I need to execute shell command in python program (I have ubuntu). More specifically I want to create graph using graphviz in python script. My code is

os.system("dot -Tpng graph.dot -o graph.png")

It does not work, but if I just type dot -Tpng graph.dot -o graph.png in command line then everything is fine. Do you know what the problem? Thank you!

Edit: Does not work means that nothing happens, there are no errors.

Output from dot -v -Tpng graph.dot -o graph.png:

dot - graphviz version 2.26.3 (20100126.1600)

Activated plugin library: libgvplugin_pango.so.6

Using textlayout: textlayout:cairo

Activated plugin library: libgvplugin_dot_layout.so.6

Using layout: dot:dot_layout

Using render: cairo:cairo

Using device: png:cairo:cairo

The plugin configuration file:

    /usr/lib/graphviz/config6

        was successfully loaded.

    render  :  cairo dot fig gd map ps svg tk vml vrml xdot

    layout  :  circo dot fdp neato nop nop1 nop2 osage patchwork sfdp twopi

    textlayout  :  textlayout

    device  :  canon cmap cmapx cmapx_np dot eps fig gd gd2 gif gv imap         imap_np ismap jpe jpeg jpg pdf plain plain-ext png ps ps2 svg svgz tk vml vmlz vrml wbmp x11 xdot xlib

    loadimage   :  (lib) eps gd gd2 gif jpe jpeg jpg png ps svg