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Python is a convenient language that’s often used for scripting, data science, and web development.

In this article, we’ll look at the many things that we can do with Python lists.

Sorting the Values in a List with the sort() Method

We can use the list sort method to sort a list. It works with any object, including strings and numbers.

For example, we can use it as follows:

fruits = ['apple', 'orange', 'orange', 'grape', 'pear']  
fruits.sort()

The sorting is done in place. So it sorts the list that it’s called on.

Therefore, we get:

['apple', 'grape', 'orange', 'orange', 'pear']

as the new value of fruits.

With numbers, we can write:

nums = [5,3,4,6,7]  
nums.sort()

Then the new value of nums is:

[3, 4, 5, 6, 7]

We can’t sort lists that have mixed data types.

For example, the following list:

mixed = ['apple', 'orange',3,2,1]  
mixed.sort()

We’ll get:

TypeError: '<' not supported between instances of 'int' and 'str'

since sort can’t compare the entries.

Reversing the Values in a List with the reverse() Method

The reverse method reverses a list in place. It can also be done with string and number arrays.

For instance, we can write:

fruits = ['apple', 'orange', 'orange', 'grape', 'pear']  
fruits.reverse()

Then the new value of fruits is:

['pear', 'grape', 'orange', 'orange', 'apple']

Likewise, we can do the same with a number list:

nums = [5,3,4,6,7]  
nums.reverse()

Then we get:

[7, 6, 4, 3, 5]

as the new value of nums.

Emptying a List with clear()

We can call clear on a list to clear all entries from a list.

For instance, we can call it as follows:

nums = [5,3,4,6,7]  
nums.clear()

Then we get that the new value of nums is an empty list.

Remove the Last Element of a List with pop()

We can call pop on a list to remove the last item off a list.

For instance, we can write the following:

nums = [5,3,4,6,7]  
nums.pop()

to remove 7 from nums.

Counting the Number of Times an Item Appears on a List with count()

The count method takes an element that we want to search for in a list.

For instance, we can use it as follows:

fruits = ['apple', 'orange', 'orange', 'grape', 'pear']  
orange_count = fruits.count('orange')

orange_count should be 2 since 'orange' appeared twice on the list.

Shallow Copying a List with copy()

The copy method creates a shallow copy of the array it’s called on and returns it. This is the same as a[:].

A shallow copy means only the top-level items are copied. Nested items are still referencing the original items.

For instance, given that we have the following code:

fruits = ['apple', 'orange', 'orange', 'grape', 'pear']  
fruits_copy = fruits.copy()  
fruits_copy.append('banana')

We should see that the value of fruits is:

['apple', 'orange', 'orange', 'grape', 'pear']

and the value of fruits_copy is:

['apple', 'orange', 'orange', 'grape', 'pear', 'banana']

This is because we made a copy of the fruits list by calling copy. Therefore, fruits_copy is referencing a new list with the same entries as fruits in the second line.

List Comprehensions

We can use the list comprehension syntax to create a list by mapping list items by calling a function to do the mapping.

For instance, we can write:

cubes = [x**3 for x in range(10)]

to create an array with each entry a cube of the entry returned from range(10) .

Therefore, we should get:

[0, 1, 8, 27, 64, 125, 216, 343, 512, 729]

as the value of cubes since 0**3 is 0, 1**3 is 1, 2**3 is 8, and so on.

We can also use it to returns a new list with some items filtered out as follows:

nums = [-3,5,6]  
positive_nums = [x for x in nums if x > 0]

The code above takes all the numbers that are bigger than 0 on the list and returns it.

Therefore, we should get:

[5, 6]

as the value of positive_nums.

Conclusion

Python lists have lots of methods to do various operations.

We can sort lists with sort, remove the last item from a list with pop, count the number of items we’re looking for with count, and empty a list with clear.

Python also has the list comprehension syntax to generate a list from another list.