bpo-37388: Development mode check encoding and errors (GH-14341)

In development mode and in debug build, encoding and errors arguments
are now checked on string encoding and decoding operations. Examples:
open(), str.encode() and bytes.decode().

By default, for best performances, the errors argument is only
checked at the first encoding/decoding error, and the encoding
argument is sometimes ignored for empty strings.

1 files changed, 4 insertions, 0 deletions

diff --git a/Lib/_pyio.py b/Lib/_pyio.py
index 0b6493bc8d..c355164305 100644
--- a/Lib/_pyio.py
+++ b/Lib/_pyio.py
@@ -36,6 +36,8 @@ BlockingIOError = BlockingIOError
 # Does io.IOBase finalizer log the exception if the close() method fails?
 # The exception is ignored silently by default in release build.
 _IOBASE_EMITS_UNRAISABLE = (hasattr(sys, "gettotalrefcount") or sys.flags.dev_mode)
+# Does open() check its 'errors' argument?
+_CHECK_ERRORS = _IOBASE_EMITS_UNRAISABLE
 
 
 def open(file, mode="r", buffering=-1, encoding=None, errors=None,
@@ -2022,6 +2024,8 @@ class TextIOWrapper(TextIOBase):
         else:
             if not isinstance(errors, str):
                 raise ValueError("invalid errors: %r" % errors)
+            if _CHECK_ERRORS:
+                codecs.lookup_error(errors)
 
         self._buffer = buffer
         self._decoded_chars = ''  # buffer for text returned from decoder