8000 matplotlib plots not showing when using "ipython --pylab" · Issue #14401 · ipython/ipython · GitHub
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alaniwi opened this issue Apr 12, 2024 · 3 comments · Fixed by #14403
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matplotlib plots not showing when using "ipython --pylab" #14401

alaniwi opened this issue Apr 12, 2024 · 3 comments · Fixed by #14403

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@alaniwi
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alaniwi commented Apr 12, 2024

In versions of ipython up to 8.21.0, when invoked with ipython --pylab, matplotlib plots are displayed to the screen automatically, and without blocking. In later versions (8.22.* and 8.23.0), they are not, and can only be displayed using plt.show(block=True).

Here are steps to reproduce. This uses pip installation on Ubuntu for a simple example (where /usr/bin/python3 is python 3.10.12), although I have also observed the issue in conda environments on both Ubuntu and CentOS, based on python 3.11 and 3.12.

1) Working example -- with ipython 8.21.0:

$  python3 -m venv /tmp/myenv
$  . /tmp/myenv/bin/activate
(myenv) $  pip install pyqt5 numpy matplotlib ipython==8.21.0
(myenv) $  ipython --pylab
In [1]:  plt.plot(np.arange(10)**2)

A plot appears on the screen automatically (without needing to call plt.show explicitly) -- and in non-blocking mode, so you can continue to type at the ipython In [2]: prompt.

Screenshot of plot window

2) Broken example with ipython 8.23.0:

  • use the same commands as above, except ipython==8.23.0

In this case, a matplotlib window is opened, but it is black (with no plot).

Screenshot of plot window

If plt.show() or plt.show(block=False) is typed, neither of these succeed in displaying the plot -- and if plt.show(block=False) is typed then not long afterwards a message from GNOME appears saying "matplotlib is not responding". The plot is only shown if plt.show(block=True) is typed, in which case, it blocks as requested (so no futher prompt is issued until the plot is closed).

In these examples, matplotlib was version 3.8.4, although further experimentation shows that it does not seem to depend on the matplotlib version.

Please can you restore the behaviour that is obtained in earlier versions.
@ianthomas23
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This might be due to #14330. I will investigate.

@ianthomas23
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@alaniwi Thanks for reporting this, it is definitely a bug that I introduced in #14330.

The problem occurs using ipython --pylab or ipython --pylab=auto (the former is shorthand for the latter). But if you specify a GUI event loop then it works, so the workaround in your situation is to use ipython --pylab=qt.

I have a fix, which will be in the next release.

@ianthomas23 ianthomas23 mentioned this issue Apr 13, 2024
Merged
Carreau added a commit that referenced this issue Apr 15, 2024
@Carreau
Fix use of --pylab=auto and --matplotlib=auto (#14403)
3b57430 
Fixes #14401 which has been a bug in the 8.22.x and 8.23.x releases.

When I removed the multiple initialisation of Matplotlib backends in
#14330 it broke use of the following:
```bash
ipython --matplotlib
ipython --matplotlib=auto
ipython --pylab
ipython --pylab=auto
```
by failing to display Matplotlib plot. If you specify a particular GUI
event loop such as using
```bash
ipython --pylab=qt
```
then it was and is fine. So for anyone finding this, the workaround
until the next release is to specify a GUI loop rather than relying on
the auto selection.

I didn't notice this as I've been concentrating on moving the Matplotlib
backend logic from IPython to Matplotlib, and with those changes
(matplotlib/matplotlib#27948) the above use cases all work OK.

The fix is to reintroduce the early import of `matplotlib-inline` but
only if both the gui loop is not specified and the Matplotlib version is
before the movement of the backend logic across to it.

There are no explicit tests for this. In the future I will try to think
of some tests for some of this IPython-Matplotlib functionality that
don't involve installing complicated backend dependencies or adding
image comparison tests.
@alaniwi
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alaniwi commented Apr 15, 2024

Great, thank you for the quick response.

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Fix use of --pylab=auto and --matplotlib=auto ianthomas23/ipython
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@ianthomas23 @alaniwi
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