Update code in deep_flatten

snippets/deep_flatten.md

@@ -6,25 +6,14 @@ tags: list,recursion,intermediate
 Deep flattens a list.
 
 Use recursion. 
-Define a function, `spread`, that uses either `list.extend()` or `list.append()` on each element in a list to flatten it.
-Use `list.extend()` with an empty list and the `spread` function to flatten a list.
-Recursively flatten each element that is a list.
+Use `isinstance()` with `collections.abc.Iterable` to check if an element is iterable.
+If it is, apply `deep_flatten()` recursively, otherwise return `[lst]`.
 
 ```py
-def spread(arg):
-  ret = []
-  for i in arg:
-    if isinstance(i, list):
-      ret.extend(i)
-    else:
-      ret.append(i)
-  return ret
+from collections.abc import Iterable
 
 def deep_flatten(lst): 
-  result = []
-  result.extend(
-    spread(list(map(lambda x: deep_flatten(x) if type(x) == list else x, lst))))
-  return result
+  return [a for i in lst for a in deep_flatten(i)] if isinstance(lst, Iterable) else [lst]
 ```
 
 ```py