[Matplotlib-users] Replacing deprecated use of pyplot.subplot

[Paul Hobson]

Errr, make that last line:

h_mpl = bode_plot(h, ax_mag=g_mpl['axes'][0], ax_phase=g_mpl['axes']*[1]*)

On Sat, Jan 20, 2018 at 1:02 PM, Paul Hobson <pmhobson at gmail.com> wrote:

> Hey Rory,
>
> In general, especially for library code, you should avoid relying on the
> pyplot state machine.
>
> That means explicitly passing Axes and Figure object around to and from
> your functions.
>
> For me, making that switch meant added an `ax=None` kwarg to the end of my
> function signatures.
>
> Then I carry around an axes_validator function that looks something like
> this:
> https://github.com/matplotlib/mpl-probscale/blob/master/
> probscale/validate.py#L6
>
> But that's not really necessary. So in your case, I think you should do
> something like this:
>
>
> import numpy as np
> import matplotlib.pyplot as plt
>
>
> def bode_plot(g, ax_mag=None, ax_phase=None, mag_opts=None,
> phase_opts=None):
>     # create axes if they're not both supplied
>     if not ax_mag or not ax_phase:
>         fig, (ax_mag, ax_phase) = plt.subplots(nrows=2)
>
>     # make the plotting options empty dicts if
>     # not supplied
>     if not mag_opts:
>         mag_opts = {}
>
>     if not phase_opts:
>         phase_opts = {}
>
>     # compute signal stuff
>     freq, mag, phase = freq_resp(g)
>
>     # 99% sure semilogx returns a tuple of artists, so I unpack it
>     # you should check this though
>     mag_artist, = ax_mag.semilogx(freq, 20 * np.log10(mag), **mag_opts)
>     phase_artist, = ax_phase.semilogx(freq, phase, **phase_opts)
>
>     # package the output for later (if you want to modify artists)
>     output = {
>         'fig': fig,
>         'axes': (ax_mag, ax_phase),
>         'arists': (mag_artist, phase_artist)
>     }
>     return output
>
> And then you'd use the code like this:
>
> fig, (ax_mag, ax_phase) = plt.subplots(nrows=2, figsize=(12, 6))
> g_mpl = bode_plot(g, ax_mag=ax_mag, ax_phase=ax_phase, color='r',
> linewidth=2, label='G')
> h_mpl = bode_plot(h, ax_mag=ax_mag, ax_phase=ax_phase, color='b'm
> linewidth=1, label='H')
> ax_mag.legend()
>
>
> Or do something like this:
> g_mpl = bode_plot(g, color='r', linewidth=2, label='G')
> h_mpl = bode_plot(h, ax_mag=g_mpl['axes'][0], ax_phase=g_mpl['axes'][0])
>
>
> Does that help?
> -Paul
>
>
> On Sat, Jan 20, 2018 at 11:44 AM, Rory Yorke <rory.yorke at gmail.com> wrote:
>
>> Hi,
>>
>> I'm a contributor to the Python Control Systems Library [1], which uses
>> Matplotlib for plotting.
>>
>> We recently noticed deprecation warnings due to how we use
>> pyplot.subplot.  We use it in the Matlab manner of either getting a
>> handle to an existing axis, or creating one if no suitable axis exists.
>>
>> The warning is
>>
>>   MatplotlibDeprecationWarning: Adding an axes using the same arguments
>>   as a previous axes currently reuses the earlier instance.  In a future
>>   version, a new instance will always be created and returned.
>>   Meanwhile, this warning can be suppressed, and the future behavior
>>   ensured, by passing a unique label to each axes instance.
>>
>> For example, to plot the frequency response a linear dynamical system
>> (AKA Bode plot of the system), the relevant function could be simplified
>> to:
>>
>>     def bode_plot(g):
>>        freq, mag, phase = freq_resp(g)
>>        subplot(211)
>>        semilogx(freq, 20*log10(mag))
>>        subplot(212)
>>        semilogx(freq, phase)
>>
>> We've replaced that with code like this:
>>
>>     def bode_plot(g):
>>        freq, mag, phase = freq_resp(g)
>>
>>        ax_mag = None
>>        ax_phase = None
>>        for ax in gcf.axes():
>>            if ax.get_label() == 'control-bode-magnitude':
>>              ax_mag = ax
>>            elif ax.get_label() == 'control-bode-phase':
>>              ax_phase = ax
>>
>>        if ax_mag is None or ax_phase is None:
>>          clf()
>>          ax_mag = subplot(211, label = 'control-bode-magnitude')
>>          ax_phase = subplot(212, label = 'control-bode-phase)
>>
>>        ax_mag.semilogx(freq, 20*log10(mag))
>>        ax_phase.semilogx(freq, phase)
>>
>> This means that calls like
>>
>>     bode_plot(g)
>>     bode_plot(h)
>>
>> will show the response of g and h on the same figure.
>>
>> Is this method of using labels to check for existing axes reasonable?
>> Is there a better way?
>>
>> Actual code exhibiting warnings at [2]; new code at [3].  The latter
>> link is to an as-yet unmerged branch, and may disappear.
>>
>> Thanks,
>>
>> Rory
>>
>> [1] https://github.com/python-control/python-control
>> [2] https://github.com/python-control/python-control/blob/af8d4e
>> e39dfa574c2b3b335f4cdb4be858ae469a/control/freqplot.py#L175
>> [3] https://github.com/murrayrm/python-control/blob/dc1820a4e64d
>> 73937c7de8df078c41ec1773e048/control/freqplot.py#L138
>> _______________________________________________
>> Matplotlib-users mailing list
>> Matplotlib-users at python.org
>> https://mail.python.org/mailman/listinfo/matplotlib-users
>>
>
>
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