The Ultimate Guide to Python Comprehensions: Sub-stack Edition

Beyond Lists: Exploring Other Python Comprehensions

Comprehension: In Python, comprehensions provide a concise way to create collections (like lists, dictionaries, sets, and tuples) by using a single line of code. Comprehensions can be used to apply operations, filter data, and create new collections with less code.

1. List Comprehension:

Definition: A list comprehension creates a new list by applying an expression to each item in an iterable.

# Syntax:
[expression for item in iterable if condition]

# Trick: Use list comprehension to flatten nested lists.
matrix = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
flat = [num for row in matrix for num in row]
# Output: [1, 2, 3, 4, 5, 6, 7, 8, 9]&

2. Dictionary Comprehension:

Definition: A dictionary comprehension creates a new dictionary by applying an expression to each key-value pair in an iterable.

# Syntax:
{key_expression: value_expression for item in iterable if condition}

# Trick: Inverting keys and values in a dictionary.
original_dict = {'a': 1, 'b': 2, 'c': 3}
inverted_dict = {v: k for k, v in original_dict.items()}
# Output: {1: 'a', 2: 'b', 3: 'c'}

3. Set Comprehension:

Definition: A set comprehension creates a new set by applying an expression to each item in an iterable. Since sets automatically handle duplicates, this is a great way to ensure unique items.

# Syntax:
{expression for item in iterable if condition}

# Trick: Extract unique vowels from a string.
vowels = {char for char in 'pythoncomprehension' if char in 'aeiou'}
# Output: {'e', 'o', 'i'}

4. Tuple Comprehension (Generator Expression):

Definition: While Python does not have tuple comprehensions, you can create a tuple by using a generator expression, which is similar in syntax to a comprehension but uses parentheses instead of square brackets. This generates items one at a time and is more memory efficient.

# Syntax:
(expression for item in iterable if condition)

# Trick: Generate a sequence of tuples.
pairs = ((x, x**2) for x in range(5))
pairs_tuple = tuple(pairs)
# Output: ((0, 0), (1, 1), (2, 4), (3, 9), (4, 16))

Click on `Buy Me Book` because Learning is better with Books! Help me write more in-depth articles.

Summary of Tricks:

• List comprehension can be used to flatten nested lists.

• Dictionary comprehension can invert keys and values.

• Set comprehension automatically removes duplicates.

• Tuple comprehension (via generator expressions) is memory efficient and can be converted to a tuple.