Further improve exception traceback readability

src/PIL/ImImagePlugin.py

@@ -201,9 +201,8 @@ class ImImageFile(ImageFile.ImageFile):
 
             else:
 
-                raise SyntaxError(
+                msg = "Syntax error in IM header: " + s.decode("ascii", "replace")
-                    "Syntax error in IM header: " + s.decode("ascii", "replace")
+                raise SyntaxError(msg)
-                )
 
         if not n:
             msg = "Not an IM file"

src/PIL/Image.py

@@ -2129,7 +2129,7 @@ class Image:
             Resampling.BOX,
             Resampling.HAMMING,
         ):
-            message = f"Unknown resampling filter ({resample})."
+            msg = f"Unknown resampling filter ({resample})."
 
             filters = [
                 f"{filter[1]} ({filter[0]})"
@@ -2142,9 +2142,8 @@ class Image:
                     (Resampling.HAMMING, "Image.Resampling.HAMMING"),
                 )
             ]
-            raise ValueError(
+            msg += " Use " + ", ".join(filters[:-1]) + " or " + filters[-1]
-                message + " Use " + ", ".join(filters[:-1]) + " or " + filters[-1]
+            raise ValueError(msg)
-            )
 
         if reducing_gap is not None and reducing_gap < 1.0:
             msg = "reducing_gap must be 1.0 or greater"
@@ -2764,13 +2763,13 @@ class Image:
             Resampling.BICUBIC,
         ):
             if resample in (Resampling.BOX, Resampling.HAMMING, Resampling.LANCZOS):
-                message = {
+                msg = {
                     Resampling.BOX: "Image.Resampling.BOX",
                     Resampling.HAMMING: "Image.Resampling.HAMMING",
                     Resampling.LANCZOS: "Image.Resampling.LANCZOS",
                 }[resample] + f" ({resample}) cannot be used."
             else:
-                message = f"Unknown resampling filter ({resample})."
+                msg = f"Unknown resampling filter ({resample})."
 
             filters = [
                 f"{filter[1]} ({filter[0]})"
@@ -2780,9 +2779,8 @@ class Image:
                     (Resampling.BICUBIC, "Image.Resampling.BICUBIC"),
                 )
             ]
-            raise ValueError(
+            msg += " Use " + ", ".join(filters[:-1]) + " or " + filters[-1]
-                message + " Use " + ", ".join(filters[:-1]) + " or " + filters[-1]
+            raise ValueError(msg)
-            )
 
         image.load()
 
@@ -3077,7 +3075,8 @@ def fromarray(obj, mode=None):
         try:
             mode, rawmode = _fromarray_typemap[typekey]
         except KeyError as e:
-            raise TypeError("Cannot handle this data type: %s, %s" % typekey) from e
+            msg = "Cannot handle this data type: %s, %s" % typekey
+            raise TypeError(msg) from e
     else:
         rawmode = mode
     if mode in ["1", "L", "I", "P", "F"]:
@@ -3276,9 +3275,8 @@ def open(fp, mode="r", formats=None):
         fp.close()
     for message in accept_warnings:
         warnings.warn(message)
-    raise UnidentifiedImageError(
+    msg = "cannot identify image file %r" % (filename if filename else fp)
-        "cannot identify image file %r" % (filename if filename else fp)
+    raise UnidentifiedImageError(msg)
-    )
 
 
 #

src/PIL/ImageCms.py

@@ -498,7 +498,8 @@ def buildTransform(
         raise PyCMSError(msg)
 
     if not isinstance(flags, int) or not (0 <= flags <= _MAX_FLAG):
-        raise PyCMSError("flags must be an integer between 0 and %s" + _MAX_FLAG)
+        msg = "flags must be an integer between 0 and %s" + _MAX_FLAG
+        raise PyCMSError(msg)
 
     try:
         if not isinstance(inputProfile, ImageCmsProfile):
@@ -601,7 +602,8 @@ def buildProofTransform(
         raise PyCMSError(msg)
 
     if not isinstance(flags, int) or not (0 <= flags <= _MAX_FLAG):
-        raise PyCMSError("flags must be an integer between 0 and %s" + _MAX_FLAG)
+        msg = "flags must be an integer between 0 and %s" + _MAX_FLAG
+        raise PyCMSError(msg)
 
     try:
         if not isinstance(inputProfile, ImageCmsProfile):

src/PIL/ImageFile.py

@@ -63,12 +63,13 @@ Dict of known error codes returned from :meth:`.PyDecoder.decode`,
 
 def raise_oserror(error):
     try:
-        message = Image.core.getcodecstatus(error)
+        msg = Image.core.getcodecstatus(error)
     except AttributeError:
-        message = ERRORS.get(error)
+        msg = ERRORS.get(error)
-    if not message:
+    if not msg:
-        message = f"decoder error {error}"
+        msg = f"decoder error {error}"
-    raise OSError(message + " when reading image file")
+    msg += " when reading image file"
+    raise OSError(msg)
 
 
 def _tilesort(t):

src/PIL/ImageMorph.py

@@ -146,7 +146,8 @@ class LutBuilder:
         for p in self.patterns:
             m = re.search(r"(\w*):?\s*\((.+?)\)\s*->\s*(\d)", p.replace("\n", ""))
             if not m:
-                raise Exception('Syntax error in pattern "' + p + '"')
+                msg = 'Syntax error in pattern "' + p + '"'
+                raise Exception(msg)
             options = m.group(1)
             pattern = m.group(2)
             result = int(m.group(3))

src/PIL/PdfParser.py

@@ -817,10 +817,10 @@ class PdfParser:
                 try:
                     stream_len = int(result[b"Length"])
                 except (TypeError, KeyError, ValueError) as e:
-                    raise PdfFormatError(
+                    msg = "bad or missing Length in stream dict (%r)" % result.get(
-                        "bad or missing Length in stream dict (%r)"
+                        b"Length", None
-                        % result.get(b"Length", None)
+                    )
-                    ) from e
+                    raise PdfFormatError(msg) from e
                 stream_data = data[m.end() : m.end() + stream_len]
                 m = cls.re_stream_end.match(data, m.end() + stream_len)
                 check_format_condition(m, "stream end not found")
@@ -874,7 +874,8 @@ class PdfParser:
         if m:
             return cls.get_literal_string(data, m.end())
         # return None, offset  # fallback (only for debugging)
-        raise PdfFormatError("unrecognized object: " + repr(data[offset : offset + 32]))
+        msg = "unrecognized object: " + repr(data[offset : offset + 32])
+        raise PdfFormatError(msg)
 
     re_lit_str_token = re.compile(
         rb"(\\[nrtbf()\\])|(\\[0-9]{1,3})|(\\(\r\n|\r|\n))|(\r\n|\r|\n)|(\()|(\))"

winbuild/build_prepare.py

@@ -491,7 +491,8 @@ def extract_dep(url, filename):
                     raise RuntimeError(msg)
             tgz.extractall(sources_dir)
     else:
-        raise RuntimeError("Unknown archive type: " + filename)
+        msg = "Unknown archive type: " + filename
+        raise RuntimeError(msg)
 
 
 def write_script(name, lines):
@@ -628,7 +629,8 @@ if __name__ == "__main__":
         elif arg == "--srcdir":
             sources_dir = os.path.sep + "src"
         else:
-            raise ValueError("Unknown parameter: " + arg)
+            msg = "Unknown parameter: " + arg
+            raise ValueError(msg)
 
     # dependency cache directory
     os.makedirs(depends_dir, exist_ok=True)