In this guide, we will discuss lists in Python. A list is a data type that allows you to store various types data in it. List is a compound data type which means you can have different-2 data types under a list, for example we can have integer, float and string items in a same list.
1. Create a List in Python
Lets see how to create a list in Python. To create a list all you have to do is to place the items inside a square bracket [] separated by comma ,.
# list of floats num_list = [11.22, 9.9, 78.34, 12.0] # list of int, float and strings mix_list = [1.13, 2, 5, "beginnersbook", 100, "hi"] # an empty list nodata_list = []
As we have seen above, a list can have data items of same type or different types. This is the reason list comes under compound data type.
2. Accessing the items of a list
Syntax to access the list items:
list_name[index]
Example:
# a list of numbers numbers = [11, 22, 33, 100, 200, 300] # prints 11 print(numbers[0]) # prints 300 print(numbers[5]) # prints 22 print(numbers[1])
Output:
11 300 22
Points to Note:
1. The index cannot be a float number.
For example:
# a list of numbers numbers = [11, 22, 33, 100, 200, 300] # error print(numbers[1.0])
Output:
TypeError: list indices must be integers or slices, not float
2. The index must be in range to avoid IndexError. The range of the index of a list having 10 elements is 0 to 9, if we go beyond 9 then we will get IndexError. However if we go below 0 then it would not cause issue in certain cases, we will discuss that in our next section.
For example:
# a list of numbers numbers = [11, 22, 33, 100, 200, 300] # error print(numbers[6])
Output:
IndexError: list index out of range
3. Negative Index to access the list items from the end
Unlike other programming languages where negative index may cause issue, Python allows you to use negative indexes. The idea behind this to allow you to access the list elements starting from the end. For example an index of -1 would access the last element of the list, -2 second last, -3 third last and so on.
3.1 Example of Negative indexes in Python
# a list of strings my_list = ["hello", "world", "hi", "bye"] # prints "bye" print(my_list[-1]) # prints "world" print(my_list[-3]) # prints "hello" print(my_list[-4])
Output:
bye world hello
4. How to get a sublist in Python using slicing
We can get a sublist from a list in Python using slicing operation. Lets say we have a list n_list having 10 elements, then we can slice this list using colon : operator. Lets take an example to understand this:
4.1 Slicing example
# list of numbers n_list = [1, 2, 3, 4, 5, 6, 7] # list items from 2nd to 3rd print(n_list[1:3]) # list items from beginning to 3rd print(n_list[:3]) # list items from 4th to end of list print(n_list[3:]) # Whole list print(n_list[:])
Output:
[2, 3] [1, 2, 3] [4, 5, 6, 7] [1, 2, 3, 4, 5, 6, 7]
5. List Operations
There are various operations that we can perform on Lists.
5.1 Addition
There are several ways you can add elements to a list.
# list of numbers n_list = [1, 2, 3, 4] # 1. adding item at the desired location # adding element 100 at the fourth location n_list.insert(3, 100) # list: [1, 2, 3, 100, 4] print(n_list) # 2. adding element at the end of the list n_list.append(99) # list: [1, 2, 3, 100, 4, 99] print(n_list) # 3. adding several elements at the end of list # the following statement can also be written like this: # n_list + [11, 22] n_list.extend([11, 22]) # list: [1, 2, 3, 100, 4, 99, 11, 22] print(n_list)
Output:
[1, 2, 3, 100, 4] [1, 2, 3, 100, 4, 99] [1, 2, 3, 100, 4, 99, 11, 22]
5.2 Update elements
We can change the values of elements in a List. Lets take an example to understand this:
# list of numbers n_list = [1, 2, 3, 4] # Changing the value of 3rd item n_list[2] = 100 # list: [1, 2, 100, 4] print(n_list) # Changing the values of 2nd to fourth items n_list[1:4] = [11, 22, 33] # list: [1, 11, 22, 33] print(n_list)
Output:
[1, 2, 100, 4] [1, 11, 22, 33]
5.3 Delete elements
# list of numbers n_list = [1, 2, 3, 4, 5, 6] # Deleting 2nd element del n_list[1] # list: [1, 3, 4, 5, 6] print(n_list) # Deleting elements from 3rd to 4th del n_list[2:4] # list: [1, 3, 6] print(n_list) # Deleting the whole list del n_list
Output:
[1, 3, 4, 5, 6] [1, 3, 6]
5.4 Deleting elements using remove(), pop() and clear() methods
remove(item): Removes specified item from list.
pop(index): Removes the element from the given index.
pop(): Removes the last element.
clear(): Removes all the elements from the list.
# list of chars
ch_list = ['A', 'F', 'B', 'Z', 'O', 'L']
# Deleting the element with value 'B'
ch_list.remove('B')
# list: ['A', 'F', 'Z', 'O', 'L']
print(ch_list)
# Deleting 2nd element
ch_list.pop(1)
# list: ['A', 'Z', 'O', 'L']
print(ch_list)
# Deleting all the elements
ch_list.clear()
# list: []
print(ch_list)
Output:
['A', 'F', 'Z', 'O', 'L'] ['A', 'Z', 'O', 'L'] []
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