Keep even numbers
Input
make_filter(lambda x: x % 2 == 0)([1, 2, 3, 4])
Output
[2, 4]
The produced function filters the iterable to include only even numbers.
Full lesson preview
Build a reusable filter function with lambda
Create a factory that returns reusable filter functions (optionally negated) to apply to any iterable.
Python practice32 minFunctions as Objects (Lambda, Map/Filter)AdvancedLast updated March 20, 2026
Problem statement
Filtering logic is frequently reused across different parts of a program. Rather than repeating predicates and list comprehensions, build a factory that produces reusable filter functions:
- make_filter(predicate, negate=False) should return a function that accepts an iterable and returns a list of items where predicate(item) is True (or False if negate is True).
- The returned function must accept any iterable (including generators) and always return a list.
This pattern makes predicates first-class values that can be stored and reused.
Task
Implement make_filter(predicate, negate=False) that returns a callable expecting an iterable and returning a filtered list.
Examples
Input format
Two parameters to the factory: predicate (callable) and optional negate (bool). The returned function accepts one parameter: an iterable.
Output format
The returned function produces a Python list of filtered items.
Constraints
- The returned function must accept any iterable and must return a list.
- Do not use print; just return the filtered list.
Samples
Sample 1
Input
make_filter(lambda s: 'ap' in s.lower())(['Apple','banana','Grape'])
Output
['Apple', 'Grape']
Case-insensitive substring match; 'Apple' and 'Grape' include 'ap'.