Added Flatten()

snippets/flatten.md

@@ -0,0 +1,17 @@
+---
+title: flatten
+tags: list,intermediate
+---
+
+Flattens a list of lists.
+
+Use nested list comprehension to extract each value from sub-lists in order.
+
+```py
+def flatten(lst):
+  return [x for y in lst for x in y]
+```
+
+```py
+flatten([[1,2,3,4],[5,6,7,8]]) # [1, 2, 3, 4, 5, 6, 7, 8]
+```