Fix exception causes all over the codebase

docs/example/DdsImagePlugin.py

@@ -249,8 +249,8 @@ class DXT1Decoder(ImageFile.PyDecoder):
     def decode(self, buffer):
         try:
             self.set_as_raw(_dxt1(self.fd, self.state.xsize, self.state.ysize))
-        except struct.error:
+        except struct.error as e:
-            raise OSError("Truncated DDS file")
+            raise OSError("Truncated DDS file") from e
         return 0, 0
 
 
@@ -260,8 +260,8 @@ class DXT5Decoder(ImageFile.PyDecoder):
     def decode(self, buffer):
         try:
             self.set_as_raw(_dxt5(self.fd, self.state.xsize, self.state.ysize))
-        except struct.error:
+        except struct.error as e:
-            raise OSError("Truncated DDS file")
+            raise OSError("Truncated DDS file") from e
         return 0, 0
 
 

src/PIL/BlpImagePlugin.py

@@ -282,8 +282,8 @@ class _BLPBaseDecoder(ImageFile.PyDecoder):
             self.magic = self.fd.read(4)
             self._read_blp_header()
             self._load()
-        except struct.error:
+        except struct.error as e:
-            raise OSError("Truncated Blp file")
+            raise OSError("Truncated Blp file") from e
         return 0, 0
 
     def _read_palette(self):

src/PIL/BmpImagePlugin.py

@@ -304,8 +304,8 @@ def _dib_save(im, fp, filename):
 def _save(im, fp, filename, bitmap_header=True):
     try:
         rawmode, bits, colors = SAVE[im.mode]
-    except KeyError:
+    except KeyError as e:
-        raise OSError("cannot write mode %s as BMP" % im.mode)
+        raise OSError("cannot write mode %s as BMP" % im.mode) from e
 
     info = im.encoderinfo
 

src/PIL/EpsImagePlugin.py

@@ -231,8 +231,8 @@ class EpsImageFile(ImageFile.ImageFile):
 
                 try:
                     m = split.match(s)
-                except re.error:
+                except re.error as e:
-                    raise SyntaxError("not an EPS file")
+                    raise SyntaxError("not an EPS file") from e
 
                 if m:
                     k, v = m.group(1, 2)

src/PIL/FpxImagePlugin.py

@@ -59,8 +59,8 @@ class FpxImageFile(ImageFile.ImageFile):
 
         try:
             self.ole = olefile.OleFileIO(self.fp)
-        except OSError:
+        except OSError as e:
-            raise SyntaxError("not an FPX file; invalid OLE file")
+            raise SyntaxError("not an FPX file; invalid OLE file") from e
 
         if self.ole.root.clsid != "56616700-C154-11CE-8553-00AA00A1F95B":
             raise SyntaxError("not an FPX file; bad root CLSID")

src/PIL/GdImageFile.py

@@ -81,5 +81,5 @@ def open(fp, mode="r"):
 
     try:
         return GdImageFile(fp)
-    except SyntaxError:
+    except SyntaxError as e:
-        raise UnidentifiedImageError("cannot identify this image file")
+        raise UnidentifiedImageError("cannot identify this image file") from e

src/PIL/GifImagePlugin.py

@@ -130,9 +130,9 @@ class GifImageFile(ImageFile.ImageFile):
         for f in range(self.__frame + 1, frame + 1):
             try:
                 self._seek(f)
-            except EOFError:
+            except EOFError as e:
                 self.seek(last_frame)
-                raise EOFError("no more images in GIF file")
+                raise EOFError("no more images in GIF file") from e
 
     def _seek(self, frame):
 

src/PIL/ImImagePlugin.py

@@ -163,8 +163,8 @@ class ImImageFile(ImageFile.ImageFile):
 
             try:
                 m = split.match(s)
-            except re.error:
+            except re.error as e:
-                raise SyntaxError("not an IM file")
+                raise SyntaxError("not an IM file") from e
 
             if m:
 
@@ -341,8 +341,8 @@ def _save(im, fp, filename):
 
     try:
         image_type, rawmode = SAVE[im.mode]
-    except KeyError:
+    except KeyError as e:
-        raise ValueError("Cannot save %s images as IM" % im.mode)
+        raise ValueError("Cannot save %s images as IM" % im.mode) from e
 
     frames = im.encoderinfo.get("frames", 1)
 

src/PIL/Image.py

@@ -434,8 +434,8 @@ def _getdecoder(mode, decoder_name, args, extra=()):
     try:
         # get decoder
         decoder = getattr(core, decoder_name + "_decoder")
-    except AttributeError:
+    except AttributeError as e:
-        raise OSError("decoder %s not available" % decoder_name)
+        raise OSError("decoder %s not available" % decoder_name) from e
     return decoder(mode, *args + extra)
 
 
@@ -457,8 +457,8 @@ def _getencoder(mode, encoder_name, args, extra=()):
     try:
         # get encoder
         encoder = getattr(core, encoder_name + "_encoder")
-    except AttributeError:
+    except AttributeError as e:
-        raise OSError("encoder %s not available" % encoder_name)
+        raise OSError("encoder %s not available" % encoder_name) from e
     return encoder(mode, *args + extra)
 
 
@@ -971,10 +971,10 @@ class Image:
                         if isinstance(t, tuple):
                             try:
                                 t = trns_im.palette.getcolor(t)
-                            except Exception:
+                            except Exception as e:
                                 raise ValueError(
                                     "Couldn't allocate a palette color for transparency"
-                                )
+                                ) from e
                     trns_im.putpixel((0, 0), t)
 
                     if mode in ("L", "RGB"):
@@ -1027,8 +1027,8 @@ class Image:
                 # normalize source image and try again
                 im = self.im.convert(getmodebase(self.mode))
                 im = im.convert(mode, dither)
-            except KeyError:
+            except KeyError as e:
-                raise ValueError("illegal conversion")
+                raise ValueError("illegal conversion") from e
 
         new_im = self._new(im)
         if delete_trns:
@@ -1625,16 +1625,16 @@ class Image:
                 mode = getmodebase(self.mode) + "A"
                 try:
                     self.im.setmode(mode)
-                except (AttributeError, ValueError):
+                except (AttributeError, ValueError) as e:
                     # do things the hard way
                     im = self.im.convert(mode)
                     if im.mode not in ("LA", "PA", "RGBA"):
-                        raise ValueError  # sanity check
+                        raise ValueError from e  # sanity check
                     self.im = im
                 self.pyaccess = None
                 self.mode = self.im.mode
-            except (KeyError, ValueError):
+            except (KeyError, ValueError) as e:
-                raise ValueError("illegal image mode")
+                raise ValueError("illegal image mode") from e
 
         if self.mode in ("LA", "PA"):
             band = 1
@@ -2136,8 +2136,8 @@ class Image:
                 init()
             try:
                 format = EXTENSION[ext]
-            except KeyError:
+            except KeyError as e:
-                raise ValueError("unknown file extension: {}".format(ext))
+                raise ValueError("unknown file extension: {}".format(ext)) from e
 
         if format.upper() not in SAVE:
             init()
@@ -2238,8 +2238,8 @@ class Image:
         if isinstance(channel, str):
             try:
                 channel = self.getbands().index(channel)
-            except ValueError:
+            except ValueError as e:
-                raise ValueError('The image has no channel "{}"'.format(channel))
+                raise ValueError('The image has no channel "{}"'.format(channel)) from e
 
         return self._new(self.im.getband(channel))
 
@@ -2736,12 +2736,12 @@ def fromarray(obj, mode=None):
     if mode is None:
         try:
             typekey = (1, 1) + shape[2:], arr["typestr"]
-        except KeyError:
+        except KeyError as e:
-            raise TypeError("Cannot handle this data type")
+            raise TypeError("Cannot handle this data type") from e
         try:
             mode, rawmode = _fromarray_typemap[typekey]
-        except KeyError:
+        except KeyError as e:
-            raise TypeError("Cannot handle this data type: %s, %s" % typekey)
+            raise TypeError("Cannot handle this data type: %s, %s" % typekey) from e
     else:
         rawmode = mode
     if mode in ["1", "L", "I", "P", "F"]:

src/PIL/ImageCms.py

@@ -369,7 +369,7 @@ def profileToProfile(
         else:
             imOut = transform.apply(im)
     except (OSError, TypeError, ValueError) as v:
-        raise PyCMSError(v)
+        raise PyCMSError(v) from v
 
     return imOut
 
@@ -393,7 +393,7 @@ def getOpenProfile(profileFilename):
     try:
         return ImageCmsProfile(profileFilename)
     except (OSError, TypeError, ValueError) as v:
-        raise PyCMSError(v)
+        raise PyCMSError(v) from v
 
 
 def buildTransform(
@@ -474,7 +474,7 @@ def buildTransform(
             inputProfile, outputProfile, inMode, outMode, renderingIntent, flags=flags
         )
     except (OSError, TypeError, ValueError) as v:
-        raise PyCMSError(v)
+        raise PyCMSError(v) from v
 
 
 def buildProofTransform(
@@ -585,7 +585,7 @@ def buildProofTransform(
             flags,
         )
     except (OSError, TypeError, ValueError) as v:
-        raise PyCMSError(v)
+        raise PyCMSError(v) from v
 
 
 buildTransformFromOpenProfiles = buildTransform
@@ -640,7 +640,7 @@ def applyTransform(im, transform, inPlace=False):
         else:
             imOut = transform.apply(im)
     except (TypeError, ValueError) as v:
-        raise PyCMSError(v)
+        raise PyCMSError(v) from v
 
     return imOut
 
@@ -682,15 +682,15 @@ def createProfile(colorSpace, colorTemp=-1):
     if colorSpace == "LAB":
         try:
             colorTemp = float(colorTemp)
-        except (TypeError, ValueError):
+        except (TypeError, ValueError) as e:
             raise PyCMSError(
                 'Color temperature must be numeric, "%s" not valid' % colorTemp
-            )
+            ) from e
 
     try:
         return core.createProfile(colorSpace, colorTemp)
     except (TypeError, ValueError) as v:
-        raise PyCMSError(v)
+        raise PyCMSError(v) from v
 
 
 def getProfileName(profile):
@@ -732,7 +732,7 @@ def getProfileName(profile):
         return "{} - {}\n".format(model, manufacturer)
 
     except (AttributeError, OSError, TypeError, ValueError) as v:
-        raise PyCMSError(v)
+        raise PyCMSError(v) from v
 
 
 def getProfileInfo(profile):
@@ -772,7 +772,7 @@ def getProfileInfo(profile):
         return "\r\n\r\n".join(arr) + "\r\n\r\n"
 
     except (AttributeError, OSError, TypeError, ValueError) as v:
-        raise PyCMSError(v)
+        raise PyCMSError(v) from v
 
 
 def getProfileCopyright(profile):
@@ -800,7 +800,7 @@ def getProfileCopyright(profile):
             profile = ImageCmsProfile(profile)
         return (profile.profile.copyright or "") + "\n"
     except (AttributeError, OSError, TypeError, ValueError) as v:
-        raise PyCMSError(v)
+        raise PyCMSError(v) from v
 
 
 def getProfileManufacturer(profile):
@@ -828,7 +828,7 @@ def getProfileManufacturer(profile):
             profile = ImageCmsProfile(profile)
         return (profile.profile.manufacturer or "") + "\n"
     except (AttributeError, OSError, TypeError, ValueError) as v:
-        raise PyCMSError(v)
+        raise PyCMSError(v) from v
 
 
 def getProfileModel(profile):
@@ -857,7 +857,7 @@ def getProfileModel(profile):
             profile = ImageCmsProfile(profile)
         return (profile.profile.model or "") + "\n"
     except (AttributeError, OSError, TypeError, ValueError) as v:
-        raise PyCMSError(v)
+        raise PyCMSError(v) from v
 
 
 def getProfileDescription(profile):
@@ -886,7 +886,7 @@ def getProfileDescription(profile):
             profile = ImageCmsProfile(profile)
         return (profile.profile.profile_description or "") + "\n"
     except (AttributeError, OSError, TypeError, ValueError) as v:
-        raise PyCMSError(v)
+        raise PyCMSError(v) from v
 
 
 def getDefaultIntent(profile):
@@ -925,7 +925,7 @@ def getDefaultIntent(profile):
             profile = ImageCmsProfile(profile)
         return profile.profile.rendering_intent
     except (AttributeError, OSError, TypeError, ValueError) as v:
-        raise PyCMSError(v)
+        raise PyCMSError(v) from v
 
 
 def isIntentSupported(profile, intent, direction):
@@ -976,7 +976,7 @@ def isIntentSupported(profile, intent, direction):
         else:
             return -1
     except (AttributeError, OSError, TypeError, ValueError) as v:
-        raise PyCMSError(v)
+        raise PyCMSError(v) from v
 
 
 def versions():

src/PIL/ImageFile.py

@@ -122,7 +122,7 @@ class ImageFile(Image.Image):
                 EOFError,  # got header but not the first frame
                 struct.error,
             ) as v:
-                raise SyntaxError(v)
+                raise SyntaxError(v) from v
 
             if not self.mode or self.size[0] <= 0:
                 raise SyntaxError("not identified by this driver")
@@ -241,12 +241,12 @@ class ImageFile(Image.Image):
                         while True:
                             try:
                                 s = read(self.decodermaxblock)
-                            except (IndexError, struct.error):
+                            except (IndexError, struct.error) as e:
                                 # truncated png/gif
                                 if LOAD_TRUNCATED_IMAGES:
                                     break
                                 else:
-                                    raise OSError("image file is truncated")
+                                    raise OSError("image file is truncated") from e
 
                             if not s:  # truncated jpeg
                                 if LOAD_TRUNCATED_IMAGES:
@@ -505,7 +505,7 @@ def _save(im, fp, tile, bufsize=0):
     try:
         fh = fp.fileno()
         fp.flush()
-    except (AttributeError, io.UnsupportedOperation):
+    except (AttributeError, io.UnsupportedOperation) as e:
         # compress to Python file-compatible object
         for e, b, o, a in tile:
             e = Image._getencoder(im.mode, e, a, im.encoderconfig)
@@ -522,7 +522,7 @@ def _save(im, fp, tile, bufsize=0):
                     if s:
                         break
             if s < 0:
-                raise OSError("encoder error %d when writing image file" % s)
+                raise OSError("encoder error %d when writing image file" % s) from e
             e.cleanup()
     else:
         # slight speedup: compress to real file object

src/PIL/ImageFilter.py

@@ -411,10 +411,10 @@ class Color3DLUT(MultibandFilter):
     def _check_size(size):
         try:
             _, _, _ = size
-        except ValueError:
+        except ValueError as e:
             raise ValueError(
                 "Size should be either an integer or a tuple of three integers."
-            )
+            ) from e
         except TypeError:
             size = (size, size, size)
         size = [int(x) for x in size]

src/PIL/ImageFont.py

@@ -503,8 +503,8 @@ class FreeTypeFont:
         """
         try:
             names = self.font.getvarnames()
-        except AttributeError:
+        except AttributeError as e:
-            raise NotImplementedError("FreeType 2.9.1 or greater is required")
+            raise NotImplementedError("FreeType 2.9.1 or greater is required") from e
         return [name.replace(b"\x00", b"") for name in names]
 
     def set_variation_by_name(self, name):
@@ -533,8 +533,8 @@ class FreeTypeFont:
         """
         try:
             axes = self.font.getvaraxes()
-        except AttributeError:
+        except AttributeError as e:
-            raise NotImplementedError("FreeType 2.9.1 or greater is required")
+            raise NotImplementedError("FreeType 2.9.1 or greater is required") from e
         for axis in axes:
             axis["name"] = axis["name"].replace(b"\x00", b"")
         return axes
@@ -546,8 +546,8 @@ class FreeTypeFont:
         """
         try:
             self.font.setvaraxes(axes)
-        except AttributeError:
+        except AttributeError as e:
-            raise NotImplementedError("FreeType 2.9.1 or greater is required")
+            raise NotImplementedError("FreeType 2.9.1 or greater is required") from e
 
 
 class TransposedFont:

src/PIL/ImageMath.py

@@ -57,8 +57,8 @@ class _Operand:
             im1.load()
             try:
                 op = getattr(_imagingmath, op + "_" + im1.mode)
-            except AttributeError:
+            except AttributeError as e:
-                raise TypeError("bad operand type for '%s'" % op)
+                raise TypeError("bad operand type for '%s'" % op) from e
             _imagingmath.unop(op, out.im.id, im1.im.id)
         else:
             # binary operation
@@ -85,8 +85,8 @@ class _Operand:
             im2.load()
             try:
                 op = getattr(_imagingmath, op + "_" + im1.mode)
-            except AttributeError:
+            except AttributeError as e:
-                raise TypeError("bad operand type for '%s'" % op)
+                raise TypeError("bad operand type for '%s'" % op) from e
             _imagingmath.binop(op, out.im.id, im1.im.id, im2.im.id)
         return _Operand(out)
 

src/PIL/ImagePalette.py

@@ -97,13 +97,13 @@ class ImagePalette:
         if isinstance(color, tuple):
             try:
                 return self.colors[color]
-            except KeyError:
+            except KeyError as e:
                 # allocate new color slot
                 if isinstance(self.palette, bytes):
                     self.palette = bytearray(self.palette)
                 index = len(self.colors)
                 if index >= 256:
-                    raise ValueError("cannot allocate more than 256 colors")
+                    raise ValueError("cannot allocate more than 256 colors") from e
                 self.colors[color] = index
                 self.palette[index] = color[0]
                 self.palette[index + 256] = color[1]

src/PIL/ImageSequence.py

@@ -38,8 +38,8 @@ class Iterator:
         try:
             self.im.seek(ix)
             return self.im
-        except EOFError:
+        except EOFError as e:
-            raise IndexError  # end of sequence
+            raise IndexError from e  # end of sequence
 
     def __iter__(self):
         return self
@@ -49,8 +49,8 @@ class Iterator:
             self.im.seek(self.position)
             self.position += 1
             return self.im
-        except EOFError:
+        except EOFError as e:
-            raise StopIteration
+            raise StopIteration from e
 
 
 def all_frames(im, func=None):

src/PIL/IptcImagePlugin.py

@@ -118,8 +118,8 @@ class IptcImageFile(ImageFile.ImageFile):
         # compression
         try:
             compression = COMPRESSION[self.getint((3, 120))]
-        except KeyError:
+        except KeyError as e:
-            raise OSError("Unknown IPTC image compression")
+            raise OSError("Unknown IPTC image compression") from e
 
         # tile
         if tag == (8, 10):

src/PIL/JpegImagePlugin.py

@@ -503,13 +503,13 @@ def _getmp(self):
         file_contents.seek(info.next)
         info.load(file_contents)
         mp = dict(info)
-    except Exception:
+    except Exception as e:
-        raise SyntaxError("malformed MP Index (unreadable directory)")
+        raise SyntaxError("malformed MP Index (unreadable directory)") from e
     # it's an error not to have a number of images
     try:
         quant = mp[0xB001]
-    except KeyError:
+    except KeyError as e:
-        raise SyntaxError("malformed MP Index (no number of images)")
+        raise SyntaxError("malformed MP Index (no number of images)") from e
     # get MP entries
     mpentries = []
     try:
@@ -545,8 +545,8 @@ def _getmp(self):
             mpentry["Attribute"] = mpentryattr
             mpentries.append(mpentry)
         mp[0xB002] = mpentries
-    except KeyError:
+    except KeyError as e:
-        raise SyntaxError("malformed MP Index (bad MP Entry)")
+        raise SyntaxError("malformed MP Index (bad MP Entry)") from e
     # Next we should try and parse the individual image unique ID list;
     # we don't because I've never seen this actually used in a real MPO
     # file and so can't test it.
@@ -610,8 +610,8 @@ def _save(im, fp, filename):
 
     try:
         rawmode = RAWMODE[im.mode]
-    except KeyError:
+    except KeyError as e:
-        raise OSError("cannot write mode %s as JPEG" % im.mode)
+        raise OSError("cannot write mode %s as JPEG" % im.mode) from e
 
     info = im.encoderinfo
 
@@ -663,8 +663,8 @@ def _save(im, fp, filename):
                     for line in qtables.splitlines()
                     for num in line.split("#", 1)[0].split()
                 ]
-            except ValueError:
+            except ValueError as e:
-                raise ValueError("Invalid quantization table")
+                raise ValueError("Invalid quantization table") from e
             else:
                 qtables = [lines[s : s + 64] for s in range(0, len(lines), 64)]
         if isinstance(qtables, (tuple, list, dict)):
@@ -679,8 +679,8 @@ def _save(im, fp, filename):
                     if len(table) != 64:
                         raise TypeError
                     table = array.array("B", table)
-                except TypeError:
+                except TypeError as e:
-                    raise ValueError("Invalid quantization table")
+                    raise ValueError("Invalid quantization table") from e
                 else:
                     qtables[idx] = list(table)
             return qtables

src/PIL/MicImagePlugin.py

@@ -46,8 +46,8 @@ class MicImageFile(TiffImagePlugin.TiffImageFile):
 
         try:
             self.ole = olefile.OleFileIO(self.fp)
-        except OSError:
+        except OSError as e:
-            raise SyntaxError("not an MIC file; invalid OLE file")
+            raise SyntaxError("not an MIC file; invalid OLE file") from e
 
         # find ACI subfiles with Image members (maybe not the
         # best way to identify MIC files, but what the... ;-)
@@ -77,8 +77,8 @@ class MicImageFile(TiffImagePlugin.TiffImageFile):
             return
         try:
             filename = self.images[frame]
-        except IndexError:
+        except IndexError as e:
-            raise EOFError("no such frame")
+            raise EOFError("no such frame") from e
 
         self.fp = self.ole.openstream(filename)
 

src/PIL/MspImagePlugin.py

@@ -116,8 +116,8 @@ class MspDecoder(ImageFile.PyDecoder):
             rowmap = struct.unpack_from(
                 "<%dH" % (self.state.ysize), self.fd.read(self.state.ysize * 2)
             )
-        except struct.error:
+        except struct.error as e:
-            raise OSError("Truncated MSP file in row map")
+            raise OSError("Truncated MSP file in row map") from e
 
         for x, rowlen in enumerate(rowmap):
             try:
@@ -142,8 +142,8 @@ class MspDecoder(ImageFile.PyDecoder):
                         img.write(row[idx : idx + runcount])
                         idx += runcount
 
-            except struct.error:
+            except struct.error as e:
-                raise OSError("Corrupted MSP file in row %d" % x)
+                raise OSError("Corrupted MSP file in row %d" % x) from e
 
         self.set_as_raw(img.getvalue(), ("1", 0, 1))
 

src/PIL/PcxImagePlugin.py

@@ -131,8 +131,8 @@ def _save(im, fp, filename):
 
     try:
         version, bits, planes, rawmode = SAVE[im.mode]
-    except KeyError:
+    except KeyError as e:
-        raise ValueError("Cannot save %s images as PCX" % im.mode)
+        raise ValueError("Cannot save %s images as PCX" % im.mode) from e
 
     # bytes per plane
     stride = (im.size[0] * bits + 7) // 8

src/PIL/PngImagePlugin.py

@@ -168,8 +168,10 @@ class ChunkStream:
             crc2 = i32(self.fp.read(4))
             if crc1 != crc2:
                 raise SyntaxError("broken PNG file (bad header checksum in %r)" % cid)
-        except struct.error:
+        except struct.error as e:
-            raise SyntaxError("broken PNG file (incomplete checksum in %r)" % cid)
+            raise SyntaxError(
+                "broken PNG file (incomplete checksum in %r)" % cid
+            ) from e
 
     def crc_skip(self, cid, data):
         """Read checksum.  Used if the C module is not present"""
@@ -186,8 +188,8 @@ class ChunkStream:
         while True:
             try:
                 cid, pos, length = self.read()
-            except struct.error:
+            except struct.error as e:
-                raise OSError("truncated PNG file")
+                raise OSError("truncated PNG file") from e
 
             if cid == endchunk:
                 break
@@ -737,9 +739,9 @@ class PngImageFile(ImageFile.ImageFile):
         for f in range(self.__frame + 1, frame + 1):
             try:
                 self._seek(f)
-            except EOFError:
+            except EOFError as e:
                 self.seek(last_frame)
-                raise EOFError("no more images in APNG file")
+                raise EOFError("no more images in APNG file") from e
 
     def _seek(self, frame, rewind=False):
         if frame == 0:
@@ -1168,8 +1170,8 @@ def _save(im, fp, filename, chunk=putchunk, save_all=False):
     # get the corresponding PNG mode
     try:
         rawmode, mode = _OUTMODES[mode]
-    except KeyError:
+    except KeyError as e:
-        raise OSError("cannot write mode %s as PNG" % mode)
+        raise OSError("cannot write mode %s as PNG" % mode) from e
 
     #
     # write minimal PNG file

src/PIL/PsdImagePlugin.py

@@ -144,8 +144,8 @@ class PsdImageFile(ImageFile.ImageFile):
             self.frame = layer
             self.fp = self.__fp
             return name, bbox
-        except IndexError:
+        except IndexError as e:
-            raise EOFError("no such layer")
+            raise EOFError("no such layer") from e
 
     def tell(self):
         # return layer number (0=image, 1..max=layers)

src/PIL/SpiderImagePlugin.py

@@ -111,8 +111,8 @@ class SpiderImageFile(ImageFile.ImageFile):
                 hdrlen = isSpiderHeader(t)
             if hdrlen == 0:
                 raise SyntaxError("not a valid Spider file")
-        except struct.error:
+        except struct.error as e:
-            raise SyntaxError("not a valid Spider file")
+            raise SyntaxError("not a valid Spider file") from e
 
         h = (99,) + t  # add 1 value : spider header index starts at 1
         iform = int(h[5])

src/PIL/TgaImagePlugin.py

@@ -167,8 +167,8 @@ def _save(im, fp, filename):
 
     try:
         rawmode, bits, colormaptype, imagetype = SAVE[im.mode]
-    except KeyError:
+    except KeyError as e:
-        raise OSError("cannot write mode %s as TGA" % im.mode)
+        raise OSError("cannot write mode %s as TGA" % im.mode) from e
 
     if "rle" in im.encoderinfo:
         rle = im.encoderinfo["rle"]

src/PIL/TiffImagePlugin.py

@@ -1117,8 +1117,8 @@ class TiffImageFile(ImageFile.ImageFile):
         )
         try:
             decoder.setimage(self.im, extents)
-        except ValueError:
+        except ValueError as e:
-            raise OSError("Couldn't set the image")
+            raise OSError("Couldn't set the image") from e
 
         close_self_fp = self._exclusive_fp and not self.is_animated
         if hasattr(self.fp, "getvalue"):
@@ -1231,9 +1231,9 @@ class TiffImageFile(ImageFile.ImageFile):
         logger.debug("format key: {}".format(key))
         try:
             self.mode, rawmode = OPEN_INFO[key]
-        except KeyError:
+        except KeyError as e:
             logger.debug("- unsupported format")
-            raise SyntaxError("unknown pixel mode")
+            raise SyntaxError("unknown pixel mode") from e
 
         logger.debug("- raw mode: {}".format(rawmode))
         logger.debug("- pil mode: {}".format(self.mode))
@@ -1400,8 +1400,8 @@ def _save(im, fp, filename):
 
     try:
         rawmode, prefix, photo, format, bits, extra = SAVE_INFO[im.mode]
-    except KeyError:
+    except KeyError as e:
-        raise OSError("cannot write mode %s as TIFF" % im.mode)
+        raise OSError("cannot write mode %s as TIFF" % im.mode) from e
 
     ifd = ImageFileDirectory_v2(prefix=prefix)