Python List Operations Cheatsheet

This cheatsheet provides a comprehensive guide to common list operations in Python, including how to remove empty items, add or remove elements, and perform slicing, sorting, and more.

1. Removing Empty Items from a List

You can use either list comprehension or the filter() function to remove empty items from a list.

Using List Comprehension:

my_list = ["apple", "", "banana", "", "cherry", ""]
my_list = [item for item in my_list if item]
print(my_list)  # Output: ['apple', 'banana', 'cherry']

Using `filter()`:

my_list = ["apple", "", "banana", "", "cherry", ""]
my_list = list(filter(None, my_list))
print(my_list)  # Output: ['apple', 'banana', 'cherry']

2. Adding Items to a List

Append an item to the end of the list:

my_list = ["apple", "banana"]
my_list.append("cherry")
print(my_list)  # Output: ['apple', 'banana', 'cherry']

Insert an item at a specific position:

my_list = ["apple", "banana"]
my_list.insert(1, "cherry")
print(my_list)  # Output: ['apple', 'cherry', 'banana']

Extend a list with another list:

my_list = ["apple", "banana"]
my_list.extend(["cherry", "orange"])
print(my_list)  # Output: ['apple', 'banana', 'cherry', 'orange']

3. Removing Items from a List

Remove an item by value:

my_list = ["apple", "banana", "cherry"]
my_list.remove("banana")
print(my_list)  # Output: ['apple', 'cherry']

Remove an item by index:

my_list = ["apple", "banana", "cherry"]
my_list.pop(1)
print(my_list)  # Output: ['apple', 'cherry']

Clear all items from the list:

my_list = ["apple", "banana", "cherry"]
my_list.clear()
print(my_list)  # Output: []

4. Slicing a List

Get a sublist by slicing:

my_list = ["apple", "banana", "cherry", "orange", "kiwi"]
sub_list = my_list[1:4]
print(sub_list)  # Output: ['banana', 'cherry', 'orange']

Get the last three items of the list:

my_list = ["apple", "banana", "cherry", "orange", "kiwi"]
print(my_list[-3:])  # Output: ['cherry', 'orange', 'kiwi']

5. Sorting a List

Sort a list in ascending order:

my_list = [3, 1, 4, 1, 5, 9]
my_list.sort()
print(my_list)  # Output: [1, 1, 3, 4, 5, 9]

Sort a list in descending order:

my_list = [3, 1, 4, 1, 5, 9]
my_list.sort(reverse=True)
print(my_list)  # Output: [9, 5, 4, 3, 1, 1]

Sort a list of strings alphabetically:

my_list = ["banana", "apple", "cherry"]
my_list.sort()
print(my_list)  # Output: ['apple', 'banana', 'cherry']

Sort a list without modifying the original list:

my_list = [3, 1, 4, 1, 5, 9]
sorted_list = sorted(my_list)
print(sorted_list)  # Output: [1, 1, 3, 4, 5, 9]

6. Checking for Items in a List

Check if an item exists in a list:

my_list = ["apple", "banana", "cherry"]
print("banana" in my_list)  # Output: True

Get the index of an item:

my_list = ["apple", "banana", "cherry"]
index = my_list.index("banana")
print(index)  # Output: 1

7. List Comprehension

Basic list comprehension:

squared = [x**2 for x in range(5)]
print(squared)  # Output: [0, 1, 4, 9, 16]

Conditional list comprehension:

even_numbers = [x for x in range(10) if x % 2 == 0]
print(even_numbers)  # Output: [0, 2, 4, 6, 8]

8. Combining Lists

Concatenate two lists:

list1 = [1, 2, 3]
list2 = [4, 5, 6]
combined_list = list1 + list2
print(combined_list)  # Output: [1, 2, 3, 4, 5, 6]

Zip two lists into pairs:

list1 = [1, 2, 3]
list2 = ["a", "b", "c"]
zipped = list(zip(list1, list2))
print(zipped)  # Output: [(1, 'a'), (2, 'b'), (3, 'c')]

9. Other Useful List Operations

Get the length of a list:

my_list = ["apple", "banana", "cherry"]
print(len(my_list))  # Output: 3

Count occurrences of an item:

my_list = ["apple", "banana", "cherry", "banana"]
print(my_list.count("banana"))  # Output: 2

Reverse a list:

my_list = [1, 2, 3, 4]
my_list.reverse()
print(my_list)  # Output: [4, 3, 2, 1]

10. Copying Lists

Shallow copy a list:

my_list = ["apple", "banana", "cherry"]
copy_list = my_list.copy()
print(copy_list)  # Output: ['apple', 'banana', 'cherry']

Conclusion

This Python list operations cheatsheet covers a wide range of list methods and functionalities. Whether you're adding, removing, slicing, or sorting, Python's list methods are intuitive and powerful. Use this guide as a quick reference for your day-to-day Python programming tasks involving lists.