The Filter Function

Basic understanding of the `filter` function.

Transcript

1. Handle Nonetype objects # Remove Nonetypes before using Max L = [None, None, None] max([i for i in L if is not None], default=None) @eloy · python 3.6 · 2018 1/14
2. Using the filter function # Remove Nonetypes before using Max max(filter(None, L), default=None) @eloy · python 3.6 · 2018 2/14
3. filter() Keep item if 'True'
4. Filter function # Takes a function and an iterable filter(<function>, <iterable>) @eloy · python 3.6 · 2018 4/14
5. Let's try an example # Anything greater than 2 shall pass def greater_than_2(item): """Assume item is integer.""" return item > 2 items = filter(greater_than_2, [1, 2, 3, 4]) @eloy · python 3.6 · 2018 5/14
6. Using the filter function # Remove Nonetypes before using Max max(filter(None, L), default=None) @eloy · python 3.6 · 2018 6/14
7. @eloy · python 3.6 · 2018 7/14
8. Identity function # If NO function is passed, then we use the "Identity function" filter(None, iterable) # Identity function = Is this Truthy or Falsey? truthy_items = [True, object, 'a', '0', 1, 2, -1] falsey_items = [False, None, '', "", 0] @eloy · python 3.6 · 2018 8/14
9. Testing identity function # Everything makes it through the filter everything = filter(None, [True, object, 'a', 1]) # Nothing makes it through the filter nothing = filter(None, [False, None, '', "", 0]) @eloy · python 3.6 · 2018 9/14
10. Lets make a None function # Anything greater than 2 shall pass def fake_none(item): """Test truthiness.""" return bool(item) items = filter(fake_none, [1, 2, 3, 4]) @eloy · python 3.6 · 2018 10/14
11. Filter returns an iterable iterable = filter(None, truthy_items) @eloy · python 3.6 · 2018 11/14
12. Still an iterable iterable = list(filter(None, truthy_items)) @eloy · python 3.6 · 2018 12/14
13. Technically an iterator iterator = filter(None, truthy_items) @eloy · python 3.6 · 2018 13/14
14. Do you know the difference? 4 iterable 4 lazy iterable 4 iterator 4 range We'll talk about this next month :D @eloy · python 3.6 · 2018 14/14