Merge pull request matplotlib#9337 from matplotlib/auto-backport-of-pr-9242

Backport PR matplotlib#9242 on branch v2.1.x

Author: dstansby

lib/matplotlib/axes/_axes.py

@@ -4,7 +4,6 @@
 import six
 from six.moves import xrange, zip, zip_longest
 
-from collections import Sized
 import functools
 import itertools
 import math
@@ -3025,8 +3024,7 @@ def extract_err(err, data):
             # special case for empty lists
             if len(err) > 1:
                 fe = safe_first_element(err)
-                if (len(err) != len(data)
-                        or isinstance(fe, Sized) and len(fe) > 1):
+                if (len(err) != len(data) or np.size(fe) > 1):
                     raise ValueError("err must be [ scalar | N, Nx1 "
                                      "or 2xN array-like ]")
             # using list comps rather than arrays to preserve units