PyZ3950 - EncodingError: Bad type to bytes_write after porting to Python 3

Question

I am trying to connect to a database using PyZ3950 in a django application to retrieve data. This module is very old, and it has been working for Python 2, but I can't find a working version for Python 3.

https://github.com/danizen/PyZ3950 repo on github managed to port the application using 2to3.py and some hand changes, but although this library installs just fine, it throws the error PyZ3950.asn1.EncodingError: Bad type to bytes_write when I try the Connection method from zoom.

Here is the full Traceback:

Python 3.8.0 (tags/v3.8.0:fa919fd, Oct 14 2019, 19:21:23) [MSC v.1916 32 bit (Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.        
>>> from PyZ3950 import zoom
>>> conn = zoom.Connection ('z3950.loc.gov', 7090)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "D:\Downloads\Applications\PyZ3950-danizen\PyZ3950-master\PyZ3950\zoom.py", line 276, in __init__
    self.connect()
  File "D:\Downloads\Applications\PyZ3950-danizen\PyZ3950-master\PyZ3950\zoom.py", line 301, in connect
    self._cli = z3950.Client (self.host, self.port,
  File "D:\Downloads\Applications\PyZ3950-danizen\PyZ3950-master\PyZ3950\z3950.py", line 510, in __init__
    self.initresp = self.transact (
  File "D:\Downloads\Applications\PyZ3950-danizen\PyZ3950-master\PyZ3950\z3950.py", line 529, in transact
    b = self.encode_ctx.encode (APDU, to_send)
  File "D:\Downloads\Applications\PyZ3950-danizen\PyZ3950-master\PyZ3950\asn1.py", line 622, in encode
    spec.encode (self, data)
  File "D:\Downloads\Applications\PyZ3950-danizen\PyZ3950-master\PyZ3950\asn1.py", line 1192, in encode
    ctyp.encode (ctx, val)
  File "D:\Downloads\Applications\PyZ3950-danizen\PyZ3950-master\PyZ3950\asn1.py", line 858, in encode
    self.typ.encode (ctx, val)
  File "D:\Downloads\Applications\PyZ3950-danizen\PyZ3950-master\PyZ3950\asn1.py", line 796, in encode
    self.encode_val (ctx, val)
  File "D:\Downloads\Applications\PyZ3950-danizen\PyZ3950-master\PyZ3950\asn1.py", line 1504, in encode_val
    typ.encode (ctx, v)
  File "D:\Downloads\Applications\PyZ3950-danizen\PyZ3950-master\PyZ3950\asn1.py", line 858, in encode
    self.typ.encode (ctx, val)
  File "D:\Downloads\Applications\PyZ3950-danizen\PyZ3950-master\PyZ3950\asn1.py", line 796, in encode
    self.encode_val (ctx, val)
  File "D:\Downloads\Applications\PyZ3950-danizen\PyZ3950-master\PyZ3950\asn1.py", line 1089, in encode_val
    ctx.bytes_write (val)
  File "D:\Downloads\Applications\PyZ3950-danizen\PyZ3950-master\PyZ3950\asn1.py", line 633, in bytes_write
    raise EncodingError("Bad type to bytes_write")
PyZ3950.asn1.EncodingError: Bad type to bytes_write

Answer 1

Although I can't specifically answer your question, I have attempted to update the PyZ3959 code, starting with the work of Dan Davis: https://github.com/danizen/PyZ3950.

I did not try to make the code compatible with both Python 2 and 3, but concentrated on getting it to work with Python 3.7. The code may be found here: https://github.com/heaphey/PyZ3950

I have not tested it in a systematic way (as I believe Dan was doing), but have got it working well enough to fetch MARC records from OCLC, etc.