Merge pull request #8761 from hugovk/slice-startswith

Replace slice and comparison with `startswith`/`endswith`

Tests/test_file_mpo.py

@@ -77,8 +77,8 @@ def test_app(test_file: str) -> None:
     with Image.open(test_file) as im:
         assert im.applist[0][0] == "APP1"
         assert im.applist[1][0] == "APP2"
-        assert (
-            im.applist[1][1][:16] == b"MPF\x00MM\x00*\x00\x00\x00\x08\x00\x03\xb0\x00"
+        assert im.applist[1][1].startswith(
+            b"MPF\x00MM\x00*\x00\x00\x00\x08\x00\x03\xb0\x00"
         )
         assert len(im.applist) == 2
 

Tests/test_file_webp_metadata.py

@@ -40,7 +40,7 @@ def test_read_exif_metadata() -> None:
 def test_read_exif_metadata_without_prefix() -> None:
     with Image.open("Tests/images/flower2.webp") as im:
         # Assert prefix is not present
-        assert im.info["exif"][:6] != b"Exif\x00\x00"
+        assert not im.info["exif"].startswith(b"Exif\x00\x00")
 
         exif = im.getexif()
         assert exif[305] == "Adobe Photoshop CS6 (Macintosh)"

Tests/test_image.py

@@ -74,12 +74,12 @@ class TestImage:
 
     def test_sanity(self) -> None:
         im = Image.new("L", (100, 100))
-        assert repr(im)[:45] == "<PIL.Image.Image image mode=L size=100x100 at"
+        assert repr(im).startswith("<PIL.Image.Image image mode=L size=100x100 at")
         assert im.mode == "L"
         assert im.size == (100, 100)
 
         im = Image.new("RGB", (100, 100))
-        assert repr(im)[:45] == "<PIL.Image.Image image mode=RGB size=100x100 "
+        assert repr(im).startswith("<PIL.Image.Image image mode=RGB size=100x100 ")
         assert im.mode == "RGB"
         assert im.size == (100, 100)
 

docs/example/DdsImagePlugin.py

@@ -285,7 +285,7 @@ Image.register_decoder("DXT5", DXT5Decoder)
 
 
 def _accept(prefix: bytes) -> bool:
-    return prefix[:4] == b"DDS "
+    return prefix.startswith(b"DDS ")
 
 
 Image.register_open(DdsImageFile.format, DdsImageFile, _accept)

docs/handbook/writing-your-own-image-plugin.rst

@@ -54,7 +54,7 @@ true color.
 
 
     def _accept(prefix: bytes) -> bool:
-        return prefix[:4] == b"SPAM"
+        return prefix.startswith(b"SPAM")
 
 
     class SpamImageFile(ImageFile.ImageFile):

src/PIL/BdfFontFile.py

@@ -43,7 +43,7 @@ def bdf_char(
         s = f.readline()
         if not s:
             return None
-        if s[:9] == b"STARTCHAR":
+        if s.startswith(b"STARTCHAR"):
             break
     id = s[9:].strip().decode("ascii")
 
@@ -51,7 +51,7 @@ def bdf_char(
     props = {}
     while True:
         s = f.readline()
-        if not s or s[:6] == b"BITMAP":
+        if not s or s.startswith(b"BITMAP"):
             break
         i = s.find(b" ")
         props[s[:i].decode("ascii")] = s[i + 1 : -1].decode("ascii")
@@ -60,7 +60,7 @@ def bdf_char(
     bitmap = bytearray()
     while True:
         s = f.readline()
-        if not s or s[:7] == b"ENDCHAR":
+        if not s or s.startswith(b"ENDCHAR"):
             break
         bitmap += s[:-1]
 
@@ -96,7 +96,7 @@ class BdfFontFile(FontFile.FontFile):
         super().__init__()
 
         s = fp.readline()
-        if s[:13] != b"STARTFONT 2.1":
+        if not s.startswith(b"STARTFONT 2.1"):
             msg = "not a valid BDF file"
             raise SyntaxError(msg)
 
@@ -105,7 +105,7 @@ class BdfFontFile(FontFile.FontFile):
 
         while True:
             s = fp.readline()
-            if not s or s[:13] == b"ENDPROPERTIES":
+            if not s or s.startswith(b"ENDPROPERTIES"):
                 break
             i = s.find(b" ")
             props[s[:i].decode("ascii")] = s[i + 1 : -1].decode("ascii")

src/PIL/BlpImagePlugin.py

@@ -246,7 +246,7 @@ class BLPFormatError(NotImplementedError):
 
 
 def _accept(prefix: bytes) -> bool:
-    return prefix[:4] in (b"BLP1", b"BLP2")
+    return prefix.startswith((b"BLP1", b"BLP2"))
 
 
 class BlpImageFile(ImageFile.ImageFile):

src/PIL/BmpImagePlugin.py

@@ -50,7 +50,7 @@ BIT2MODE = {
 
 
 def _accept(prefix: bytes) -> bool:
-    return prefix[:2] == b"BM"
+    return prefix.startswith(b"BM")
 
 
 def _dib_accept(prefix: bytes) -> bool:

src/PIL/BufrStubImagePlugin.py

@@ -33,7 +33,7 @@ def register_handler(handler: ImageFile.StubHandler | None) -> None:
 
 
 def _accept(prefix: bytes) -> bool:
-    return prefix[:4] == b"BUFR" or prefix[:4] == b"ZCZC"
+    return prefix.startswith((b"BUFR", b"ZCZC"))
 
 
 class BufrStubImageFile(ImageFile.StubImageFile):

src/PIL/CurImagePlugin.py

@@ -26,7 +26,7 @@ from ._binary import i32le as i32
 
 
 def _accept(prefix: bytes) -> bool:
-    return prefix[:4] == b"\0\0\2\0"
+    return prefix.startswith(b"\0\0\2\0")
 
 
 ##

src/PIL/DdsImagePlugin.py

@@ -564,7 +564,7 @@ def _save(im: Image.Image, fp: IO[bytes], filename: str | bytes) -> None:
 
 
 def _accept(prefix: bytes) -> bool:
-    return prefix[:4] == b"DDS "
+    return prefix.startswith(b"DDS ")
 
 
 Image.register_open(DdsImageFile.format, DdsImageFile, _accept)

src/PIL/EpsImagePlugin.py

@@ -170,7 +170,9 @@ def Ghostscript(
 
 
 def _accept(prefix: bytes) -> bool:
-    return prefix[:4] == b"%!PS" or (len(prefix) >= 4 and i32(prefix) == 0xC6D3D0C5)
+    return prefix.startswith(b"%!PS") or (
+        len(prefix) >= 4 and i32(prefix) == 0xC6D3D0C5
+    )
 
 
 ##
@@ -295,7 +297,7 @@ class EpsImageFile(ImageFile.ImageFile):
                     m = field.match(s)
                     if m:
                         k = m.group(1)
-                        if k[:8] == "PS-Adobe":
+                        if k.startswith("PS-Adobe"):
                             self.info["PS-Adobe"] = k[9:]
                         else:
                             self.info[k] = ""

src/PIL/FitsImagePlugin.py

@@ -17,7 +17,7 @@ from . import Image, ImageFile
 
 
 def _accept(prefix: bytes) -> bool:
-    return prefix[:6] == b"SIMPLE"
+    return prefix.startswith(b"SIMPLE")
 
 
 class FitsImageFile(ImageFile.ImageFile):

src/PIL/FpxImagePlugin.py

@@ -42,7 +42,7 @@ MODES = {
 
 
 def _accept(prefix: bytes) -> bool:
-    return prefix[:8] == olefile.MAGIC
+    return prefix.startswith(olefile.MAGIC)
 
 
 ##

src/PIL/FtexImagePlugin.py

@@ -108,7 +108,7 @@ class FtexImageFile(ImageFile.ImageFile):
 
 
 def _accept(prefix: bytes) -> bool:
-    return prefix[:4] == MAGIC
+    return prefix.startswith(MAGIC)
 
 
 Image.register_open(FtexImageFile.format, FtexImageFile, _accept)

src/PIL/GifImagePlugin.py

@@ -67,7 +67,7 @@ LOADING_STRATEGY = LoadingStrategy.RGB_AFTER_FIRST
 
 
 def _accept(prefix: bytes) -> bool:
-    return prefix[:6] in [b"GIF87a", b"GIF89a"]
+    return prefix.startswith((b"GIF87a", b"GIF89a"))
 
 
 ##
@@ -257,7 +257,7 @@ class GifImageFile(ImageFile.ImageFile):
                     # application extension
                     #
                     info["extension"] = block, self.fp.tell()
-                    if block[:11] == b"NETSCAPE2.0":
+                    if block.startswith(b"NETSCAPE2.0"):
                         block = self.data()
                         if block and len(block) >= 3 and block[0] == 1:
                             self.info["loop"] = i16(block, 1)

src/PIL/GimpGradientFile.py

@@ -116,7 +116,7 @@ class GimpGradientFile(GradientFile):
     """File handler for GIMP's gradient format."""
 
     def __init__(self, fp: IO[bytes]) -> None:
-        if fp.readline()[:13] != b"GIMP Gradient":
+        if not fp.readline().startswith(b"GIMP Gradient"):
             msg = "not a GIMP gradient file"
             raise SyntaxError(msg)
 

src/PIL/GimpPaletteFile.py

@@ -29,7 +29,7 @@ class GimpPaletteFile:
     def __init__(self, fp: IO[bytes]) -> None:
         palette = [o8(i) * 3 for i in range(256)]
 
-        if fp.readline()[:12] != b"GIMP Palette":
+        if not fp.readline().startswith(b"GIMP Palette"):
             msg = "not a GIMP palette file"
             raise SyntaxError(msg)
 

src/PIL/GribStubImagePlugin.py

@@ -33,7 +33,7 @@ def register_handler(handler: ImageFile.StubHandler | None) -> None:
 
 
 def _accept(prefix: bytes) -> bool:
-    return prefix[:4] == b"GRIB" and prefix[7] == 1
+    return prefix.startswith(b"GRIB") and prefix[7] == 1
 
 
 class GribStubImageFile(ImageFile.StubImageFile):

src/PIL/Hdf5StubImagePlugin.py

@@ -33,7 +33,7 @@ def register_handler(handler: ImageFile.StubHandler | None) -> None:
 
 
 def _accept(prefix: bytes) -> bool:
-    return prefix[:8] == b"\x89HDF\r\n\x1a\n"
+    return prefix.startswith(b"\x89HDF\r\n\x1a\n")
 
 
 class HDF5StubImageFile(ImageFile.StubImageFile):

src/PIL/IcnsImagePlugin.py

@@ -117,14 +117,14 @@ def read_png_or_jpeg2000(
     sig = fobj.read(12)
 
     im: Image.Image
-    if sig[:8] == b"\x89PNG\x0d\x0a\x1a\x0a":
+    if sig.startswith(b"\x89PNG\x0d\x0a\x1a\x0a"):
         fobj.seek(start)
         im = PngImagePlugin.PngImageFile(fobj)
         Image._decompression_bomb_check(im.size)
         return {"RGBA": im}
     elif (
-        sig[:4] == b"\xff\x4f\xff\x51"
-        or sig[:4] == b"\x0d\x0a\x87\x0a"
+        sig.startswith(b"\xff\x4f\xff\x51")
+        or sig.startswith(b"\x0d\x0a\x87\x0a")
         or sig == b"\x00\x00\x00\x0cjP  \x0d\x0a\x87\x0a"
     ):
         if not enable_jpeg2k:
@@ -387,7 +387,7 @@ def _save(im: Image.Image, fp: IO[bytes], filename: str | bytes) -> None:
 
 
 def _accept(prefix: bytes) -> bool:
-    return prefix[:4] == MAGIC
+    return prefix.startswith(MAGIC)
 
 
 Image.register_open(IcnsImageFile.format, IcnsImageFile, _accept)

src/PIL/IcoImagePlugin.py

@@ -118,7 +118,7 @@ def _save(im: Image.Image, fp: IO[bytes], filename: str | bytes) -> None:
 
 
 def _accept(prefix: bytes) -> bool:
-    return prefix[:4] == _MAGIC
+    return prefix.startswith(_MAGIC)
 
 
 class IconHeader(NamedTuple):

src/PIL/ImImagePlugin.py

@@ -155,9 +155,9 @@ class ImImageFile(ImageFile.ImageFile):
                 msg = "not an IM file"
                 raise SyntaxError(msg)
 
-            if s[-2:] == b"\r\n":
+            if s.endswith(b"\r\n"):
                 s = s[:-2]
-            elif s[-1:] == b"\n":
+            elif s.endswith(b"\n"):
                 s = s[:-1]
 
             try:
@@ -209,7 +209,7 @@ class ImImageFile(ImageFile.ImageFile):
         self._mode = self.info[MODE]
 
         # Skip forward to start of image data
-        while s and s[:1] != b"\x1a":
+        while s and not s.startswith(b"\x1a"):
             s = self.fp.read(1)
         if not s:
             msg = "File truncated"
@@ -247,7 +247,7 @@ class ImImageFile(ImageFile.ImageFile):
 
         self._fp = self.fp  # FIXME: hack
 
-        if self.rawmode[:2] == "F;":
+        if self.rawmode.startswith("F;"):
             # ifunc95 formats
             try:
                 # use bit decoder (if necessary)

src/PIL/Image.py

@@ -3998,7 +3998,7 @@ class Exif(_ExifBase):
                 if tag == ExifTags.IFD.MakerNote:
                     from .TiffImagePlugin import ImageFileDirectory_v2
 
-                    if tag_data[:8] == b"FUJIFILM":
+                    if tag_data.startswith(b"FUJIFILM"):
                         ifd_offset = i32le(tag_data, 8)
                         ifd_data = tag_data[ifd_offset:]
 

src/PIL/Jpeg2KImagePlugin.py

@@ -352,9 +352,8 @@ class Jpeg2KImageFile(ImageFile.ImageFile):
 
 
 def _accept(prefix: bytes) -> bool:
-    return (
-        prefix[:4] == b"\xff\x4f\xff\x51"
-        or prefix[:12] == b"\x00\x00\x00\x0cjP  \x0d\x0a\x87\x0a"
+    return prefix.startswith(
+        (b"\xff\x4f\xff\x51", b"\x00\x00\x00\x0cjP  \x0d\x0a\x87\x0a")
     )
 
 

src/PIL/JpegImagePlugin.py

@@ -77,7 +77,7 @@ def APP(self: JpegImageFile, marker: int) -> None:
     self.app[app] = s  # compatibility
     self.applist.append((app, s))
 
-    if marker == 0xFFE0 and s[:4] == b"JFIF":
+    if marker == 0xFFE0 and s.startswith(b"JFIF"):
         # extract JFIF information
         self.info["jfif"] = version = i16(s, 5)  # version
         self.info["jfif_version"] = divmod(version, 256)
@@ -95,19 +95,19 @@ def APP(self: JpegImageFile, marker: int) -> None:
                 self.info["dpi"] = tuple(d * 2.54 for d in jfif_density)
             self.info["jfif_unit"] = jfif_unit
             self.info["jfif_density"] = jfif_density
-    elif marker == 0xFFE1 and s[:6] == b"Exif\0\0":
+    elif marker == 0xFFE1 and s.startswith(b"Exif\0\0"):
         # extract EXIF information
         if "exif" in self.info:
             self.info["exif"] += s[6:]
         else:
             self.info["exif"] = s
             self._exif_offset = self.fp.tell() - n + 6
-    elif marker == 0xFFE1 and s[:29] == b"http://ns.adobe.com/xap/1.0/\x00":
+    elif marker == 0xFFE1 and s.startswith(b"http://ns.adobe.com/xap/1.0/\x00"):
         self.info["xmp"] = s.split(b"\x00", 1)[1]
-    elif marker == 0xFFE2 and s[:5] == b"FPXR\0":
+    elif marker == 0xFFE2 and s.startswith(b"FPXR\0"):
         # extract FlashPix information (incomplete)
         self.info["flashpix"] = s  # FIXME: value will change
-    elif marker == 0xFFE2 and s[:12] == b"ICC_PROFILE\0":
+    elif marker == 0xFFE2 and s.startswith(b"ICC_PROFILE\0"):
         # Since an ICC profile can be larger than the maximum size of
         # a JPEG marker (64K), we need provisions to split it into
         # multiple markers. The format defined by the ICC specifies
@@ -120,7 +120,7 @@ def APP(self: JpegImageFile, marker: int) -> None:
         # reassemble the profile, rather than assuming that the APP2
         # markers appear in the correct sequence.
         self.icclist.append(s)
-    elif marker == 0xFFED and s[:14] == b"Photoshop 3.0\x00":
+    elif marker == 0xFFED and s.startswith(b"Photoshop 3.0\x00"):
         # parse the image resource block
         offset = 14
         photoshop = self.info.setdefault("photoshop", {})
@@ -153,7 +153,7 @@ def APP(self: JpegImageFile, marker: int) -> None:
             except struct.error:
                 break  # insufficient data
 
-    elif marker == 0xFFEE and s[:5] == b"Adobe":
+    elif marker == 0xFFEE and s.startswith(b"Adobe"):
         self.info["adobe"] = i16(s, 5)
         # extract Adobe custom properties
         try:
@@ -162,7 +162,7 @@ def APP(self: JpegImageFile, marker: int) -> None:
             pass
         else:
             self.info["adobe_transform"] = adobe_transform
-    elif marker == 0xFFE2 and s[:4] == b"MPF\0":
+    elif marker == 0xFFE2 and s.startswith(b"MPF\0"):
         # extract MPO information
         self.info["mp"] = s[4:]
         # offset is current location minus buffer size
@@ -325,7 +325,7 @@ MARKER = {
 
 def _accept(prefix: bytes) -> bool:
     # Magic number was taken from https://en.wikipedia.org/wiki/JPEG
-    return prefix[:3] == b"\xff\xd8\xff"
+    return prefix.startswith(b"\xff\xd8\xff")
 
 
 ##
@@ -547,7 +547,7 @@ def _getmp(self: JpegImageFile) -> dict[int, Any] | None:
         return None
     file_contents = io.BytesIO(data)
     head = file_contents.read(8)
-    endianness = ">" if head[:4] == b"\x4d\x4d\x00\x2a" else "<"
+    endianness = ">" if head.startswith(b"\x4d\x4d\x00\x2a") else "<"
     # process dictionary
     from . import TiffImagePlugin
 

src/PIL/McIdasImagePlugin.py

@@ -23,7 +23,7 @@ from . import Image, ImageFile
 
 
 def _accept(prefix: bytes) -> bool:
-    return prefix[:8] == b"\x00\x00\x00\x00\x00\x00\x00\x04"
+    return prefix.startswith(b"\x00\x00\x00\x00\x00\x00\x00\x04")
 
 
 ##

src/PIL/MicImagePlugin.py

@@ -26,7 +26,7 @@ from . import Image, TiffImagePlugin
 
 
 def _accept(prefix: bytes) -> bool:
-    return prefix[:8] == olefile.MAGIC
+    return prefix.startswith(olefile.MAGIC)
 
 
 ##
@@ -54,7 +54,7 @@ class MicImageFile(TiffImagePlugin.TiffImageFile):
         self.images = [
             path
             for path in self.ole.listdir()
-            if path[1:] and path[0][-4:] == ".ACI" and path[1] == "Image"
+            if path[1:] and path[0].endswith(".ACI") and path[1] == "Image"
         ]
 
         # if we didn't find any images, this is probably not

src/PIL/MpegImagePlugin.py

@@ -54,7 +54,7 @@ class BitStream:
 
 
 def _accept(prefix: bytes) -> bool:
-    return prefix[:4] == b"\x00\x00\x01\xb3"
+    return prefix.startswith(b"\x00\x00\x01\xb3")
 
 
 ##

src/PIL/MspImagePlugin.py

@@ -37,7 +37,7 @@ from ._binary import o16le as o16
 
 
 def _accept(prefix: bytes) -> bool:
-    return prefix[:4] in [b"DanM", b"LinS"]
+    return prefix.startswith((b"DanM", b"LinS"))
 
 
 ##
@@ -69,7 +69,7 @@ class MspImageFile(ImageFile.ImageFile):
         self._mode = "1"
         self._size = i16(s, 4), i16(s, 6)
 
-        if s[:4] == b"DanM":
+        if s.startswith(b"DanM"):
             self.tile = [ImageFile._Tile("raw", (0, 0) + self.size, 32, "1")]
         else:
             self.tile = [ImageFile._Tile("MSP", (0, 0) + self.size, 32)]

src/PIL/PaletteFile.py

@@ -32,7 +32,7 @@ class PaletteFile:
 
             if not s:
                 break
-            if s[:1] == b"#":
+            if s.startswith(b"#"):
                 continue
             if len(s) > 100:
                 msg = "bad palette file"

src/PIL/PcdImagePlugin.py

@@ -34,7 +34,7 @@ class PcdImageFile(ImageFile.ImageFile):
         self.fp.seek(2048)
         s = self.fp.read(2048)
 
-        if s[:4] != b"PCD_":
+        if not s.startswith(b"PCD_"):
             msg = "not a PCD file"
             raise SyntaxError(msg)
 

src/PIL/PixarImagePlugin.py

@@ -28,7 +28,7 @@ from ._binary import i16le as i16
 
 
 def _accept(prefix: bytes) -> bool:
-    return prefix[:4] == b"\200\350\000\000"
+    return prefix.startswith(b"\200\350\000\000")
 
 
 ##

src/PIL/PngImagePlugin.py

@@ -740,7 +740,7 @@ class PngStream(ChunkStream):
 
 
 def _accept(prefix: bytes) -> bool:
-    return prefix[:8] == _MAGIC
+    return prefix.startswith(_MAGIC)
 
 
 ##

src/PIL/PpmImagePlugin.py

@@ -47,7 +47,7 @@ MODES = {
 
 
 def _accept(prefix: bytes) -> bool:
-    return prefix[0:1] == b"P" and prefix[1] in b"0123456fy"
+    return prefix.startswith(b"P") and prefix[1] in b"0123456fy"
 
 
 ##

src/PIL/PsdImagePlugin.py

@@ -47,7 +47,7 @@ MODES = {
 
 
 def _accept(prefix: bytes) -> bool:
-    return prefix[:4] == b"8BPS"
+    return prefix.startswith(b"8BPS")
 
 
 ##

src/PIL/QoiImagePlugin.py

@@ -14,7 +14,7 @@ from ._binary import i32be as i32
 
 
 def _accept(prefix: bytes) -> bool:
-    return prefix[:4] == b"qoif"
+    return prefix.startswith(b"qoif")
 
 
 class QoiImageFile(ImageFile.ImageFile):

src/PIL/TiffImagePlugin.py

@@ -288,7 +288,7 @@ if not getattr(Image.core, "libtiff_support_custom_tags", True):
 
 
 def _accept(prefix: bytes) -> bool:
-    return prefix[:4] in PREFIXES
+    return prefix.startswith(tuple(PREFIXES))
 
 
 def _limit_rational(
@@ -1280,7 +1280,7 @@ class TiffImageFile(ImageFile.ImageFile):
         blocks = {}
         val = self.tag_v2.get(ExifTags.Base.ImageResources)
         if val:
-            while val[:4] == b"8BIM":
+            while val.startswith(b"8BIM"):
                 id = i16(val[4:6])
                 n = math.ceil((val[6] + 1) / 2) * 2
                 size = i32(val[6 + n : 10 + n])

src/PIL/WebPImagePlugin.py

@@ -21,7 +21,7 @@ _VP8_MODES_BY_IDENTIFIER = {
 
 
 def _accept(prefix: bytes) -> bool | str:
-    is_riff_file_format = prefix[:4] == b"RIFF"
+    is_riff_file_format = prefix.startswith(b"RIFF")
     is_webp_file = prefix[8:12] == b"WEBP"
     is_valid_vp8_mode = prefix[12:16] in _VP8_MODES_BY_IDENTIFIER
 

src/PIL/WmfImagePlugin.py

@@ -68,9 +68,7 @@ if hasattr(Image.core, "drawwmf"):
 
 
 def _accept(prefix: bytes) -> bool:
-    return (
-        prefix[:6] == b"\xd7\xcd\xc6\x9a\x00\x00" or prefix[:4] == b"\x01\x00\x00\x00"
-    )
+    return prefix.startswith((b"\xd7\xcd\xc6\x9a\x00\x00", b"\x01\x00\x00\x00"))
 
 
 ##
@@ -87,7 +85,7 @@ class WmfStubImageFile(ImageFile.StubImageFile):
         # check placable header
         s = self.fp.read(80)
 
-        if s[:6] == b"\xd7\xcd\xc6\x9a\x00\x00":
+        if s.startswith(b"\xd7\xcd\xc6\x9a\x00\x00"):
             # placeable windows metafile
 
             # get units per inch
@@ -116,7 +114,7 @@ class WmfStubImageFile(ImageFile.StubImageFile):
                 msg = "Unsupported WMF file format"
                 raise SyntaxError(msg)
 
-        elif s[:4] == b"\x01\x00\x00\x00" and s[40:44] == b" EMF":
+        elif s.startswith(b"\x01\x00\x00\x00") and s[40:44] == b" EMF":
             # enhanced metafile
 
             # get bounding box

src/PIL/XVThumbImagePlugin.py

@@ -34,7 +34,7 @@ for r in range(8):
 
 
 def _accept(prefix: bytes) -> bool:
-    return prefix[:6] == _MAGIC
+    return prefix.startswith(_MAGIC)
 
 
 ##

src/PIL/XbmImagePlugin.py

@@ -38,7 +38,7 @@ xbm_head = re.compile(
 
 
 def _accept(prefix: bytes) -> bool:
-    return prefix.lstrip()[:7] == b"#define"
+    return prefix.lstrip().startswith(b"#define")
 
 
 ##

src/PIL/XpmImagePlugin.py

@@ -25,7 +25,7 @@ xpm_head = re.compile(b'"([0-9]*) ([0-9]*) ([0-9]*) ([0-9]*)')
 
 
 def _accept(prefix: bytes) -> bool:
-    return prefix[:9] == b"/* XPM */"
+    return prefix.startswith(b"/* XPM */")
 
 
 ##
@@ -67,9 +67,9 @@ class XpmImageFile(ImageFile.ImageFile):
 
         for _ in range(pal):
             s = self.fp.readline()
-            if s[-2:] == b"\r\n":
+            if s.endswith(b"\r\n"):
                 s = s[:-2]
-            elif s[-1:] in b"\r\n":
+            elif s.endswith((b"\r", b"\n")):
                 s = s[:-1]
 
             c = s[1]
@@ -81,7 +81,7 @@ class XpmImageFile(ImageFile.ImageFile):
                     rgb = s[i + 1]
                     if rgb == b"None":
                         self.info["transparency"] = c
-                    elif rgb[:1] == b"#":
+                    elif rgb.startswith(b"#"):
                         # FIXME: handle colour names (see ImagePalette.py)
                         rgb = int(rgb[1:], 16)
                         palette[c] = (