Issue #9293: I/O streams now raise `io.UnsupportedOperation` when an
unsupported operation is attempted (for example, writing to a file open
only for reading).
diff --git a/Lib/_pyio.py b/Lib/_pyio.py
index 66f990d..12ae4b6 100644
--- a/Lib/_pyio.py
+++ b/Lib/_pyio.py
@@ -243,8 +243,13 @@
return open(*args, **kwargs)
-class UnsupportedOperation(ValueError, IOError):
- pass
+# In normal operation, both `UnsupportedOperation`s should be bound to the
+# same object.
+try:
+ UnsupportedOperation = io.UnsupportedOperation
+except AttributeError:
+ class UnsupportedOperation(ValueError, IOError):
+ pass
class IOBase(metaclass=abc.ABCMeta):
@@ -362,9 +367,8 @@
"""Internal: raise an IOError if file is not seekable
"""
if not self.seekable():
- raise IOError("File or stream is not seekable."
- if msg is None else msg)
-
+ raise UnsupportedOperation("File or stream is not seekable."
+ if msg is None else msg)
def readable(self) -> bool:
"""Return whether object was opened for reading.
@@ -377,8 +381,8 @@
"""Internal: raise an IOError if file is not readable
"""
if not self.readable():
- raise IOError("File or stream is not readable."
- if msg is None else msg)
+ raise UnsupportedOperation("File or stream is not readable."
+ if msg is None else msg)
def writable(self) -> bool:
"""Return whether object was opened for writing.
@@ -391,8 +395,8 @@
"""Internal: raise an IOError if file is not writable
"""
if not self.writable():
- raise IOError("File or stream is not writable."
- if msg is None else msg)
+ raise UnsupportedOperation("File or stream is not writable."
+ if msg is None else msg)
@property
def closed(self):
@@ -1647,7 +1651,7 @@
def tell(self):
if not self._seekable:
- raise IOError("underlying stream is not seekable")
+ raise UnsupportedOperation("underlying stream is not seekable")
if not self._telling:
raise IOError("telling position disabled by next() call")
self.flush()
@@ -1726,17 +1730,17 @@
if self.closed:
raise ValueError("tell on closed file")
if not self._seekable:
- raise IOError("underlying stream is not seekable")
+ raise UnsupportedOperation("underlying stream is not seekable")
if whence == 1: # seek relative to current position
if cookie != 0:
- raise IOError("can't do nonzero cur-relative seeks")
+ raise UnsupportedOperation("can't do nonzero cur-relative seeks")
# Seeking to the current position should attempt to
# sync the underlying buffer with the current position.
whence = 0
cookie = self.tell()
if whence == 2: # seek relative to end of file
if cookie != 0:
- raise IOError("can't do nonzero end-relative seeks")
+ raise UnsupportedOperation("can't do nonzero end-relative seeks")
self.flush()
position = self.buffer.seek(0, 2)
self._set_decoded_chars('')