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Title: input() doesn't catch _PyUnicode_AsString() exception; io.StringIO().encoding is None
Type: behavior Stage: resolved
Components: IO, Library (Lib) Versions: Python 3.7, Python 3.6, Python 3.5
Status: closed Resolution: fixed
Dependencies: 24402 Superseder:
Assigned To: Nosy List: aliles, amaury.forgeotdarc, belopolsky, dangyogi, erik.bray, flox, gruszczy, martin.panter, pitrou, r.david.murray, serhiy.storchaka, vstinner
Priority: normal Keywords: patch

Created on 2010-03-28 20:15 by dangyogi, last changed 2022-04-11 14:56 by admin. This issue is now closed.

File name Uploaded Description Edit dangyogi, 2010-03-28 20:15 small bug demo program
8256_3.patch gruszczy, 2010-03-30 20:35
input_stdout_encoding.patch vstinner, 2010-05-14 01:20
input_stdout_none_encoding.patch vstinner, 2011-11-03 20:25
p1345978092.diff aliles, 2012-08-26 10:59 review
input_fallback.patch serhiy.storchaka, 2015-10-06 19:09 review
Pull Requests
URL Status Linked Edit
PR 517 merged serhiy.storchaka, 2017-03-06 13:34
PR 640 closed serhiy.storchaka, 2017-03-12 11:55
PR 641 merged serhiy.storchaka, 2017-03-12 12:31
PR 642 merged serhiy.storchaka, 2017-03-12 12:41
PR 703 larry, 2017-03-17 21:00
Messages (32)
msg101874 - (view) Author: Bruce Frederiksen (dangyogi) Date: 2010-03-28 20:15
I'm getting a "TypeError: bad argument type for built-in operation" on a print() with no arguments.  This seems to be a problem in both 3.1 and 3.1.2 (haven't tried 3.1.1).

I've narrowed the problem down in a very small demo program that you can run to reproduce the bug.  Just do "python3.1" and hit <ENTER> at the "prompt:".

Removing the doctest call (and calling "foo" directly) doesn't get the error.  Also removing the "input" call (and leaving the doctest call in) doesn't get the error.

The startup banner on my python3.1 is:
Python 3.1.2 (r312:79147, Mar 26 2010, 16:55:44) 
[GCC 4.3.3] on linux2

I compiled python 3.1.2 with ./configure, make, make altinstall without any options.  I'm running ubuntu 9.04 with the 2.6.28-18-generic (32-bit) kernel.
msg101876 - (view) Author: Florent Xicluna (flox) * (Python committer) Date: 2010-03-28 22:46

There's something wrong around the doctest._SpoofOut class.
This script triggers the same bug (both 3.x and 3.1).


$ ./python 
Traceback (most recent call last):
  File "", line 13, in <module>
  File "", line 7, in foo
TypeError: bad argument type for built-in operation
msg101879 - (view) Author: Filip Gruszczyński (gruszczy) Date: 2010-03-28 22:59
The bug is triggered by input, not by print. The exact place is _PyUnicode_AsStringAndSize, where unicode check happens. Then print checks PyError_Occured and catches this error. Either this error should not be raised or should be cleared input finishes.

I'd love to provide a patch, but I have no idea, what should be corrected and how. If some would tutor me a little, I would be very happy to learn and code this.
msg101880 - (view) Author: Florent Xicluna (flox) * (Python committer) Date: 2010-03-28 23:01
Right. It does not involve doctest.

import io, sys

original_stdout = sys.stdout

    sys.stdout = io.StringIO()
    sys.stdout = original_stdout
msg101886 - (view) Author: Filip Gruszczyński (gruszczy) Date: 2010-03-29 12:20
The problem occurs in line in bltinmodule.c:

		po = PyUnicode_AsEncodedString(stringpo,
			_PyUnicode_AsString(stdout_encoding), NULL);

Where _PyUnicode_AsString returns NULL, since stdout_encoding is Py_None and that won't pass PyUnicode_Check in _PyUnicode_AsStringAndSize. To what object can _PyUnicode_AsString be turned and then passed to _PyUnicode_AsStringAndSize? Is there some default 'utf-8' encoding object?
msg101888 - (view) Author: R. David Murray (r.david.murray) * (Python committer) Date: 2010-03-29 13:05
Whatever the solution to this issue is, it certainly looks like a bug that the return value of that function isn't being checked for errors.
msg101900 - (view) Author: Filip Gruszczyński (gruszczy) Date: 2010-03-29 19:21
I have written a small patch, that solves the problem, but is disgusting. Could anyone tell me, how I can get some default encoding from Python internals (I have no idea where to look) and return it inside _PyUnicode_AsStringAndSize? Anyway, now when the error happens inside input, it raises an Exception properly. So now I only need to know, how to correct the bug in an elegant fashion.
msg101904 - (view) Author: Filip Gruszczyński (gruszczy) Date: 2010-03-29 20:56
Ok, I have found Py_FileDefaultSystemEncoding and use it, however I had to cast it to (char *), because it's a const char *. Maybe I could do it better?
msg101956 - (view) Author: Filip Gruszczyński (gruszczy) Date: 2010-03-30 20:35
I have read, that I shouldn't directly use Py_FileSystemDefaultEncoding and rather use PyUnicode_GetDefaultEncoding, so I have changed the code a little.
msg105422 - (view) Author: Filip Gruszczyński (gruszczy) Date: 2010-05-09 23:52
Bump! Is there anything happening about this bug? Is my patch any good or should I try to work on something different?
msg105435 - (view) Author: R. David Murray (r.david.murray) * (Python committer) Date: 2010-05-10 14:15
Victor, you've been dealing with Python's default encoding lately, care to render an opinion on the correct fix for this bug?

@Filip: the patch will need a unit test, which will also help with assessing the validity of the fix.
msg105436 - (view) Author: Filip Gruszczyński (gruszczy) Date: 2010-05-10 14:19
I'll try to code a small test this evening.
msg105439 - (view) Author: Amaury Forgeot d'Arc (amaury.forgeotdarc) * (Python committer) Date: 2010-05-10 14:54
The patch is wrong: _PyUnicode_AsString(Py_None) should not return "utf8"!

I suggest that since PyOS_Readline() write the prompt to stderr, the conversion uses the encoding of stderr.
msg105555 - (view) Author: Filip Gruszczyński (gruszczy) Date: 2010-05-11 22:37
Amaury, could you elaborate a little more on this? I am pretty new to all this and I would happily write the patch, if only you could give me some clue on how I should approach this.
msg105616 - (view) Author: STINNER Victor (vstinner) * (Python committer) Date: 2010-05-13 00:14
This issue is directly related to issue #6697. The first problem is that the builtin input() function doesn't check that _PyUnicode_AsString() result is not NULL.

The second problem is that io.StringIO().encoding is None. I don't understand why it is None whereas it uses utf8 (it calls TextIOWrapper constructor with encodings="utf8" and errors="strict").

I will be difficult to write an unit test because the issue only occurs if stdin and stdout are TTY: input() calls PyOS_Readline(stdin, stdout, prompt). 


@gruszczy: You're patch is just a workaround, not the right fix. The problem should be fixed in input(), not in PyUnicode methods. _PyUnicode_AsString() expects an unicode argument, it should raise an error if the argument is None (and not return a magical value).
msg105676 - (view) Author: STINNER Victor (vstinner) * (Python committer) Date: 2010-05-14 01:20
Here is a patch catching the _PyUnicode_AsString() error.

input() uses sys.stdout.encoding to encode the prompt to a byte string, but 
PyOS_StdioReadline() writes the prompt to stderr (it should use sys_stdout).

I don't know which encoding should be used if sys.stdout.encoding is None (eg. 
if sys.stdout is a StringIO() object).

StringIO() of _io module has no encoding because it stores unicode characters, 
not bytes. StringIO() of _pyio module is based on BytesIO() and use utf8 
encoding, but the reference implementation is now _io.
msg105699 - (view) Author: Amaury Forgeot d'Arc (amaury.forgeotdarc) * (Python committer) Date: 2010-05-14 11:21
since the prompt is written to stderr, why is sys.stdout.encoding used instead of sys.stderr.encoding?
msg105700 - (view) Author: STINNER Victor (vstinner) * (Python committer) Date: 2010-05-14 11:31
amaury> since the prompt is written to stderr, why is sys.stdout.encoding
amaury> used instead of sys.stderr.encoding?

input() calls PyOS_Readline() but PyOS_Readline() has multiple 
 - PyOS_StdioReadline() if sys_stdin or sys_stdout is not a TTY
 - or PyOS_ReadlineFunctionPointer callback:
   - vms__StdioReadline() (VMS only)
   - PyOS_StdioReadline()
   - call_readline() when readline module is loaded

call_readline() calls rl_callback_handler_install() with the prompt which 
writes the prompt to *stdout* (try ./python 2>/dev/null).

I don't think that it really matters that the prompt is written to stderr with 
stdout encoding, because both outputs always use the same encoding.
msg146590 - (view) Author: Florent Xicluna (flox) * (Python committer) Date: 2011-10-29 02:04
Confirmed in 3.3.
The patch does not apply cleanly on trunk.
msg146969 - (view) Author: STINNER Victor (vstinner) * (Python committer) Date: 2011-11-03 20:07
A patch similar to input_stdout_encoding.patch has been applied to 3.2 and 3.3 for the issue #6697: see changeset 846866aa0eb6.
msg146973 - (view) Author: STINNER Victor (vstinner) * (Python committer) Date: 2011-11-03 20:25
input_stdout_none_encoding.patch uses UTF-8 if sys.stdout.encoding is None.
msg168873 - (view) Author: Aaron Iles (aliles) * Date: 2012-08-22 12:01
Replicated this issue on Python 3.3b2. The cause is the 'encoding' and 'errors' attributes on io.StringIO() being None. Doctest replaces sys.stdout with a StringIO subclass. The exception raised is still a TypeError.

At this point I'm unsure what the fix should be:

1. Should the exception raised be more descriptive of the problem?
2. Should io.StringIO have real values for encoding and errors?
3. Should Doctest's StingIO class provide encoding and errors?
msg168880 - (view) Author: Antoine Pitrou (pitrou) * (Python committer) Date: 2012-08-22 12:48
> I suggest that since PyOS_Readline() write the prompt to stderr, the
> conversion uses the encoding of stderr.

Agreed with Amaury.
msg169166 - (view) Author: Aaron Iles (aliles) * Date: 2012-08-26 10:59
Upload new patch that uses encoding and errors from stderr if stdout values are invalid unicode. Includes unit test in

With this patch I am no longer able to replicate this issue.
msg252421 - (view) Author: Serhiy Storchaka (serhiy.storchaka) * (Python committer) Date: 2015-10-06 18:28
I would fallback to PyFile_WriteObject(prompt, fout, Py_PRINT_RAW) if the stdout has no the encoding attribute or it is not a string.
msg252422 - (view) Author: Serhiy Storchaka (serhiy.storchaka) * (Python committer) Date: 2015-10-06 19:09
Here is a patch.
msg252437 - (view) Author: Martin Panter (martin.panter) * (Python committer) Date: 2015-10-06 23:04
Serhiy, your patch looks like a worthwhile improvement because it adds proper error checking and handling. However I suspect this original bug is actually a side effect of Issue 24402. The code in question shouldn’t even be running, because sys.stdout is not the original output file descriptor, and is not a terminal.
msg255217 - (view) Author: Erik Bray (erik.bray) * (Python triager) Date: 2015-11-23 20:17
I just recently discovered this myself.  In the process of debugging the issue I also noticed the same bug that is now fixed via Issue 24402.

While I agree that Issue 24402 mostly mitigates the issue I think this patch is still worthwhile, as the current behavior still leads to cryptic, hard to debug errors.  For example (although this is not great code, bear with me...) one could write a stdout wrapper like:

>>> class WrappedStream:
...     encoding = 'utf8'
...     errors = None
...     def __getattr__(self, attr):
...         return getattr(sys.__stdout__, attr)
>>> sys.stdout = WrappedStream()
>>> sys.stdout.fileno()
>>> sys.stdout.isatty()
>>> sys.stdout.errors
>>> input('Prompt: ')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: bad argument type for built-in operation

This still goes down the path for ttys, but because the 'errors' attribute does not defer to the underlying stream it still leads to a hard to debug exception.  To be clear, I think the above code *should* break, just not as cryptically.
msg255220 - (view) Author: Erik Bray (erik.bray) * (Python triager) Date: 2015-11-23 20:25
> I think the above code *should* break

Actually, I see now that Serhiy's patch would allow this example to just pass through to the non-interactive fallback.  So I take it back that my example should break--I think using the fallback would also be fine.
msg290194 - (view) Author: Serhiy Storchaka (serhiy.storchaka) * (Python committer) Date: 2017-03-24 22:21
New changeset a16894ebf8823f0e09036aacde9288c00e8d9058 by Serhiy Storchaka in branch '3.5':
[3.5] bpo-8256: Fixed possible failing or crashing input() (#642)
msg290195 - (view) Author: Serhiy Storchaka (serhiy.storchaka) * (Python committer) Date: 2017-03-24 22:21
New changeset aac875fa2f03cab61ceeaa2621c4c5534c7bcfc2 by Serhiy Storchaka in branch '3.6':
[3.6] bpo-8256: Fixed possible failing or crashing input() (#641)
msg290200 - (view) Author: Serhiy Storchaka (serhiy.storchaka) * (Python committer) Date: 2017-03-24 22:23
New changeset c2cf12857187aa147c268651f10acd6da2c9cb74 by Serhiy Storchaka in branch 'master':
bpo-8256: Fixed possible failing or crashing input() (#517)
Date User Action Args
2022-04-11 14:56:59adminsetgithub: 52503
2017-03-24 22:23:04serhiy.storchakasetmessages: + msg290200
2017-03-24 22:21:44serhiy.storchakasetmessages: + msg290195
2017-03-24 22:21:37serhiy.storchakasetmessages: + msg290194
2017-03-17 21:11:46serhiy.storchakasetstatus: open -> closed
resolution: fixed
stage: patch review -> resolved
2017-03-17 21:00:31larrysetpull_requests: + pull_request577
2017-03-12 12:41:28serhiy.storchakasetpull_requests: + pull_request531
2017-03-12 12:31:34serhiy.storchakasetpull_requests: + pull_request530
2017-03-12 11:55:48serhiy.storchakasetpull_requests: + pull_request529
2017-03-06 13:34:57serhiy.storchakasetpull_requests: + pull_request427
2017-03-06 13:33:37serhiy.storchakasetversions: + Python 3.7, - Python 3.4
2015-11-23 20:25:16erik.braysetmessages: + msg255220
2015-11-23 20:17:46erik.braysetnosy: + erik.bray
messages: + msg255217
2015-10-06 23:04:35martin.pantersetnosy: + martin.panter
dependencies: + input() uses sys.__stdout__ instead of sys.stdout for prompt
messages: + msg252437
2015-10-06 19:09:04serhiy.storchakasetfiles: + input_fallback.patch

messages: + msg252422
stage: needs patch -> patch review
2015-10-06 18:28:21serhiy.storchakasetnosy: + serhiy.storchaka

messages: + msg252421
versions: + Python 3.4, Python 3.5, Python 3.6, - Python 3.2, Python 3.3
2012-08-26 10:59:20alilessetfiles: + p1345978092.diff

messages: + msg169166
2012-08-22 12:48:34pitrousetnosy: + pitrou
messages: + msg168880
2012-08-22 12:01:33alilessetnosy: + aliles
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2011-11-03 20:25:56vstinnersetfiles: + input_stdout_none_encoding.patch

messages: + msg146973
2011-11-03 20:07:08vstinnersetmessages: + msg146969
2011-10-29 02:04:40floxsetstage: test needed -> needs patch
messages: + msg146590
versions: + Python 3.3, - Python 3.1
2010-05-14 11:31:06vstinnersetmessages: + msg105700
2010-05-14 11:21:10amaury.forgeotdarcsetmessages: + msg105699
2010-05-14 01:20:13vstinnersetfiles: + input_stdout_encoding.patch

messages: + msg105676
2010-05-13 00:15:14vstinnersettitle: TypeError: bad argument type for built-in operation -> input() doesn't catch _PyUnicode_AsString() exception; io.StringIO().encoding is None
2010-05-13 00:14:24vstinnersetmessages: + msg105616
2010-05-11 22:37:11gruszczysetmessages: + msg105555
2010-05-11 15:44:19belopolskysetnosy: + belopolsky
2010-05-10 14:54:22amaury.forgeotdarcsetnosy: + amaury.forgeotdarc
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2010-05-10 14:19:14gruszczysetmessages: + msg105436
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2010-05-09 23:52:19gruszczysetmessages: + msg105422
2010-03-30 20:35:48gruszczysetfiles: - 8256_2.patch
2010-03-30 20:35:44gruszczysetfiles: - 8256_1.patch
2010-03-30 20:35:31gruszczysetfiles: + 8256_3.patch

messages: + msg101956
2010-03-29 20:56:03gruszczysetfiles: + 8256_2.patch

messages: + msg101904
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2010-03-29 13:05:35r.david.murraysetnosy: + r.david.murray
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2010-03-29 12:20:59gruszczysetmessages: + msg101886
2010-03-28 23:01:53floxsetmessages: + msg101880
2010-03-28 22:59:36floxsetfiles: -
2010-03-28 22:59:10gruszczysetnosy: + gruszczy
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2010-03-28 22:46:01floxsetfiles: +
priority: normal

components: - Interpreter Core
versions: + Python 3.2
nosy: + flox

messages: + msg101876
stage: test needed
2010-03-28 20:15:14dangyogicreate