Error, when using matplotlib in a python script embedded in a C++ program

Question

I have a python script which is invoked inside a C++ application. When I import matplotlib I get the following error.

List index out of range.

In my script the only matplotlibrelated code is

import matplotlib.pyplot as plt
f = plt.figure()

When I invoke the script on its own it works. I get this exception only when it is embedded in a C++ Program. Do I need to provide some extra dependencies when the script uses matplotlib?

When I comment out the matplotlibfunctions I don't get the exception

Update

The C++ Code is from the python docs link : 1.3. Pure Embedding

I haven't modified anything from the C++ code. It works as long as there are no matplotlib related code.

can you provide a minimal reproducible example ?

463035818_is_not_an_ai
– 463035818_is_not_an_ai

2019-12-10 09:42:34 +00:00
Commented Dec 10, 2019 at 9:42 — 463035818_is_not_an_ai
– 463035818_is_not_an_ai, Commented Dec 10, 2019 at 9:42
how do you embed it in c++?

463035818_is_not_an_ai
– 463035818_is_not_an_ai

2019-12-10 09:43:09 +00:00
Commented Dec 10, 2019 at 9:43 — 463035818_is_not_an_ai
– 463035818_is_not_an_ai, Commented Dec 10, 2019 at 9:43
updated the post.

abhilb
– abhilb

2019-12-10 09:45:33 +00:00
Commented Dec 10, 2019 at 9:45 — abhilb
– abhilb, Commented Dec 10, 2019 at 9:45
1.3 Pure Embedding I have mentioned that in the post.

abhilb
– abhilb

2019-12-10 09:47:46 +00:00
Commented Dec 10, 2019 at 9:47 — abhilb
– abhilb, Commented Dec 10, 2019 at 9:47

abhilb · Accepted Answer · 2019-12-10 10:08:15Z

1

The reason is that the backend used by matplotlib is tk in my case. The window initialization of the tk has this code in there

baseName = os.path.basename(sys.argv[0])

And in my case the argv is empty and that is the reason for list index out of range error.

One work around I found here. We can passing dummy values like this:

    wchar_t const *dummy_args[] = { L"Python", NULL };  // const is needed because literals must not be modified
    wchar_t const **argv = dummy_args;
    int             argc = sizeof(dummy_args) / sizeof(dummy_args[0]) - 1;
    PySys_SetArgv(argc, const_cast<wchar_t **>(argv));

answered Dec 10, 2019 at 10:08

abhilb

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