For effiency, set newline character outside of loop

src/PIL/ContainerIO.py

@@ -93,12 +93,13 @@ def readline(self):
         :returns: An 8-bit string.
         """
         s = b"" if "b" in self.fh.mode else ""
+        newLineCharacter = b"\n" if "b" in self.fh.mode else "\n"
         while True:
             c = self.read(1)
             if not c:
                 break
             s = s + c
-            if c == (b"\n" if "b" in self.fh.mode else "\n"):
+            if c == newLineCharacter:
                 break
         return s