def create(self, prog=None, format='ps', encoding=None):
        """Creates and returns a binary image for the graph.

        create will write the graph to a temporary dot file in the
        encoding specified by `encoding` and process it with the
        program given by 'prog' (which defaults to 'twopi'), reading
        the binary image output and return it as:

        - `str` of bytes in Python 2
        - `bytes` in Python 3

        There's also the preferred possibility of using:

            create_'format'(prog='program')

        which are automatically defined for all the supported formats,
        for example:

          - `create_ps()`
          - `create_gif()`
          - `create_dia()`

        If 'prog' is a list, instead of a string,
        then the fist item is expected to be the program name,
        followed by any optional command-line arguments for it:

            [ 'twopi', '-Tdot', '-s10' ]


        @param prog: either:

          - name of GraphViz executable that
            can be found in the `$PATH`, or

          - absolute path to GraphViz executable.

          If you have added GraphViz to the `$PATH` and
          use its executables as installed
          (without renaming any of them)
          then their names are:

            - `'dot'`
            - `'twopi'`
            - `'neato'`
            - `'circo'`
            - `'fdp'`
            - `'sfdp'`

          On Windows, these have the notorious ".exe" extension that,
          only for the above strings, will be added automatically.

          The `$PATH` is inherited from `os.env['PATH']` and
          passed to `subprocess.Popen` using the `env` argument.

          If you haven't added GraphViz to your `$PATH` on Windows,
          then you may want to give the absolute path to the
          executable (for example, to `dot.exe`) in `prog`.
        """

        if prog is None:
            prog = self.prog

        assert prog is not None

        if isinstance(prog, (list, tuple)):
            prog, args = prog[0], prog[1:]
        else:
            args = []

        # temp file
        tmp_fd, tmp_name = tempfile.mkstemp()
        os.close(tmp_fd)
        self.write(tmp_name, encoding=encoding)
        tmp_dir = os.path.dirname(tmp_name)

        # For each of the image files...
        for img in self.shape_files:
            # Get its data
            f = open(img, 'rb')
            f_data = f.read()
            f.close()
            # And copy it under a file with the same name in
            # the temporary directory
            f = open(os.path.join(tmp_dir, os.path.basename(img)), 'wb')
            f.write(f_data)
            f.close()

        arguments = ['-T{}'.format(format), ] + args + [tmp_name]

        try:
            stdout_data, stderr_data, process = call_graphviz(
                program=prog,
                arguments=arguments,
                working_dir=tmp_dir,
            )
        except OSError as e:
            if e.errno == errno.ENOENT:
                args = list(e.args)
                args[1] = '"{prog}" not found in path.'.format(
                    prog=prog)
                raise OSError(*args)
            else:
                raise

        # clean file litter
        for img in self.shape_files:
            os.unlink(os.path.join(tmp_dir, os.path.basename(img)))

        os.unlink(tmp_name)

        if process.returncode != 0:
            message = (
                '"{prog}" with args {arguments} returned code: {code}\n\n'
                'stdout, stderr:\n {out}\n{err}\n'
            ).format(
                prog=prog,
                arguments=arguments,
                code=process.returncode,
                out=stdout_data,
                err=stderr_data,
            )
            print(message)

        assert process.returncode == 0, process.returncode

        return stdout_data
Creates and returns a binary image for the graph.

        create will write the graph to a temporary dot file in the
        encoding specified by `encoding` and process it with the
        program given by 'prog' (which defaults to 'twopi'), reading
        the binary image output and return it as:

        - `str` of bytes in Python 2
        - `bytes` in Python 3

        There's also the preferred possibility of using:

            create_'format'(prog='program')

        which are automatically defined for all the supported formats,
        for example:

          - `create_ps()`
          - `create_gif()`
          - `create_dia()`

        If 'prog' is a list, instead of a string,
        then the fist item is expected to be the program name,
        followed by any optional command-line arguments for it:

            [ 'twopi', '-Tdot', '-s10' ]


        @param prog: either:

          - name of GraphViz executable that
            can be found in the `$PATH`, or

          - absolute path to GraphViz executable.

          If you have added GraphViz to the `$PATH` and
          use its executables as installed
          (without renaming any of them)
          then their names are:

            - `'dot'`
            - `'twopi'`
            - `'neato'`
            - `'circo'`
            - `'fdp'`
            - `'sfdp'`

          On Windows, these have the notorious ".exe" extension that,
          only for the above strings, will be added automatically.

          The `$PATH` is inherited from `os.env['PATH']` and
          passed to `subprocess.Popen` using the `env` argument.

          If you haven't added GraphViz to your `$PATH` on Windows,
          then you may want to give the absolute path to the
          executable (for example, to `dot.exe`) in `prog`.