Update some snippets

snippets/deep_flatten.md

@@ -1,27 +1,30 @@
 ---
 title: deep_flatten
-tags: list
+tags: list,recursion,intermediate
 ---
+
 Deep flattens a list.
 
-Use recursion. Use `list.extend()` with an empty list (`result`) and the spread function to flatten a list. Recursively flatten each element that is 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.
 
 ```py
 def spread(arg):
-    ret = []
-    for i in arg:
-        if isinstance(i, list):
-            ret.extend(i)
-        else:
-            ret.append(i)
-    return ret
-
+  ret = []
+  for i in arg:
+    if isinstance(i, list):
+      ret.extend(i)
+    else:
+      ret.append(i)
+  return ret
 
 def deep_flatten(lst):
-    result = []
-    result.extend(
-        spread(list(map(lambda x: deep_flatten(x) if type(x) == list else x, lst))))
-    return result
+  result = []
+  result.extend(
+    spread(list(map(lambda x: deep_flatten(x) if type(x) == list else x, lst))))
+  return result
 ```
 
 ```py