[issue32268] quopri.decode(): string argument expected, got 'bytes'

[Christoph Reiter]

Change by Christoph Reiter :


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nosy:  -lazka

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[issue32268] quopri.decode(): string argument expected, got 'bytes'

[R. David Murray]

R. David Murray  added the comment:

Yes, if that protocol existed the errors would be clearer.  But it doesn't, for 
historical reasons, and that is unlikely to change.

You are welcome to submit an enhancement request to make quopri accept string 
as an argument when decoding.  But when encoding, it must produce bytes, 
because "ASCII" is a *byte* encoding, not a unicode encoding (unicode is ascii 
compatible, but it is neither ascii nor bytes).  You might have to write the PR 
yourself, I'm not sure if anyone else will be interested (but some of the 
people on the core-mentorship mailing list might be).

StringIO is specifically designed to only operate on strings.  If you want to 
decode the bytes you feed it, you have to do that.  This is an intentional 
design.

Further discussion of ways to improve the situation should move to the 
python-idea mailing list.  There's really nothing to do here from a bug tracker 
perspective, unless you want to open an enhancement request as mentioned above.

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[issue32268] quopri.decode(): string argument expected, got 'bytes'

[Alexey Luchko]

Alexey Luchko  added the comment:

1. On quopri.

It is counter-intuitive despite the clear statement in the doc-string. 
Quoted-printable is used mostly for text encoding. (It would be quite awkward 
and inefficient to use it for binary data.)

My case: I have a text and I mean to get a text. Why on earth StringIO is not 
suitable for this goal... It is just crazy!


2. On duck typing and StringIO.

It should make life easy, not crazy. But with great power... You know.

Taking a wider look than just quopri, the case shows a problem – writing text 
to StringIO produces a type error stating *string argument expected*.
That is crazy and as counter-duck-typing as type checking.
And even more ... crazy in case of 7bit ascii!

There could be a solution on StringIO side, like an encoding it should expect 
on input if it gets binary data. At least 7bit ascii would be totally ok for 
default it this case.
Then it either would have worked or would have produced a clear text encoding 
related error that would be *meaningful* and *instructive*.


3. On protocol.

A protocol: write_bytes() and write_string() methods that would have been 
raising type error in case of text_file.write_bytes() or 
binary_file.write_string().
Then one having bytes-*like* object (like quopri.decode) would call 
write_bytes() and StringIO would raise smth like 'StringIO used for binary 
output, consider BytesIO' or 'Text file requires strings, not bytes' that would 
be meaningful as well.
Other one having string-*like* object would call knowingly write_string() with 
a corresponding error from BytesIO or binary file.

*There is nothing of checking in the protocol, but clear intention statement.*

Disclaimer:
  It is just an example and an opinion. There is no reason for holy war.
  I don't pretend it would be any better...

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[issue32268] quopri.decode(): string argument expected, got 'bytes'

[R. David Murray]

R. David Murray  added the comment:

That's type checking.  Not type checking is to call the method that writes the 
data, expecting the object to handle the bytes it is passed, and then that 
object raises an error to indicate that it cannot.  There is no protocol that 
can be checked for.

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[issue32268] quopri.decode(): string argument expected, got 'bytes'

[Alexey Luchko]

Alexey Luchko  added the comment:

I didn't mean type checking. The point is that since string and bytes are 
different types, then binary and text files are actually much more different 
than before python 3. Therefore they better be of different protocols.
Then inside quopri with StringIO in place of BytesIO the error would be much 
more clear and this issue would not have appeared.
This would be helpful in lack of one's intuition, like with newcomers.

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[issue32268] quopri.decode(): string argument expected, got 'bytes'

[R. David Murray]

R. David Murray  added the comment:

We generally don't do advance type checking (look before you leap) in Python.  
This allows a type the programmer hadn't planned for to be used as long as it 
"quacks like" the expected type (this is called duck typing).  So the error was 
produced exactly where it should be and exactly as it should be: it was 
produced by the StringIO object you provided, when quopri tried to write the 
binary output that it produces to the object you handed it.

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[issue32268] quopri.decode(): string argument expected, got 'bytes'

[Alexey Luchko]

Alexey Luchko  added the comment:

Yes. With io.BytesIO() output, it works.

However, this kind of error messages is quite very confusing. It better be 
possible to distinguish binary and text streams, so one (including quopri 
module) could tell it won't work in advance %)

Thanks for referring to binascii module as well!

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[issue32268] quopri.decode(): string argument expected, got 'bytes'

[R. David Murray]

R. David Murray  added the comment:

Right, this is not a bug, it is working as documented.  You could submit an 
enhancement request, but I'm surprised to find that anyone is actually using 
that module :)

We unfortunately have multiple implementations of quoted printable handling in 
the stdlib.  You might be interested in the functions in the binascii module, 
which do accept unicode input when doing decoding.

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nosy: +r.david.murray
resolution:  -> not a bug
stage:  -> resolved
status: open -> closed
type:  -> behavior

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[issue32268] quopri.decode(): string argument expected, got 'bytes'

[Christoph Reiter]

Christoph Reiter  added the comment:

The documentation [0] states: "input and output must be binary file objects" 
and you are not passing a binary file object.

[0] https://docs.python.org/3.6/library/quopri.html#quopri.decode

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[issue32268] quopri.decode(): string argument expected, got 'bytes'

[Alexey Luchko]

New submission from Alexey Luchko :

$ python3 -c 'import io, quopri; quopri.decode(io.StringIO("some initial text 
data"), io.StringIO())'
Traceback (most recent call last):
  File "", line 1, in 
  File 
"/opt/local/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/quopri.py",
 line 125, in decode
output.write(odata)
TypeError: string argument expected, got 'bytes'

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components: Library (Lib)
messages: 307957
nosy: luch
priority: normal
severity: normal
status: open
title: quopri.decode(): string argument expected, got 'bytes'
versions: Python 3.6

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