filter() function constructs an iterator from elements of an iterable for which a function returns true. We can understand that
filter will test every element of iterators to be true or not.
A Quick Example
marks = [5, 7, 2, 8, 9] def is_pass_test(x): if m < 5: return False else: return True passes = filter(is_pass_test, marks) print(list(passes)) /* Result: [7, 8, 9] */
Definition and Usage
filter() syntax is as follows:
- function: The function will be executed for each element of iterable.
- iterable: The iterable to be filtered.
Python Filter Examples
Example 1: Using lambda function with filter()
We can make above example a lot shorter by using
marks = [5, 7, 2, 8, 9] passes = filter(lambda x: x > 5, marks) print(list(passes)) /* Result: [7, 8, 9] */
You don’t know what is
lambda, don’t worry, read our article to understand it (What’s lambda syntax in Python)
Example 2: Passing None function to filter()
datas = [5, False, '', True, 'Filtered', None] passes = filter(None, datas) print(list(passes)) /* Result: [5, True, 'Filtered'] */
In this example, we passed None as a function parameter. However it is not a real None value, it means a default function. In this case, a default function equal to
lambda x: x
As our goal to build a short and understandable tutorial. However, in case you would like to learn deeper, you should read below references: