dot_parser: Define parser elements in a class (#464)

ferdnyc · web-flow · commit 7dd60c367c0a · 2025-04-05T13:02:27.000+02:00
* core: Import dot_parser on demand

* dot_parser: Move parser definition into class

Instead of a global variable `graphparser` that's set by calling
a function the first time it's referenced, set up the parser
definition in a class `GraphParser`, so that it can be accessed
as `GraphParser.parser`.

This has the advantage that all of its _component_ parts (like
the definition of `subgraph_stmt`, or `attr_list` can also
be accessed as `GraphParser.subgraph_stmt` or
`GraphParser.attr_list`, etc. (Much better for debugging/testing.)

In addition, to improve dependency relationships:
- Only import pydot.core into dot_parser, not `pydot`
- Change all `pydot.Foo` references to `pydot.core.Foo`
- Use concrete `pydot.core.Foo`s in type annotations
  (instead of strings)

* Remove unused args from parse actions

* parser: Remove unnecessary type-ignore from HTML.__init__

It annoyed mypy in strict mode.

* dot_parser: Define 'graphparser' at module level

Strictly for compatibility, in case anyone is using it directly.
They probably shouldn't be, but this way we won't break their code.

* Move low-end MyPy check to Python 3.9
diff --git a/setup.cfg b/setup.cfg
@@ -61,5 +61,5 @@ python =
     3.12 = py312
     3.11 = py311
     3.10 = py310
-    3.9 = py39
-    3.8 = mypy-check, py38
+    3.9 = mypy-check, py39
+    3.8 = py38
diff --git a/src/pydot/core.py b/src/pydot/core.py
@@ -15,7 +15,6 @@
 from typing import Any, List, Optional, Sequence, Set, Tuple, Type, Union, cast
 
 import pydot
-import pydot.dot_parser
 from pydot._vendor import tempfile
 from pydot.classes import AttributeDict, FrozenDict
 
@@ -401,6 +400,8 @@ def graph_from_dot_data(s: str) -> Optional[List["Dot"]]:
     @return: Graphs that result from parsing.
     @rtype: `list` of `pydot.Dot`
     """
+    import pydot.dot_parser
+
     return pydot.dot_parser.parse_dot_data(s)
 
 
diff --git a/src/pydot/dot_parser.py b/src/pydot/dot_parser.py
