Source: yt Followup-For: Bug #810209 Looking into it (with my limited pyhton knowledge), I think it is using matplot lib for its png need:
File yt/utilities/png_writer.py: (...) import matplotlib._png as _png (...) if MPL_VERSION < MPL_API_2_VERSION: def call_png_write_png(buffer, width, height, filename, dpi): _png.write_png(buffer, width, height, filename, dpi) else: def call_png_write_png(buffer, width, height, filename, dpi): _png.write_png(buffer, filename, dpi) -- System Information: Debian Release: stretch/sid APT prefers unstable APT policy: (500, 'unstable'), (500, 'testing') Architecture: amd64 (x86_64) Foreign Architectures: i386 Kernel: Linux 4.3.0-1-amd64 (SMP w/4 CPU cores) Locale: LANG=de_DE.UTF-8, LC_CTYPE=de_DE.UTF-8 (charmap=UTF-8) Shell: /bin/sh linked to /bin/dash Init: systemd (via /run/systemd/system)