issue with display hook in base python repl

This only applies to the base python repl, everything works in IPython repls.

In discussion on b2fbae7 discovered that sys.displayhook only gets evaluated for expressions, not statements.

This means that things like

import numpy
pass
a = b

will not trigger the auto-redrawing. This is particularly troubling because this mean

ln, = ax.plot(...)

will not trigger a re-draw, but

ax.plot(...)

will.

Due to b2fbae7, where we rely on the auto-redrawing to trigger the pyplot redrawing this means that many pyplot workflows in the normal repl are broken (as in things that used to auto-redraw no longer do).

The options I think are:

figure out how to trigger a call back on statements (if this is possible, it is well hidden. There may be a reason IPython completely re-wrote the execution handling)
say we only support interactive plotting with the IPython repl (which is a major regression)
revert the removal of draw_if_interactive which maintains some functions as 'special'

I suspect that the answer is going to be both 2 and 3. normal python shell keeps current functionality and gains some new functionality, IPython picks up lots of new functionality, and the code base keeps this particular wart.

MNT : remove draw_if_interactive from boilerplate

Another option may be to hook draw_if_interactive into the callback stack on Figure objects to queue up a draw when the figure becomes stale.

copied from commit thread:

If we tie this to the state change of stale on the Figure, it will only get flipped to True once so there should only be one call to draw_if_interactive/draw_idle anyway.

My current inclination is to change the repl registration to use the IPython hooks if they are available and the Figure-based callback otherwise.

I will take a crack at this tomorrow morning.

ENH: redraw callback on Figure in base repl

Something I just noticed when playing around with the interactive mode in python REPL. If I create a figure and then call plt.ion(), the subsequent plotting call (which happens to be an expression) does not trigger a show(). Nothing shows until I do plt.show().

>>> import matplotlib.pyplot as plt
>>> fig, ax = plt.subplots()
>>> ax.plot([1, 2, 3])
[<matplotlib.lines.Line2D object at 0x7fc82dbd9c90>]
>>> plt.ion()    # I now decide I want to see what I am doing
>>> ax.plot([3, 2, 1])  # No figure window!
[<matplotlib.lines.Line2D object at 0x7fc82d4a0f90>]
>>> ax.set_xlabel('x data')  # Still no figure window!
<matplotlib.text.Text object at 0x7fc83f0c15d0>
>>> plt.show()  # Figure window appears
>>> fig, ax = plt.subplots()  # New figure window appears right away and subsequent plotting calls work immediately

Sure, but that's expected behaviour right? The same happens with python -i not switching to interactive mode until the script has finished executing...

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issue with display hook in base python repl #4504

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issue with display hook in base python repl #4504

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tacaswell commented on Jun 8, 2015

tacaswell commented on Jun 8, 2015

WeatherGod commented on Jun 25, 2015

OceanWolf commented on Jul 14, 2015

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