Reorganize snippets

python/s/flatten.md

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+---
+title: Flatten list
+type: snippet
+language: python
+tags: [list]
+cover: jars-on-shelf
+dateModified: 2020-11-02T19:27:53+02:00
+---
+
+Flattens a list of lists once.
+
+- Use a 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]
+```