In Python, lists are:
- ordered
- indexed (indices start at 0)
- mutable
- heterogeneous (items in a list need not be of the same type)
- written as a list of comma-separated values between square brackets
listOfSubjects = ['physics', 'chemistry', "mathematics"] listOfIds = [0, 1, 2, 3, 4] miscList = [0, 'one', 2, 'three']
1. Access list items
To access values in lists, use the square brackets in slicing syntax or array index form to get a single item or range of items.
The index values passed can be positive or negative both. A negative index value means start counting from the end of the list.
list [m : n]
means sublist start at index m
(included) and end at index n
(not included).
- If
m
is not provided then its value is assumed to be zero. - If
n
is not provided then range is selected till last of list.
ids = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] print( ids[0] ) # 0 print( ids[1:5] ) # [1, 2, 3, 4] print( ids[ : 3] ) # [0, 1, 2] print( ids[7 : ] ) # [7, 8, 9] print( ids[-8:-5] ) # [2, 3, 4]
2. Modily list
To change a specific item in the list, refer to it using it’s index and assign a new value.
charList = ["a", "b", "c"] charList [2] = "d" print (charList) # ['a', 'b', 'd']
3. Iterate a list
We can loop through the list items by using a for loop
.
charList = ["a", "b", "c"] for x in charList: print(x) # a # b # c
4. Check if a item exists in the list
Use the 'in'
keyword to determine if a specified item is present in a list.
charList = ["a", "b", "c"] if "a" in charList: print("a is present") # a is present if "d" in charList: print("d is present") else: print("d is NOT present") # d is NOT present
5. Finding length of the list
Use the len()
function to find the length of a given list.
charList = ["a", "b", "c"] x = len (charList) print (x) # 3
6. Adding items
- To add an item to the end of the list, use the
append(item)
method. - To add an item at specific index position, use the
insert(index, item)
method. Ifindex
is greater than index length, item is added at the end of the list.
charList = ["a", "b", "c"] charList.append("d") charList.append("e") print (charList) # ['a', 'b', 'c', 'd', 'e'] charList.insert(5, "f") print (charList) # ['a', 'b', 'c', 'd', 'e', 'f'] charList.insert(10, "h") # No error print (charList) # ['a', 'b', 'c', 'd', 'e', 'f', 'h']
7. Removing items
To remove an item from the list, use one of the four ways i.e. remove()
, pop()
, clear()
or del
keyword.
7.1. remove()
It removes the specified item by it’s value.
charList = ["a", "b", "c"] charList.remove("c") print (charList) # ['a', 'b']
7.2. pop()
It removes the specified item by it’s index. If index is not provided, it removes the last item from the list.
charList = ["a", "b", "c", "d"] charList.pop() # removes 'd' - last item print (charList) # ['a', 'b', 'c'] charList.pop(1) # removes 'b' print (charList) # ['a', 'c']
7.3. clear()
It empties the list.
charList = ["a", "b", "c", "d"] charList.clear() print (charList) # []
7.4. del keyword
It can be used to remove an item from list by it’s index. We can use it to delete the whole list as well.
charList = ["a", "b", "c", "d"] del charList[0] print (charList) # ['b', 'c', 'd'] del charList print (charList) # NameError: name 'charList' is not defined
8. Join two lists
We can join two given lists in Python using either "+"
operator or extend()
function.
charList = ["a", "b", "c"] numList = [1, 2, 3] list1 = charList + numList print (list1) # ['a', 'b', 'c', 1, 2, 3] charList.extend(numList) print (charList) # ['a', 'b', 'c', 1, 2, 3]
9. Python list methods
9.1. append()
Adds an element at the end of the list.
charList = ["a", "b", "c"] charList.append("d") print (charList) # ["a", "b", "c", "d"]
9.2. clear()
Removes all the elements from the list.
charList = ["a", "b", "c"] charList.clear() print (charList) # []
9.3. copy()
Returns a copy of the list.
charList = ["a", "b", "c"] newList = charList.copy() print (newList) # ["a", "b", "c"]
9.4. count()
Returns the number of elements with the specified value.
charList = ["a", "b", "c"] x = charList.count('a') print (x) # 1
9.5. extend()
Add the elements of a list to the end of the current list.
charList = ["a", "b", "c"] numList = [1, 2, 3] charList.extend(numList) print (charList) # ['a', 'b', 'c', 1, 2, 3]
9.6. index()
Returns the index of the first element with the specified value.
charList = ["a", "b", "c"] x = charList.index('a') print (x) # 0
9.7. insert()
Adds an element at the specified position.
charList = ["a", "b", "c"] charList.insert(3, 'd') print (charList) # ['a', 'b', 'c', 'd']
9.8. pop()
Removes the element at the specified position or end of the list.
charList = ["a", "b", "c", "d"] charList.pop() # removes 'd' - last item print (charList) # ['a', 'b', 'c'] charList.pop(1) # removes 'b' print (charList) # ['a', 'c']
9.9. remove()
Removes the item with the specified value.
charList = ["a", "b", "c", "d"] charList.remove('d') print (charList) # ['a', 'b', 'c']
9.10. reverse()
Reverses the order of items in the list.
charList = ["a", "b", "c", "d"] charList.reverse() print (charList) # ['d', 'c', 'b', 'a']
9.11. sort()
Sorts the given list in ascending order by default.
charList = ["a", "c", "b", "d"] charList.sort() print (charList) # ["a", "b", "c", "d"]
Happy Learning !!
Read More: