move default encoding definition to backend, re-order engine, format,…

… encoding

graphviz/backend.py

@@ -78,6 +78,8 @@
 
 FORMATTERS = {'cairo', 'core', 'gd', 'gdiplus', 'gdwbmp', 'xlib'}
 
+ENCODING = 'utf-8'
+
 PLATFORM = platform.system().lower()
 
 
@@ -249,7 +251,7 @@ def pipe(engine, format, data, renderer=None, formatter=None, quiet=False):
 
 def unflatten(source,
               stagger=None, fanout=False, chain=None,
-              encoding='utf-8'):
+              encoding=ENCODING):
     """Return DOT ``source`` piped through Graphviz *unflatten* preprocessor.
 
     Args:

graphviz/dot.py

@@ -28,8 +28,9 @@
 'test-output/m00se.gv.pdf'
 """
 
-from . import lang
+from . import backend
 from . import files
+from . import lang
 
 __all__ = ['Graph', 'Digraph']
 
@@ -52,7 +53,7 @@ class Dot(files.File):
 
     def __init__(self, name=None, comment=None,
                  filename=None, directory=None,
-                 format=None, engine=None, encoding=files.ENCODING,
+                 format=None, engine=None, encoding=backend.ENCODING,
                  graph_attr=None, node_attr=None, edge_attr=None, body=None,
                  strict=False):
         self.name = name

graphviz/files.py

@@ -15,29 +15,17 @@
 
 __all__ = ['File', 'Source']
 
-ENCODING = 'utf-8'
-
 
 log = logging.getLogger(__name__)
 
 
 class Base(object):
 
-    _format = 'pdf'
     _engine = 'dot'
-    _encoding = ENCODING
 
-    @property
-    def format(self):
-        """The output format used for rendering (``'pdf'``, ``'png'``, ...)."""
-        return self._format
+    _format = 'pdf'
 
-    @format.setter
-    def format(self, format):
-        format = format.lower()
-        if format not in backend.FORMATS:
-            raise ValueError('unknown format: %r' % format)
-        self._format = format
+    _encoding = backend.ENCODING
 
     @property
     def engine(self):
@@ -51,6 +39,18 @@ def engine(self, engine):
             raise ValueError('unknown engine: %r' % engine)
         self._engine = engine
 
+    @property
+    def format(self):
+        """The output format used for rendering (``'pdf'``, ``'png'``, ...)."""
+        return self._format
+
+    @format.setter
+    def format(self, format):
+        format = format.lower()
+        if format not in backend.FORMATS:
+            raise ValueError('unknown format: %r' % format)
+        self._format = format
+
     @property
     def encoding(self):
         """The encoding for the saved source file."""
@@ -85,7 +85,7 @@ class File(Base):
     _default_extension = 'gv'
 
     def __init__(self, filename=None, directory=None,
-                 format=None, engine=None, encoding=ENCODING):
+                 format=None, engine=None, encoding=backend.ENCODING):
         if filename is None:
             name = getattr(self, 'name', None) or self.__class__.__name__
             filename = '%s.%s' % (name, self._default_extension)
@@ -323,7 +323,7 @@ class Source(File):
 
     @classmethod
     def from_file(cls, filename, directory=None,
-                  format=None, engine=None, encoding=ENCODING):
+                  format=None, engine=None, encoding=backend.ENCODING):
         """Return an instance with the source string read from the given file.
 
         Args:
@@ -342,7 +342,7 @@ def from_file(cls, filename, directory=None,
         return cls(source, filename, directory, format, engine, encoding)
 
     def __init__(self, source, filename=None, directory=None,
-                 format=None, engine=None, encoding=ENCODING):
+                 format=None, engine=None, encoding=backend.ENCODING):
         super(Source, self).__init__(filename, directory,
                                      format, engine, encoding)
         self.source = source  #: The verbatim DOT source code string.

tests/test_files.py

@@ -19,14 +19,6 @@ def source():
     return Source(**SOURCE)
 
 
-def test_format(source):
-    assert not SOURCE['format'].islower()
-
-    assert source.format == SOURCE['format'].lower()
-    with pytest.raises(ValueError, match=r'format'):
-        source.format = ''
-
-
 def test_engine(source):
     assert not SOURCE['engine'].islower()
 
@@ -35,6 +27,14 @@ def test_engine(source):
         source.engine = ''
 
 
+def test_format(source):
+    assert not SOURCE['format'].islower()
+
+    assert source.format == SOURCE['format'].lower()
+    with pytest.raises(ValueError, match=r'format'):
+        source.format = ''
+
+
 def test_encoding(source):
     assert source.encoding == SOURCE['encoding']