Bug summary

On Linux with fontconfig 2.17 (released in June 2025) installed, a warning is printed when making plots:

Fontconfig warning: using without calling FcInit()

Code for reproduction

>>> import matplotlib.pyplot as plt
>>> plt.plot([1, 2, 3], [4, 5, 6])
Fontconfig warning: using without calling FcInit()
[<matplotlib.lines.Line2D object at 0x7fa81cb0f4d0>]
>>>

Actual outcome

Warning is printed to stderr:

Fontconfig warning: using without calling FcInit()

Expected outcome

no warning printed

Additional information

This closed issue on fontconfig's issue tracker suggests that downstream projects using fontconfig ought to make some change (presumably: calling a function named FcInit()) to avoid this.

It sounds like fontconfig does what's needed (for the time being) such that there's no actual behavioural issue, so I think any change right now would just be to suppress the warning.

Operating system

Arch Linux

Matplotlib Version

3.10.3

Matplotlib Backend

qtagg

Python version

3.13.5

Jupyter version

No response

Installation

Linux package manager