codecs.StreamRecoder not doing what I expected.

[D'Arcy J.M. Cain]

More Unicode bafflement.  What I am trying to do is pretty simple I
think.  I have a bunch of files that I am pretty sure are either utf-8
or iso-8859-1.  I try utf-8 and fall back to iso-8859-1 if it throws a
UnicodeError.  Here is my test.

#! /usr/pkg/bin/python3.4
# Running on a NetBSD 7.0 server
# Installed with pkgsrc

import codecs
test_file = "StreamRecoder.txt"

def read_file(fn):
    try: return open(fn, "r", encoding='utf-8').read()
    except UnicodeError:
        return codecs.StreamRecoder(open(fn),
            codecs.getencoder('utf-8'),
            codecs.getdecoder('utf-8'),
            codecs.getreader('iso-8859-1'),
            codecs.getwriter('iso-8859-1'), "r").read()

# plain ASCII
open(test_file, 'wb').write(b'abc - cents\n')
print(read_file(test_file))

# utf-8
open(test_file, 'wb').write(b'abc - \xc2\xa2\n')
print(read_file(test_file))

# iso-8859-1
open(test_file, 'wb').write(b'abc - \xa2\n')
print(read_file(test_file))

I expected all three to return UTF-8 strings but here is my output:

abc - cents

abc - ¢

Traceback (most recent call last):
  File "./StreamRecoder_test", line 9, in read_file
    try: return open(fn, "r", encoding='utf-8').read()
  File "/usr/pkg/lib/python3.4/codecs.py", line 319, in decode
    (result, consumed) = self._buffer_decode(data, self.errors, final)
UnicodeDecodeError: 'utf-8' codec can't decode byte 0xa2 in position 6:
invalid start byte

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "./StreamRecoder_test", line 27, in <module>
    print(read_file(test_file))
  File "./StreamRecoder_test", line 15, in read_file
    codecs.getwriter('iso-8859-1'), "r").read()
  File "/usr/pkg/lib/python3.4/codecs.py", line 798, in read
    data = self.reader.read(size)
  File "/usr/pkg/lib/python3.4/codecs.py", line 489, in read
    newdata = self.stream.read()
  File "/usr/pkg/lib/python3.4/encodings/ascii.py", line 26, in decode
    return codecs.ascii_decode(input, self.errors)[0]
UnicodeDecodeError: 'ascii' codec can't decode byte 0xa2 in position 6:
ordinal not in range(128)

-- 
D'Arcy J.M. Cain
Vybe Networks Inc.
http://www.VybeNetworks.com/
IM:darcy at Vex.Net VoIP: sip:darcy at VybeNetworks.com