imshow bug on GTKCairo and GTK3Cairo

[OceanWolf]

On master, the following code fails (works fine on master with GTK3Agg and with GTK3Cairo on 1.3.1 (debian))

import matplotlib
matplotlib.use('GTK3Cairo')
import matplotlib.pyplot as plt
import numpy as np

data = np.linspace(0, 10, 80).reshape(10, 8)

plt.imshow(data)
plt.show()

File "matplotlib/lib/matplotlib/backends/backend_cairo.py", line 169, in in draw_image
    buf, cairo.FORMAT_ARGB32, cols, rows, cols*4)
TypeError: Cannot use string as modifiable buffer

[tacaswell]

python 2 or 3? My guess is that this is related to the str -> (byte, unicode) conversion + conversion using six.

[OceanWolf]

python2.7, using python-cairo version 1.8.8 on both mpl-1.3.1 and master.

[OceanWolf]

Ooh, debian has just upped, to mpl-1.4.2 on debian-testing...

Just tested on 1.4.2 (which uses six) and I don't see the problem, but the upgrade has also upgraded a few other things as well, and borked my access to my testing directory of python, so I shall try and fix that tomorrow and test again and come back with some news.

[OceanWolf]

Okay, tested it again and I still see it on master, fine using 1.4.2, bad on master, both using python 1.7.8 and python-cairo version 1.8.8.

[OceanWolf]

Okay, some poking in the code:

mpl_version	print(type(buf))
1.4.2	<type 'buffer'>
master	<type 'str'>

I will try and follow the code back further, to see why this happens.

[OceanWolf]

Okay, my skills run dead as this looks like a bug in the c to python code _image. I have no idea about that layer of code.

[tacaswell]

This is probably related to the major cxx removal refactor then attn @mdboom

[mdboom]

Try #4163.

[OceanWolf]

I can't seem to pull this, I have weak git-foo...

git fetch upstream pull/4154/head:pr4154
fatal: Couldn't find remote ref pull/4154/head

[mdboom]

Use 4163. 4154 is just an issue (with no code attached).

[tacaswell]

Closed by 2a028c0