dtlib: clean up DT initialization

Initialize all the public API interface related attributes within the
constructor instead of scattering them throughout the implementation
of the class, and make sure they all have type annotations.

Move all the parsing code away from the init routines and public API
down to the main parsing block.

This is for readability and paves the way for later changes that
affect the way initialization happens.

Signed-off-by: Martí Bolívar <marti.bolivar@nordicsemi.no>

scripts/dts/python-devicetree/src/devicetree/dtlib.py

@@ -21,7 +21,7 @@ import string
 import sys
 import textwrap
 from typing import Any, Dict, Iterable, List, \
-    NamedTuple, NoReturn, Optional, Tuple, Union
+    NamedTuple, NoReturn, Optional, Set, Tuple, Union
 
 # NOTE: tests/test_dtlib.py is the test suite for this library.
 
@@ -734,32 +734,18 @@ class DT:
           Try not to raise DTError even if the input tree has errors.
           For experimental use; results not guaranteed.
         """
+        self._root: Optional[Node] = None
+        self.alias2node: Dict[str, Node] = {}
+        self.label2node: Dict[str, Node] = {}
+        self.label2prop: Dict[str, Property] = {}
+        self.label2prop_offset: Dict[str, Tuple[Property, int]] = {}
+        self.phandle2node: Dict[int, Node] = {}
+        self.memreserves: List[Tuple[Set[str], int, int]] = []
         self.filename = filename
-        self._include_path = list(include_path)
+
         self._force = force
 
-        with open(filename, encoding="utf-8") as f:
-            self._file_contents = f.read()
-
-        self._tok_i = self._tok_end_i = 0
-        self._filestack: List[_FileStackElt] = []
-
-        self.alias2node: Dict[str, Node] = {}
-
-        self._lexer_state: int = _DEFAULT
-        self._saved_token: Optional[_Token] = None
-
-        self._lineno: int = 1
-
-        self._root: Optional[Node] = None
-
-        self._parse_dt()
-
-        self._register_phandles()
-        self._fixup_props()
-        self._register_aliases()
-        self._remove_unreferenced()
-        self._register_labels()
+        self._parse_file(filename, include_path)
 
     @property
     def root(self) -> Node:
@@ -853,13 +839,37 @@ class DT:
         Returns some information about the DT instance. Called automatically if
         the DT instance is evaluated.
         """
-        return f"DT(filename='{self.filename}', " \
-            f"include_path={self._include_path})"
+        if self.filename:
+            return f"DT(filename='{self.filename}', " \
+                f"include_path={self._include_path})"
+        return super().__repr__()
 
     #
     # Parsing
     #
 
+    def _parse_file(self, filename, include_path):
+        self._include_path = list(include_path)
+
+        with open(filename, encoding="utf-8") as f:
+            self._file_contents = f.read()
+
+        self._tok_i = self._tok_end_i = 0
+        self._filestack: List[_FileStackElt] = []
+
+        self._lexer_state: int = _DEFAULT
+        self._saved_token: Optional[_Token] = None
+
+        self._lineno: int = 1
+
+        self._parse_dt()
+
+        self._register_phandles()
+        self._fixup_props()
+        self._register_aliases()
+        self._remove_unreferenced()
+        self._register_labels()
+
     def _parse_dt(self):
         # Top-level parsing loop
 
@@ -932,7 +942,6 @@ class DT:
     def _parse_memreserves(self):
         # Parses /memreserve/, which appears after /dts-v1/
 
-        self.memreserves = []
         while True:
             # Labels before /memreserve/
             labels = []
@@ -1580,7 +1589,6 @@ class DT:
         # that set. Also checks the format of the phandles and does misc.
         # sanity checking.
 
-        self.phandle2node = {}
         for node in self.node_iter():
             phandle = node.props.get("phandle")
             if phandle:
@@ -1722,10 +1730,6 @@ class DT:
 
         label2things = collections.defaultdict(set)
 
-        self.label2node = {}
-        self.label2prop = {}
-        self.label2prop_offset = {}
-
         # Register all labels and the nodes/props they point to in label2things
         for node in self.node_iter():
             for label in node.labels: