difference_by

snippets/difference_by.md

@@ -1,7 +1,12 @@
 ### difference_by
-``` python
+
+Returns the difference between two list, after applying the provided function to each list element of both.
+
+Create a `set` by applying `fn` to each element in `b`, then use list comprehension in combination with fn on a to only keep values not contained in the previously created `set`.
+
+```python
 def difference_by(a, b, fn):
-    b = set(map(fn,b))
+    b = set(map(fn, b))
     return [item for item in a if fn(item) not in b]
 ```