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ENH: add secondary x/y axis
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‎.flake8

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@@ -228,6 +228,7 @@ per-file-ignores =
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examples/subplots_axes_and_figures/axes_zoom_effect.py: E402
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examples/subplots_axes_and_figures/demo_constrained_layout.py: E402
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examples/subplots_axes_and_figures/demo_tight_layout.py: E402
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examples/subplots_axes_and_figures/secondary_axis.py: E402
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examples/subplots_axes_and_figures/two_scales.py: E402
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examples/subplots_axes_and_figures/zoom_inset_axes.py: E402
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examples/tests/backend_driver_sgskip.py: E402, E501

‎doc/api/axes_api.rst

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@@ -188,6 +188,8 @@ Text and Annotations
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Axes.inset_axes
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Axes.indicate_inset
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Axes.indicate_inset_zoom
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Axes.secondary_xaxis
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Axes.secondary_yaxis
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Fields

‎doc/users/next_whats_new/2018-09-08-JMK.rst

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:orphan:
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Secondary x/y Axis support
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--------------------------
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A new method provides the ability to add a second axis to an existing
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axes via `.Axes.secondary_xaxis` and `.Axes.secondary_yaxis`. See
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:doc:`/gallery/subplots_axes_and_figures/secondary_axis` for examples.
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.. plot::
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import matplotlib.pyplot as plt
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fig, ax = plt.subplots(figsize=(5, 3))
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ax.plot(range(360))
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ax.secondary_xaxis('top', functions=(np.deg2rad, np.rad2deg))

‎examples/subplots_axes_and_figures/secondary_axis.py

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"""
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==============
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Secondary Axis
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==============
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Sometimes we want as secondary axis on a plot, for instance to convert
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radians to degrees on the same plot. We can do this by making a child
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axes with only one axis visible via `.Axes.axes.secondary_xaxis` and
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`.Axes.axes.secondary_yaxis`.
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If we want to label the top of the axes:
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"""
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import matplotlib.pyplot as plt
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import numpy as np
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import datetime
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import matplotlib.dates as mdates
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from matplotlib.transforms import Transform
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from matplotlib.ticker import (
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AutoLocator, AutoMinorLocator)
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fig, ax = plt.subplots(constrained_layout=True)
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x = np.arange(0, 360, 1)
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y = np.sin(2 * x * np.pi / 180)
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ax.plot(x, y)
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ax.set_xlabel('angle [degrees]')
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ax.set_ylabel('signal')
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ax.set_title('Sine wave')
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secax = ax.secondary_xaxis('top')
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plt.show()
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###########################################################################
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# However, its often useful to label the secondary axis with something
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# other than the labels in the main axis. In that case we need to provide
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# both a forward and an inverse conversion function in a tuple
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# to the ``functions`` kwarg:
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fig, ax = plt.subplots(constrained_layout=True)
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x = np.arange(0, 360, 1)
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y = np.sin(2 * x * np.pi / 180)
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ax.plot(x, y)
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ax.set_xlabel('angle [degrees]')
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ax.set_ylabel('signal')
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ax.set_title('Sine wave')
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def deg2rad(x):
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return x * np.pi / 180
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def rad2deg(x):
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return x * 180 / np.pi
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secax = ax.secondary_xaxis('top', functions=(deg2rad, rad2deg))
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secax.set_xlabel('angle [rad]')
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plt.show()
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###########################################################################
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# Here is the case of converting from wavenumber to wavelength in a
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# log-log scale.
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#
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# .. note ::
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#
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# In this case, the xscale of the parent is logarithmic, so the child is
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# made logarithmic as well.
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fig, ax = plt.subplots(constrained_layout=True)
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x = np.arange(0.02, 1, 0.02)
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np.random.seed(19680801)
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y = np.random.randn(len(x)) ** 2
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ax.loglog(x, y)
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ax.set_xlabel('f [Hz]')
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ax.set_ylabel('PSD')
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ax.set_title('Random spectrum')
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def forward(x):
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return 1 / x
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def inverse(x):
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return 1 / x
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secax = ax.secondary_xaxis('top', functions=(forward, inverse))
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secax.set_xlabel('period [s]')
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plt.show()
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###########################################################################
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# Sometime we want to relate the axes in a transform that is ad-hoc from
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# the data, and is derived empirically. In that case we can set the
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# forward and inverse transforms functions to be linear interpolations from the
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# one data set to the other.
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fig, ax = plt.subplots(constrained_layout=True)
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xdata = np.arange(1, 11, 0.4)
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ydata = np.random.randn(len(xdata))
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ax.plot(xdata, ydata, label='Plotted data')
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xold = np.arange(0, 11, 0.2)
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# fake data set relating x co-ordinate to another data-derived co-ordinate.
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xnew = np.sort(10 * np.exp(-xold / 4) + np.random.randn(len(xold)) / 3)
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ax.plot(xold[3:], xnew[3:], label='Transform data')
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ax.set_xlabel('X [m]')
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ax.legend()
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def forward(x):
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return np.interp(x, xold, xnew)
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def inverse(x):
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return np.interp(x, xnew, xold)
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secax = ax.secondary_xaxis('top', functions=(forward, inverse))
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secax.xaxis.set_minor_locator(AutoMinorLocator())
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secax.set_xlabel('$X_{other}$')
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plt.show()
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###########################################################################
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# A final example translates np.datetime64 to yearday on the x axis and
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# from Celsius to Farenheit on the y axis:
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dates = [datetime.datetime(2018, 1, 1) + datetime.timedelta(hours=k * 6)
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for k in range(240)]
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temperature = np.random.randn(len(dates))
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fig, ax = plt.subplots(constrained_layout=True)
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ax.plot(dates, temperature)
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ax.set_ylabel(r'$T\ [^oC]$')
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plt.xticks(rotation=70)
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def date2yday(x):
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"""
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x is in matplotlib datenums, so they are floats.
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"""
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y = x - mdates.date2num(datetime.datetime(2018, 1, 1))
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return y
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def yday2date(x):
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"""
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return a matplotlib datenum (x is days since start of year)
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"""
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y = x + mdates.date2num(datetime.datetime(2018, 1, 1))
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return y
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secaxx = ax.secondary_xaxis('top', functions=(date2yday, yday2date))
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secaxx.set_xlabel('yday [2018]')
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def CtoF(x):
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return x * 1.8 + 32
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def FtoC(x):
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return (x - 32) / 1.8
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secaxy = ax.secondary_yaxis('right', functions=(CtoF, FtoC))
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secaxy.set_ylabel(r'$T\ [^oF]$')
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plt.show()
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#############################################################################
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#
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# ------------
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#
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# References
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# """"""""""
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#
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# The use of the following functions and methods is shown in this example:
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import matplotlib
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matplotlib.axes.Axes.secondary_xaxis
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matplotlib.axes.Axes.secondary_yaxis

‎lib/matplotlib/_constrained_layout.py

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@@ -180,7 +180,8 @@ def do_constrained_layout(fig, renderer, h_pad, w_pad,
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sup = fig._suptitle
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bbox = invTransFig(sup.get_window_extent(renderer=renderer))
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height = bbox.y1 - bbox.y0
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sup._layoutbox.edit_height(height+h_pad)
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if np.isfinite(height):
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sup._layoutbox.edit_height(height+h_pad)
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# OK, the above lines up ax._poslayoutbox with ax._layoutbox
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# now we need to
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"""
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fig = ax.figure
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invTransFig = fig.transFigure.inverted().transform_bbox
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pos = ax.get_position(original=True)
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tightbbox = ax.get_tightbbox(renderer=renderer)
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bbox = invTransFig(tightbbox)
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# this can go wrong:
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if not np.isfinite(bbox.y0 + bbox.x0 + bbox.y1 + bbox.x1):
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# just abort, this is likely a bad set of co-ordinates that
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# is transitory...
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return
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# use stored h_pad if it exists
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h_padt = ax._poslayoutbox.h_pad
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if h_padt is None:
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_log.debug('left %f', (-bbox.x0 + pos.x0 + w_pad))
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_log.debug('right %f', (bbox.x1 - pos.x1 + w_pad))
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_log.debug('bottom %f', (-bbox.y0 + pos.y0 + h_padt))
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_log.debug('bbox.y0 %f', bbox.y0)
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_log.debug('pos.y0 %f', pos.y0)
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# Sometimes its possible for the solver to collapse
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# rather than expand axes, so they all have zero height
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# or width. This stops that... It *should* have been

‎lib/matplotlib/axes/_axes.py

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import matplotlib.tri as mtri
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from matplotlib.container import BarContainer, ErrorbarContainer, StemContainer
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from matplotlib.axes._base import _AxesBase, _process_plot_format
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from matplotlib.axes._secondary_axes import SecondaryAxis
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_log = logging.getLogger(__name__)
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600601
return rectpatch, connects
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@docstring.dedent_interpd
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def secondary_xaxis(self, location, *, functions=None, **kwargs):
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"""
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Add a second x-axis to this axes.
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For example if we want to have a second scale for the data plotted on
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the xaxis.
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%(_secax_docstring)s
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Examples
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--------
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Add a secondary axes that shows both wavelength for the main
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axes that shows wavenumber.
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.. plot::
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fig, ax = plt.subplots()
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ax.loglog(range(1, 360, 5), range(1, 360, 5))
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ax.set_xlabel('frequency [Hz]')
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def invert(x):
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return 1 / x
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secax = ax.secondary_xaxis('top', functions=(invert, invert))
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secax.set_xlabel('Period [s]')
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plt.show()
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"""
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if (location in ['top', 'bottom'] or isinstance(location, Number)):
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secondary_ax = SecondaryAxis(self, 'x', location, functions,
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**kwargs)
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self.add_child_axes(secondary_ax)
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return secondary_ax
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else:
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raise ValueError('secondary_xaxis location must be either '
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'a float or "top"/"bottom"')
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def secondary_yaxis(self, location, *, functions=None, **kwargs):
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"""
646+
Add a second y-axis to this axes.
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For example if we want to have a second scale for the data plotted on
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the yaxis.
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%(_secax_docstring)s
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Examples
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--------
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Add a secondary axes that converts from radians to degrees
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.. plot::
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fig, ax = plt.subplots()
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ax.plot(range(1, 360, 5), range(1, 360, 5))
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ax.set_ylabel('degrees')
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secax = ax.secondary_yaxis('right', functions=(np.deg2rad,
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np.rad2deg))
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secax.set_ylabel('radians')
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"""
668+
if location in ['left', 'right'] or isinstance(location, Number):
669+
secondary_ax = SecondaryAxis(self, 'y', location,
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functions, **kwargs)
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self.add_child_axes(secondary_ax)
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return secondary_ax
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else:
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raise ValueError('secondary_yaxis location must be either '
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'a float or "left"/"right"')
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def text(self, x, y, s, fontdict=None, withdash=False, **kwargs):
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"""
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Add text to the axes.

‎lib/matplotlib/axes/_base.py

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@@ -2500,8 +2500,17 @@ def _update_title_position(self, renderer):
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title.set_position((x, 1.0))
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# need to check all our twins too...
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axs = self._twinned_axes.get_siblings(self)
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top = 0 # the top of all the axes twinned with this axes...
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# and all the children
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for ax in self.child_axes:
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if ax is not None:
2506+
locator = ax.get_axes_locator()
2507+
if locator:
2508+
pos = locator(self, renderer)
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ax.apply_aspect(pos)
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else:
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ax.apply_aspect()
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axs = axs + [ax]
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top = 0
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for ax in axs:
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try:
25072516
if (ax.xaxis.get_label_position() == 'top'
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# prevent triggering call backs during the draw process
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self._stale = True
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# loop over self and child axes...
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locator = self.get_axes_locator()
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if locator:
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pos = locator(self, renderer)
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43154326
if bb_yaxis:
43164327
bb.append(bb_yaxis)
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4329+
self._update_title_position(renderer)
4330+
bb.append(self.get_window_extent(renderer))
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43184332
self._update_title_position(renderer)
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if self.title.get_visible():
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bb.append(self.title.get_window_extent(renderer))

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