List ComprehensionsBeginner
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pythonHow do List, Dict, and Set Comprehensions work in Python and when should they be avoided?
Explanation & Concept
Comprehensions provide a concise syntactic way to build new sequences from existing iterables. They are faster than manual `for` loops because the looping bytecode executes directly in optimized C.
Avoid them when the logic has complex nested conditions or multiple side effects, which impairs readability.
Code Example
python
# 1. List Comprehension with filtering
numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
evens_squared = [n ** 2 for n in numbers if n % 2 == 0]
# [4, 16, 36, 64, 100]
# 2. Dict Comprehension
users = [("u1", "Alice"), ("u2", "Bob")]
user_lookup = {uid: name for uid, name in users}
# {'u1': 'Alice', 'u2': 'Bob'}
# 3. Set Comprehension (Automatic Deduplication)
words = ["apple", "banana", "apple", "cherry"]
unique_lengths = {len(w) for w in words}
# {5, 6}How It Works & Key Takeaways
Comprehensions express mapping and filtering declaratively in a single readable line without temporary variable allocation.
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