Python List Comprehensions Explained
List comprehensions look like a one-line trick but they are a full mini-language. Here is a clear breakdown of the syntax and the patterns I use. List comprehensions are often taught as a shortcut for writing loops in one line, but that framing undersells them. A list comprehension is its own small language with rules about ordering, scoping, and evaluation that differ from a regular for loop. Once I understood the rules, I stopped writing comprehensions that surprised me and started using them where they genuinely improve readability. The Core Pattern Every list comprehension has three parts: an output expression, a for clause, and zero or more if clauses. The output expression is evaluated for each item that survives the filters, and the results are collected into a new list. The order matters: expression first, then the for, then the filters. # [expression for item in iterable if condition] squares = [x ** 2 for x in range(10)] evens = [x for x in range(20) if x % 2 == 0] The output expression can be anything, including function calls and conditional expressions. A conditional expression inside the output position is different from an if filter:…