add clear() method

CHANGES

@@ -5,6 +5,8 @@ Changelog
 Version 0.8 (in development)
 ----------------------------
 
+Add clear()-method for Graph and Digraph. 
+
 Add grapviz.version() function.
 
 Drop dot source extra indent for edge statements following dotguide examples.

docs/api.rst

@@ -18,7 +18,7 @@ Graph
         source,
         node, edge, edges, attr, subgraph,
         format, engine, encoding,
-        copy, pipe, save, render, view
+        clear, copy, pipe, save, render, view
 
 
 Digraph
@@ -29,7 +29,7 @@ Digraph
         source,
         node, edge, edges, attr, subgraph,
         format, engine, encoding,
-        copy, pipe, save, render, view
+        clear, copy, pipe, save, render, view
 
 
 Source

graphviz/dot.py

@@ -79,6 +79,17 @@ def _kwargs(self):
         })
         return result
 
+    def clear(self, keep_attrs=False):
+        """Reset content to an empty body, clear graph/node/egde_attr mappings.
+
+        Args:
+            keep_attrs(bool): preserve graph/node/egde_attr mappings
+        """
+        if not keep_attrs:
+            for a in (self.graph_attr, self.node_attr, self.edge_attr):
+                a.clear()
+        self.body[:] = []
+
     def __iter__(self, subgraph=False):
         """Yield the DOT source code line by line (as graph or subgraph)."""
         if self.comment:

tests/test_dot.py

@@ -39,6 +39,24 @@ def test__repr_svg_(mocker, cls):
     pipe.return_value.decode.assert_called_once_with(c.encoding)
 
 
+@pytest.mark.parametrize('keep_attrs', [False, True])
+def test_clear(cls, keep_attrs):
+    kwargs = {'%s_attr' % a: {a: a} for a in ('graph', 'node', 'edge')}
+    c = cls(**kwargs)
+    assert all(getattr(c, k) == v for k, v in kwargs.items())
+    c.node('spam')
+    assert len(c.body) == 1
+    body = c.body
+
+    c.clear(keep_attrs)
+    assert c.body == []
+    assert c.body is body
+    if keep_attrs:
+        assert all(getattr(c, k) == v for k, v in kwargs.items())
+    else:
+        assert all(getattr(c, k) == {} for k, v in kwargs.items())
+
+
 def test_iter_subgraph_strict(cls):
     with pytest.raises(ValueError, match=r'strict'):
         cls().subgraph(cls(strict=True))