = i + 1Learn more about while loops in our Python While Loops Chapter.
Looping Using List Comprehension
List Comprehension offers the shortest syntax for looping through lists:
Example
A short hand for loop that will print all items in a list:
thislist = ["apple", "banana", "cherry"]
[print(x) for x in thislist]Python - List Comprehension
List comprehension offers a shorter syntax when you want to create a new list based on the values of an existing list.
Example:
Based on a list of fruits, you want a new list, containing only the fruits with the letter "a" in the name.
Without list comprehension you will have to write a for statement with a conditional test inside:
Example
fruits = ["apple", "banana", "cherry", "kiwi", "mango"]
newlist = []
for x in fruits:
if "a" in x:
newlist.append(x)
print(newlist)With list comprehension you can do all that with only one line of code:
Example
fruits = ["apple", "banana", "cherry", "kiwi", "mango"]
newlist = [x for x in fruits if "a" in x]
print(newlist)The Syntax
newlist = [expression for item in iterable if condition == True]The return value is a new list, leaving the old list unchanged.
Condition
The condition is like a filter that only accepts the items that valuate to True.
Example
Only accept items that are not "apple":
newlist = [x for x in fruits if x != "apple"]The condition if x != "apple" will return True for all elements other than "apple", making the new list contain all fruits except "apple".
The condition is optional and can be omitted:
Example
With no if statement:
newlist = [x for x in fruits]Iterable
The iterable can be any iterable object, like a list, tuple, set etc.
Example
You can use the range() function to create an iterable:
newlist = [x for x in range(10)]Same example, but with a condition:
Example
Accept only numbers lower than 5:
newlist = [x for x in range(10) if x < 5]Expression
The expression is the current item in the iteration, but it is also the outcome, which you can manipulate before it ends up like a list item in the new list:
Example
Set the values in the new list to upper case:
newlist = [x.upper() for x in fruits]You can set the outcome to whatever you like:
Example
Set all values in the new list to 'hello':
newlist = ['hello' for x in fruits]The expression can also contain conditions, not like a filter, but as a way to manipulate the outcome:
Example
Return "orange" instead of "banana":
newlist = [x if x != "banana" else "orange" for x in fruits]List objects have a sort() method that will sort the list alphanumerically, ascending, by default:
Example
Sort the list alphabetically:
thislist = ["orange", "mango", "kiwi", "pineapple", "banana"]
thislist.sort()
print(thislist)Example
Sort the list numerically:
thislist = [100, 50, 65, 82, 23]
thislist.sort()
print(thislist)Sort Descending
To sort descending, use the keyword argument reverse = True:
Example
Sort the list descending:
thislist = ["orange", "mango", "kiwi", "pineapple", "banana"]
thislist.sort(reverse = True)
print(thislist)Example
Sort the list descending:
thislist = [100, 50, 65, 82, 23]
thislist.sort(reverse = True)
print(thislist)Customize Sort Function
You can also customize your own function by using the keyword argument key = function.
The function will return a number that will be used to sort the list (the lowest number first):
Example
Sort the list based on how close the number is to 50:
def myfunc(n):
return abs(n - 50)
thislist = [100, 50, 65, 82, 23]
thislist.sort(key = myfunc)
print(thislist)Case Insensitive Sort
By default the sort() method is case sensitive, resulting in all capital letters being sorted before lower case letters:
Example
Case sensitive sorting can give an unexpected result:
thislist = ["banana", "Orange", "Kiwi", "cherry"]
thislist.sort()
print(thislist)Luckily we can use built-in functions as key functions when sorting a list.
So if you want a case-insensitive sort function, use str.lower as a key function:
Example
Perform a case-insensitive sort of the list:
thislist = ["banana", "Orange", "Kiwi", "cherry"]
thislist.sort(key = str.lower)
print(thislist)Reverse Order
What if you want to reverse the order of a list, regardless of the alphabet?
The reverse() method reverses the current sorting order of the elements.
Example
Reverse the order of the list items:
thislist = ["banana", "Orange", "Kiwi", "cherry"]
thislist.reverse()
print(thislist)You cannot copy a list simply by typing list2 = list1, because: list2 will only be a reference to list1, and changes made in list1 will automatically also be made in list2.
There are ways to make a copy, one way is to use the built-in List method copy().
Example
Make a copy of a list with the copy() method:
thislist = ["apple", "banana", "cherry"]
mylist = thislist.copy()
print(mylist)Another way to make a copy is to use the built-in method list().
Example
Make a copy of a list with the list() method:
thislist = ["apple", "banana", "cherry"]
mylist = list(thislist)
print(mylist)
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