{"id":25776,"date":"2023-02-25T19:22:50","date_gmt":"2023-02-25T13:52:50","guid":{"rendered":"http:\/\/www.pythonpool.com\/?p=25776"},"modified":"2026-07-14T19:49:30","modified_gmt":"2026-07-14T14:19:30","slug":"filter-lambda-python","status":"publish","type":"post","link":"https:\/\/www.pythonpool.com\/filter-lambda-python\/","title":{"rendered":"Python filter() With lambda: Examples, Rules, and Better Alternatives"},"content":{"rendered":"

Quick answer:<\/strong> filter(function, iterable) returns a lazy iterator containing the items for which function returns a truthy value. A lambda can express a short predicate, but a list comprehension is often clearer when the condition is simple and the result should be a new list.<\/p>\n

\"Python
filter() keeps values whose predicate is truthy; convert the lazy result only when a concrete list or other collection is needed.<\/figcaption><\/figure>\n

Python filter()<\/code> selects items from an iterable by applying a test function to each item. The official Python filter()<\/code> documentation<\/a> defines it as an iterator over the elements for which the function is true. A lambda expression<\/a> is one compact way to write that test function.<\/p>\n

The basic pattern is filter(function, iterable)<\/code>. The result is an iterator, not a list. Convert it with list()<\/code> only when you actually need all matching items in memory.<\/p>\n

Use filter()<\/code> when the code reads clearly as \u201ckeep items matching this predicate.\u201d Use a list comprehension when the condition is easier to read inline. Both approaches are normal Python; the better choice is the one that makes the filtering rule obvious.<\/p>\n

Lambdas are best for short expressions. If the test needs several steps, logging, exception handling, or a useful name, write a regular function with def<\/code>.<\/p>\n

The most important detail is that filter()<\/code> keeps items based on truthiness. The predicate does not have to return the literal value True<\/code>; any truthy result keeps the item, and any falsey result removes it.<\/p>\n

\n
\n

Contents<\/p>\nToggle<\/span><\/path><\/svg><\/svg><\/span><\/span><\/span><\/a><\/span><\/div>\n