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Create axline() using slope #16337

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Merged
merged 1 commit into from
Apr 2, 2020
Merged

Create axline() using slope #16337

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38 changes: 32 additions & 6 deletions lib/matplotlib/axes/_axes.py
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Original file line number Diff line number Diff line change
Expand Up @@ -905,18 +905,27 @@ def axvline(self, x=0, ymin=0, ymax=1, **kwargs):
return l

@docstring.dedent_interpd
def axline(self, xy1, xy2, **kwargs):
def axline(self, xy1, xy2=None, *, slope=None, **kwargs):
"""
Add an infinitely long straight line that passes through two points.
Add an infinitely long straight line.

The line can be defined either by two points *xy1* and *xy2*, or
by one point *xy1* and a *slope*.

This draws a straight line "on the screen", regardless of the x and y
scales, and is thus also suitable for drawing exponential decays in
semilog plots, power laws in loglog plots, etc.
semilog plots, power laws in loglog plots, etc. However, *slope*
should only be used with linear scales; It has no clear meaning for
all other scales, and thus the behavior is undefined. Please specify
the line using the points *xy1*, *xy2* for non-linear scales.

Parameters
----------
xy1, xy2 : (float, float)
Points for the line to pass through.
Either *xy2* or *slope* has to be given.
slope : float, optional
The slope of the line. Either *xy2* or *slope* has to be given.

Returns
-------
Expand All @@ -941,12 +950,29 @@ def axline(self, xy1, xy2, **kwargs):

>>> axline((0, 0), (1, 1), linewidth=4, color='r')
"""
def _to_points(xy1, xy2, slope):
"""
Check for a valid combination of input parameters and convert
to two points, if necessary.
"""
if (xy2 is None and slope is None or
xy2 is not None and slope is not None):
raise TypeError(
"Exactly one of 'xy2' and 'slope' must be given")
if xy2 is None:
x1, y1 = xy1
xy2 = (x1, y1 + 1) if np.isinf(slope) else (x1 + 1, y1 + slope)
return xy1, xy2

if "transform" in kwargs:
raise TypeError("'transform' is not allowed as a kwarg; "
"axline generates its own transform")
x1, y1 = xy1
x2, y2 = xy2
if slope is not None and (self.get_xscale() != 'linear' or
self.get_yscale() != 'linear'):
raise TypeError("'slope' cannot be used with non-linear scales")

datalim = [xy1] if xy2 is None else [xy1, xy2]
(x1, y1), (x2, y2) = _to_points(xy1, xy2, slope)
line = mlines._AxLine([x1, x2], [y1, y2], **kwargs)
# Like add_line, but correctly handling data limits.
self._set_artist_props(line)
Expand All @@ -956,7 +982,7 @@ def axline(self, xy1, xy2, **kwargs):
line.set_label(f"_line{len(self.lines)}")
self.lines.append(line)
line._remove_method = self.lines.remove
self.update_datalim([xy1, xy2])
self.update_datalim(datalim)

self._request_autoscale_view()
return line
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4 changes: 2 additions & 2 deletions lib/matplotlib/pyplot.py
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Expand Up @@ -2290,8 +2290,8 @@ def axis(*args, emit=True, **kwargs):

# Autogenerated by boilerplate.py. Do not edit as changes will be lost.
@_copy_docstring_and_deprecators(Axes.axline)
def axline(xy1, xy2, **kwargs):
return gca().axline(xy1, xy2, **kwargs)
def axline(xy1, xy2=None, *, slope=None, **kwargs):
return gca().axline(xy1, xy2=xy2, slope=slope, **kwargs)


# Autogenerated by boilerplate.py. Do not edit as changes will be lost.
Expand Down
24 changes: 24 additions & 0 deletions lib/matplotlib/tests/test_axes.py
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Expand Up @@ -3929,12 +3929,36 @@ def test_axline(fig_test, fig_ref):
ax.axline((0, 0), (1, 1))
ax.axline((0, 0), (1, 0), color='C1')
ax.axline((0, 0.5), (1, 0.5), color='C2')
# slopes
ax.axline((-0.7, -0.5), slope=0, color='C3')
ax.axline((1, -0.5), slope=-0.5, color='C4')
ax.axline((-0.5, 1), slope=float('inf'), color='C5')

ax = fig_ref.subplots()
ax.set(xlim=(-1, 1), ylim=(-1, 1))
ax.plot([-1, 1], [-1, 1])
ax.axhline(0, color='C1')
ax.axhline(0.5, color='C2')
# slopes
ax.axhline(-0.5, color='C3')
ax.plot([-1, 1], [0.5, -0.5], color='C4')
ax.axvline(-0.5, color='C5')


def test_axline_args():
"""Exactly one of *xy2* and *slope* must be specified."""
fig, ax = plt.subplots()
with pytest.raises(TypeError):
ax.axline((0, 0)) # missing second parameter
with pytest.raises(TypeError):
ax.axline((0, 0), (1, 1), slope=1) # redundant parameters
ax.set_xscale('log')
with pytest.raises(TypeError):
ax.axline((0, 0), slope=1)
ax.set_xscale('linear')
ax.set_yscale('log')
with pytest.raises(TypeError):
ax.axline((0, 0), slope=1)


@image_comparison(['vlines_basic', 'vlines_with_nan', 'vlines_masked'],
Expand Down