Replace safezip() by more informative error message in errorbar().

anntzer · anntzer · commit 30ef0b50299d · 2019-01-20T23:49:30.000+01:00
Currently, the error for mismatched shapes in errorbar is
```
ValueError: In safezip, len(args[0])=2 but len(args[1])=3
```
Replace it by
```
ValueError: The lengths of the data (2) and the error (3) do not match
```
and deprecate the not-so-informatively-named safezip.
diff --git a/doc/api/next_api_changes/2018-01-21-AL.rst b/doc/api/next_api_changes/2018-01-21-AL.rst
@@ -0,0 +1,5 @@
+Deprecations
+````````````
+
+``cbook.safezip`` is deprecated (manually check the lengths of the inputs
+instead, or rely on numpy to do it).
diff --git a/lib/matplotlib/axes/_axes.py b/lib/matplotlib/axes/_axes.py
@@ -3200,8 +3200,13 @@ def extract_err(err, data):
                 raise ValueError(
                     "err must be a scalar or a 1D or (2, n) array-like")
             # Using list comprehensions rather than arrays to preserve units.
-            low = [v - e for v, e in cbook.safezip(data, a)]
-            high = [v + e for v, e in cbook.safezip(data, b)]
+            for e in [a, b]:
+                if len(data) != len(e):
+                    raise ValueError(
+                        f"The lengths of the data ({len(data)}) and the "
+                        f"error {len(e)} do not match")
+            low = [v - e for v, e in zip(data, a)]
+            high = [v + e for v, e in zip(data, b)]
             return low, high
 
         if xerr is not None:
diff --git a/lib/matplotlib/cbook/__init__.py b/lib/matplotlib/cbook/__init__.py
@@ -776,6 +776,7 @@ def call(command, os_name):
 _safezip_msg = 'In safezip, len(args[0])=%d but len(args[%d])=%d'
 
 
+@deprecated("3.1")
 def safezip(*args):
     """make sure *args* are equal len before zipping"""
     Nx = len(args[0])
