Clarify error when plot() args have bad shapes.

[anntzer]

When I see the error "x and y must have the same dimensions", typically the first thing I do is to re-run the thing with a print of the shapes just before the call to plot() (or do this via pdb), and then I think about what went wrong. This is a minor patch that would save this step.

[mdboom]

Thanks for this. The double parens are a bit jarring though, and this gives more info than one needs. Maybe:

"x and y must have same first dimension.  Got {} and {}.".format(x.shape[0], y.shape[0])

[WeatherGod]

Nah, I like seeing the whole shape info. Just having the first dimension of
the shape doesn't always clue you into what went wrong. Perhaps I
transposed one of the arrays? Maybe I passed in a completely different
array than I intended? Only printing the first dimensions size will likely
still have me going back and printing out the full shape info.

That said, I would like to see the original message kept intact in the
beginning of the string, only adding the new stuff at the end.

On Thu, Dec 3, 2015 at 8:03 AM, Michael Droettboom <notifications@github.com

wrote:

In lib/matplotlib/axes/_base.py
#5607 (comment):

@@ -220,9 +220,11 @@ def _xy_from_xy(self, x, y):
x = _check_1d(x)
y = _check_1d(y)
if x.shape[0] != y.shape[0]:

•        raise ValueError("x and y must have same first dimension")
  

•        raise ValueError("x (shape: {}) and y (shape: {}) must have same "
  

•                         "first dimension".format(x.shape, y.shape))
  

Thanks for this. The double parens are a bit jarring though, and this
gives more info than one needs. Maybe:

"x and y must have same first dimension. Got {} and {}.".format(x.shape[0], y.shape[0])

—
Reply to this email directly or view it on GitHub
https://github.com/matplotlib/matplotlib/pull/5607/files#r46548308.

[tacaswell]

I am with @WeatherGod on both points.

[tacaswell]

I am 50/50 on backporting this to 2.0

[anntzer]

Updated error message.