Issue #16304: Further performance improvements for BZ2File.

Optimizations suggested by Serhiy Storchaka.

Author: nvawda

Lib/bz2.py

@@ -159,15 +159,21 @@ def _check_not_closed(self):
             raise ValueError("I/O operation on closed file")
 
     def _check_can_read(self):
-        if not self.readable():
+        if self.closed:
+            raise ValueError("I/O operation on closed file")
+        if self._mode not in (_MODE_READ, _MODE_READ_EOF):
             raise io.UnsupportedOperation("File not open for reading")
 
     def _check_can_write(self):
-        if not self.writable():
+        if self.closed:
+            raise ValueError("I/O operation on closed file")
+        if self._mode != _MODE_WRITE:
             raise io.UnsupportedOperation("File not open for writing")
 
     def _check_can_seek(self):
-        if not self.readable():
+        if self.closed:
+            raise ValueError("I/O operation on closed file")
+        if self._mode not in (_MODE_READ, _MODE_READ_EOF):
             raise io.UnsupportedOperation("Seeking is only supported "
                                           "on files open for reading")
         if not self._fp.seekable():