Close #20404: blacklist non-text encodings in io.TextIOWrapper

- io.TextIOWrapper (and hence the open() builtin) now use the
  internal codec marking system added for issue #19619
- also tweaked the C code to only look up the encoding once,
  rather than multiple times
- the existing output type checks remain in place to deal with
  unmarked third party codecs.

1 files changed, 5 insertions, 0 deletions

diff --git a/Lib/_pyio.py b/Lib/_pyio.py
index 3961969..b04d23a 100644
--- a/Lib/_pyio.py
+++ b/Lib/_pyio.py
@@ -1503,6 +1503,11 @@ class TextIOWrapper(TextIOBase):
         if not isinstance(encoding, str):
             raise ValueError("invalid encoding: %r" % encoding)
 
+        if not codecs.lookup(encoding)._is_text_encoding:
+            msg = ("%r is not a text encoding; "
+                   "use codecs.open() to handle arbitrary codecs")
+            raise LookupError(msg % encoding)
+
         if errors is None:
             errors = "strict"
         else: