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Cleanup and document _plot_args() #19278

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Jan 12, 2021
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Cleanup and document _plot_args() #19278

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71 changes: 56 additions & 15 deletions lib/matplotlib/axes/_base.py
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Original file line number Diff line number Diff line change
Expand Up @@ -403,12 +403,53 @@ def _makefill(self, x, y, kw, kwargs):
return seg, kwargs

def _plot_args(self, tup, kwargs, return_kwargs=False):
"""
Process the arguments of ``plot([x], y, [fmt], **kwargs)`` calls.

This processes a single set of ([x], y, [fmt]) parameters; i.e. for
``plot(x, y, x2, y2)`` it will be called twice. Once for (x, y) and
once for (x2, y2).

x and y may be 2D and thus can still represent multiple datasets.

For multiple datasets, if the keyword argument *label* is a list, this
will unpack the list and assign the individual labels to the datasets.

Parameters
----------
tup : tuple
A tuple of the positional parameters. This can be one of

- (y,)
- (x, y)
- (y, fmt)
- (x, y, fmt)

kwargs : dict
The keyword arguments passed to ``plot()``.

return_kwargs : bool
If true, return the effective keyword arguments after label
unpacking as well.

Returns
-------
result
If *return_kwargs* is false, a list of Artists representing the
dataset(s).
If *return_kwargs* is true, a list of (Artist, effective_kwargs)
representing the dataset(s). See *return_kwargs*.
The Artist is either `.Line2D` (if called from ``plot()``) or
`.Polygon` otherwise.
"""
if len(tup) > 1 and isinstance(tup[-1], str):
linestyle, marker, color = _process_plot_format(tup[-1])
tup = tup[:-1]
# xy is tup with fmt stripped (could still be (y,) only)
*xy, fmt = tup
linestyle, marker, color = _process_plot_format(fmt)
elif len(tup) == 3:
raise ValueError('third arg must be a format string')
else:
xy = tup
linestyle, marker, color = None, None, None

# Don't allow any None value; these would be up-converted to one
Expand All @@ -417,16 +458,16 @@ def _plot_args(self, tup, kwargs, return_kwargs=False):
raise ValueError("x, y, and format string must not be None")
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This would never have checked whether fmt is None, because of the first if, is it not?

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For (x, y, None), you ended up with the "third arg must be a format string" error. But for (y, None) this check triggers.

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Ah yes, because the length checks are different.


kw = {}
for k, v in zip(('linestyle', 'marker', 'color'),
(linestyle, marker, color)):
if v is not None:
kw[k] = v

if len(tup) == 2:
x = _check_1d(tup[0])
y = _check_1d(tup[-1])
for prop_name, val in zip(('linestyle', 'marker', 'color'),
(linestyle, marker, color)):
if val is not None:
kw[prop_name] = val

if len(xy) == 2:
x = _check_1d(xy[0])
y = _check_1d(xy[1])
else:
x, y = index_of(tup[-1])
x, y = index_of(xy[-1])

if self.axes.xaxis is not None:
self.axes.xaxis.update_units(x)
Expand All @@ -445,10 +486,10 @@ def _plot_args(self, tup, kwargs, return_kwargs=False):
y = y[:, np.newaxis]

if self.command == 'plot':
func = self._makeline
make_artist = self._makeline
else:
kw['closed'] = kwargs.get('closed', True)
func = self._makefill
make_artist = self._makefill

ncx, ncy = x.shape[1], y.shape[1]
if ncx > 1 and ncy > 1 and ncx != ncy:
Expand All @@ -465,8 +506,8 @@ def _plot_args(self, tup, kwargs, return_kwargs=False):
else:
labels = [label] * n_datasets

result = (func(x[:, j % ncx], y[:, j % ncy], kw,
{**kwargs, 'label': label})
result = (make_artist(x[:, j % ncx], y[:, j % ncy], kw,
{**kwargs, 'label': label})
for j, label in enumerate(labels))

if return_kwargs:
Expand Down