Bug 841152 - readline breaks if we put a stream filter over sys.stdout
readline breaks if we put a stream filter over sys.stdout
Product: Fedora
Classification: Fedora
Component: python (Show other bugs)
Unspecified Unspecified
unspecified Severity unspecified
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Assigned To: Bohuslav "Slavek" Kabrda
Fedora Extras Quality Assurance
Depends On:
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Reported: 2012-07-18 05:44 EDT by Ales Kozumplik
Modified: 2015-02-17 09:21 EST (History)
6 users (show)

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Doc Type: Bug Fix
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Last Closed: 2015-02-17 09:21:26 EST
Type: Bug
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Attachments (Terms of Use)
simple program demonstrating the issue (640 bytes, text/plain)
2012-07-18 05:44 EDT, Ales Kozumplik
no flags Details

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Description Ales Kozumplik 2012-07-18 05:44:54 EDT
Created attachment 598838 [details]
simple program demonstrating the issue

In Yum/DNF a custom object is overriding sys.stdout. It's only job is to encode Unicode strings sent to output (e.g. via 'print') so yum doesn't die on UnicodeError when its output is redirected to a file.

I was wondering why cursor keys in pdb don't traverse the readline history as expected, it turns out assigning custom objects to sys.stdout silently disables readline. Attached is a trivial program demonstrating this.
Comment 1 Bohuslav "Slavek" Kabrda 2012-07-19 04:13:30 EDT
I would consider moving to Python 3 from Python 2. This problem doesn't appear in Python 3 (note that the function is not called "raw_input", but "input"). Also the unicode handling is much better in Python 3.
In the meantime, I will try to investigate this issue and come out with a solution for Python 2.
Comment 2 Bohuslav "Slavek" Kabrda 2012-07-20 04:54:11 EDT
It seems that the core of the problem is in function "builtin_raw_input" in file Python/bltinmodule.c - there are 2 checks that try to find out whether stdin and stdout are tty.
This in turn triggers some checks, whether type of stdout is types.FileType etc. So the only way I could think of is make UnicodeStream subclass of types.FileType. I however still can't find a way to properly redefine the methods/attributes in UnicodeStream and I keep getting
"ValueError: I/O operation on closed file"
no matter how I override the closed() or any other method/attribute. So no luck in this end.

Looking at Python 3 way, the logic of finding out whether stdout is a tty is completely rewritten [1] and I think that Python 2 version would need significant adjustments to work this way. Maybe Dave, who understands Python's C implementation much better, might be able to answer backporting this behaviour would be sane.

[1] http://hg.python.org/cpython/file/abc26b51fbfc/Python/bltinmodule.c#l1642
Comment 3 Fedora End Of Life 2013-04-03 10:38:18 EDT
This bug appears to have been reported against 'rawhide' during the Fedora 19 development cycle.
Changing version to '19'.

(As we did not run this process for some time, it could affect also pre-Fedora 19 development
cycle bugs. We are very sorry. It will help us with cleanup during Fedora 19 End Of Life. Thank you.)

More information and reason for this action is here:
Comment 4 Fedora Admin XMLRPC Client 2013-05-10 00:59:30 EDT
This package has changed ownership in the Fedora Package Database.  Reassigning to the new owner of this component.
Comment 5 Fedora Admin XMLRPC Client 2013-05-10 01:00:40 EDT
This package has changed ownership in the Fedora Package Database.  Reassigning to the new owner of this component.
Comment 7 Fedora End Of Life 2015-01-09 12:15:52 EST
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Comment 8 Fedora End Of Life 2015-02-17 09:21:26 EST
Fedora 19 changed to end-of-life (EOL) status on 2015-01-06. Fedora 19 is
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