Update flatten.py (keon#647)

Author: blucruz

Diff for: algorithms/arrays/flatten.py

@@ -11,7 +11,7 @@ def flatten(input_arr, output_arr=None):
     if output_arr is None:
         output_arr = []
     for ele in input_arr:
-        if isinstance(ele, Iterable):
+        if not isinstance(ele, str) and isinstance(ele, Iterable):
             flatten(ele, output_arr)    #tail-recursion
         else:
             output_arr.append(ele)      #produce the result
@@ -25,7 +25,7 @@ def flatten_iter(iterable):
     returns generator which produces one dimensional output.
     """
     for element in iterable:
-        if isinstance(element, Iterable):
+        if not isinstance(element, str) and isinstance(element, Iterable):
             yield from flatten_iter(element)    
         else:
             yield element