DOC: better argcheck bar

[jklymak]

PR Summary

Closes #13142

This checks that x and width in bar can be subtracted and emits a more useful message than before.

The underlying issue is that width=0.8, which has no units, and in this case x has datetime64 units.

Code

import pandas as pd
import matplotlib.pyplot as plt
from datetime import datetime

def timestamp_to_datetime(raw):
    return datetime.fromtimestamp(raw/1000)

df = pd.DataFrame([{
    'timestamp': 1500854400000,
    'activity': 5},
{
    'timestamp': 1500940800000,
    'activity': 6
}])
df['date'] = df['timestamp'].apply(timestamp_to_datetime)

plt.figure(figsize=(20,10))
plt.bar(df['date'], df['activity'])
plt.show();

Before:

Traceback (most recent call last):
  File "testBarDT.py", line 24, in <module>
    plt.bar(df['date'], df['activity'])
  File "/Users/jklymak/matplotlib/lib/matplotlib/pyplot.py", line 2438, in bar
    **({"data": data} if data is not None else {}), **kwargs)
  File "/Users/jklymak/matplotlib/lib/matplotlib/__init__.py", line 1778, in inner
    return func(ax, *args, **kwargs)
  File "/Users/jklymak/matplotlib/lib/matplotlib/axes/_axes.py", line 2277, in bar
    left = x - width / 2
TypeError: ufunc subtract cannot use operands with types dtype('<M8[ns]') and dtype('float64')

After

Traceback (most recent call last):
  File "/Users/jklymak/matplotlib/lib/matplotlib/axes/_axes.py", line 2278, in bar
    left = x - width / 2
TypeError: ufunc subtract cannot use operands with types dtype('<M8[ns]') and dtype('float64')

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "testBarDT.py", line 18, in <module>
    plt.bar(df['date'], df['activity'])
  File "/Users/jklymak/matplotlib/lib/matplotlib/pyplot.py", line 2438, in bar
    **({"data": data} if data is not None else {}), **kwargs)
  File "/Users/jklymak/matplotlib/lib/matplotlib/__init__.py", line 1778, in inner
    return func(ax, *args, **kwargs)
  File "/Users/jklymak/matplotlib/lib/matplotlib/axes/_axes.py", line 2282, in bar
    f'({width.dtype}) are incompatible') from e
ValueError: the dtypes of parameters x (datetime64[ns]) and width (float64) are incompatible

PR Checklist

• Has Pytest style unit tests
• Code is Flake 8 compliant
• New features are documented, with examples if plot related
• Documentation is sphinx and numpydoc compliant
• Added an entry to doc/users/next_whats_new/ if major new feature (follow instructions in README.rst there)
• Documented in doc/api/api_changes.rst if API changed in a backward-incompatible way

[NelleV]

I've fixed the pep8 errors directly. I'll merge once test pass!

Thanks @jklymak !

[jklymak]

Ooops, sorry missed fixing those. Feel free to squash merge, or I can self-merge when CI passes.

[dstansby]

Just restarted the tests since they're fixed, anyone feel free to merge if/when they pass!

[NelleV]

Thanks!