Python 3.4 Windows byte decoding error in agraph.py

[aleksihakli]

Python 3.4 causes a byte decoding error on Windows due to agraph.py Warnings being raised from a joined bytes object instead of a normal str object which has unicode encoding.

The versions of software in use are:

Windows 10 Version 1511 64-bit
Python 3.4.4 32-bit
Graphviz 2.38 32-bit
pygraphviz 1.3.1 32-bit build from http://www.lfd.uci.edu/~gohlke/pythonlibs/
django_extensions 1.6.7

When running graph_models command which uses pygraphviz for graph generation with the django_extensions package the error is as following:

$ ./manage.py graph_models -a -g -o my_project_visualized.png
Traceback (most recent call last):
  File "./manage.py", line 10, in <module>
    execute_from_command_line(sys.argv)
  File "C:\Users\me\project\virtualenv32\lib\site-packages\django\core\management\__init__.py", line 354, in execute_from_command_line
    utility.execute()
  File "C:\Users\me\project\virtualenv32\lib\site-packages\django\core\management\__init__.py", line 346, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "C:\Users\me\project\virtualenv32\lib\site-packages\django\core\management\base.py", line 394, in run_from_argv
    self.execute(*args, **cmd_options)
  File "C:\Users\me\project\virtualenv32\lib\site-packages\django\core\management\base.py", line 445, in execute
    output = self.handle(*args, **options)
  File "C:\Users\me\project\virtualenv32\lib\site-packages\django_extensions\management\utils.py", line 58, in inner
    ret = func(self, *args, **kwargs)
  File "C:\Users\me\project\virtualenv32\lib\site-packages\django_extensions\management\commands\graph_models.py", line 162, in handle
    self.render_output_pygraphviz(dotdata, **options)
  File "C:\Users\me\project\virtualenv32\lib\site-packages\django_extensions\management\commands\graph_models.py", line 202, in render_output_pygraphviz
    graph.layout(prog=kwargs['layout'])
  File "C:\Users\me\project\virtualenv32\lib\site-packages\pygraphviz\agraph.py", line 1358, in layout
    data = self._run_prog(prog, ' '.join([args, "-T", fmt]))
  File "C:\Users\me\project\virtualenv32\lib\site-packages\pygraphviz\agraph.py", line 1338, in _run_prog
    warnings.warn(b"".join(errors), RuntimeWarning)
TypeError: can't use a string pattern on a bytes-like object

The excepted output depicting font warnings would be on Windows:

WARNING:py.warnings:C:\Users\me\project\virtualenv32\lib\site-packages\pygraphviz\agraph.py:1338: RuntimeWarning:
(neato.exe:30444): Pango-WARNING **: couldn't load font "Helvetica Bold Not-Rotated 8", falling back to "Sans Bold Not-Rotated 8", expect ugly output.

(neato.exe:30444): Pango-WARNING **: couldn't load font "Helvetica Italic Not-Rotated 8", falling back to "Sans Italic Not-Rotated 8", expect ugly output.

(neato.exe:30444): Pango-WARNING **: couldn't load font "Helvetica Not-Rotated 8", falling back to "Sans Not-Rotated 8", expect ugly output.

(neato.exe:30444): Pango-WARNING **: couldn't load font "Helvetica ItalicBold Not-Rotated 8", falling back to "Sans Not-Rotated 8", expect ugly output.

(neato.exe:30444): Pango-WARNING **: couldn't load font "Helvetica Bold Not-Rotated 12", falling back to "Sans Bold Not-Rotated 12", expect ugly output.

  warnings.warn(b"".join(errors).decode(), RuntimeWarning)

The crashing segment of code from agraph.py line 1339 is:

        if not data:
            raise IOError(b"".join(errors))

        if len(errors) > 0:
            warnings.warn(b"".join(errors), RuntimeWarning)

After making the following fix the program runs normally on my local machine on Python 3 32-bit, 64-bit, and Python 2.7 64-bit:

        if not data:
            raise IOError(b"".join(errors).decode())

        if len(errors) > 0:
            warnings.warn(b"".join(errors).decode(), RuntimeWarning)

I am proposing that to support Python 3 graph generation a bytes decoding is added to the error-causing code segment in

[hagberg]

Fixed in #95