Add fallback decoding for STEP file loading

profiling/p21_loader.py

@@ -52,7 +52,7 @@ def load_p21(fn: Path) -> LoadResult:
     start_time = time.perf_counter()
     loaded = time.perf_counter()
     try:
-        data = open(str(fn), mode='rt', encoding=p21.STEP_FILE_ENCODING).read()
+        data = open(str(fn), mode='rt', encoding=p21.STEP_FILE_ENCODINGS).read()
         loaded = time.perf_counter()
         content = p21.loads(data)
     except IOError as e:

src/steputils/p21.py

@@ -46,7 +46,7 @@
 
 # ISO 10303-21-2016 allows UTF-8 encoding, prior versions of the standard used used IOS-8859-1 encoding, but
 # lower code points (<127) are the same for both encodings.
-STEP_FILE_ENCODING = "utf-8"
+STEP_FILE_ENCODINGS = ("utf-8", "latin-1", "cp1252")
 END_OF_INSTANCE = ";\n"
 
 BACKSLASH = "\\"
@@ -513,7 +513,7 @@ def _set_schemas(self):
 
     def save(self, name: str) -> None:
         """Export STEP-file to the file system."""
-        with open(name, mode="wt", encoding=STEP_FILE_ENCODING) as fp:
+        with open(name, mode="wt", encoding=STEP_FILE_ENCODINGS) as fp:
             self.write(fp)
 
     def __str__(self) -> str:
@@ -1161,5 +1161,14 @@ def load(fp: TextIO) -> StepFile:
 
 def readfile(filename: str) -> StepFile:
     """Read STEP-file (ISO 10303-21:2002) `filename` from file system."""
-    with open(filename, "rt", encoding=STEP_FILE_ENCODING) as fp:
-        return load(fp)
+
+    last_error = None
+
+    for encoding in STEP_FILE_ENCODINGS:
+        try:
+            with open(filename, "rt", encoding=encoding) as fp:
+                return load(fp)
+        except UnicodeDecodeError as exc:
+            last_error = exc
+
+    raise last_error