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Python Set comprehensions

Set comprehensions in Python provide a concise way to create sets. Similar to list and dictionary comprehensions, set comprehensions allow you to generate a set by applying an expression to each item in an iterable and optionally including conditional logic to filter items.

Basic Syntax

The basic syntax for a set comprehension is:

{expression for item in iterable}

This translates to: "Generate a set by evaluating the expression for each item in the iterable."

Examples

  1. Simple Set Comprehension:

    Create a set of squares of numbers from 0 to 9.

squares = {x**2 for x in range(10)}
print(squares)  # Output: {0, 1, 4, 36, 9, 16, 49, 64, 25, 81}

2. Set Comprehension with Condition:

Create a set of even numbers from 0 to 9.

evens = {x for x in range(10) if x % 2 == 0} print(evens) # Output: {0, 2, 4, 6, 8}

3. Using a Function in Set Comprehension:

Create a set of lengths of strings in a list.

words = ["apple", "banana", "cherry", "date"] lengths = {len(word) for word in words} print(lengths) # Output: {8, 5, 6}

4. Removing Duplicates with Set Comprehension:

Create a set from a list to remove duplicates.

nums = [1, 2, 2, 3, 4, 4, 5] unique_nums = {x for x in nums} print(unique_nums) # Output: {1, 2, 3, 4, 5}


Nested Set Comprehensions

You can also create sets of sets using nested comprehensions, although this is less common due to the constraints on set elements (they must be immutable).

nested_set = {frozenset({i + j for j in range(3)}) for i in range(3)} print(nested_set) # Output: {frozenset({0, 1, 2}), frozenset({1, 2, 3}), frozenset({2, 3, 4})}

Set Comprehension with Complex Conditions

You can include more complex conditions within the comprehension.

filtered_set = {x for x in range(20) if x % 2 == 0 and x % 3 == 0} print(filtered_set) # Output: {0, 6, 12, 18}

Comparison with Other Comprehensions

  • List Comprehensions: Use [] for lists.
  • Dictionary Comprehensions: Use {} with key-value pairs.
  • Set Comprehensions: Use {} with single expressions.

Summary

  • Basic Syntax: {expression for item in iterable}
  • Conditionals: {expression for item in iterable if condition}
  • Functions in Comprehensions: Apply functions within comprehensions.
  • Removing Duplicates: Use set comprehensions to create sets from lists, automatically removing duplicates.
  • Nested Comprehensions: Create sets within sets using frozenset.

Set comprehensions provide a powerful, readable, and efficient way to create sets in Python. They are useful for generating sets dynamically, removing duplicates, and applying conditions to filter items.

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