convert-ly broken in 2.21.x?

[Stanton Sanderson]

I have had no response to my previous post, so I will try again.

On Mac OS 10.14.6 (Mojave), running LilyPond directly from the application and 
using Update Syntax” from the “Compile” menu, applying it to the “Welcome to 
Lilypond” file after renaming it “test 1.ly”, the following error message is 
produced:

---------
 Traceback (most recent call last):
  File "/Applications/LilyPond_2.21.4..app/Contents/Resources/bin/convert-ly", 
line 86, in <module>
    import convertrules
  File 
"/Applications/LilyPond_2.21.4..app/Contents/Resources/share/lilypond/current/python/convertrules.py",
 line 26, in <module>
    import lilylib
  File 
"/Applications/LilyPond_2.21.4..app/Contents/Resources/share/lilypond/current/python/lilylib.py",
 line 30, in <module>
    sys.stdin = codecs.getreader('utf8')(sys.stdin.detach())
AttributeError: 'file' object has no attribute ‘detach'
————

I saw the same behavior with 2.21.1 and 2.21.3 when I attempted to update older 
files.

What am I missing?

Thanks,

Stan