Python interactive console doesn't use sys.stdin for input

[Drekin]

BPO	17620
Nosy	@gvanrossum, @birkenfeld, @pfmoore, @ncoghlan, @pitrou, @benjaminp, @merwok, @zooba

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2013-04-02.16:59:14.835>
labels = ['type-feature', '3.8', '3.9', '3.10']
title = "Python interactive console doesn't use sys.stdin for input"
updated_at = <Date 2021-03-15.21:01:39.375>
user = 'https://bugs.python.org/Drekin'

bugs.python.org fields:

activity = <Date 2021-03-15.21:01:39.375>
actor = 'eryksun'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = []
creation = <Date 2013-04-02.16:59:14.835>
creator = 'Drekin'
dependencies = []
files = []
hgrepos = []
issue_num = 17620
keywords = []
message_count = 29.0
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nosy_count = 10.0
nosy_names = ['gvanrossum', 'georg.brandl', 'paul.moore', 'ncoghlan', 'pitrou', 'benjamin.peterson', 'eric.araujo', 'tshepang', 'Drekin', 'steve.dower']
pr_nums = []
priority = 'normal'
resolution = None
stage = 'needs patch'
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue17620'
versions = ['Python 3.8', 'Python 3.9', 'Python 3.10']

[Drekin]

The Python interactive console actually doesn't use sys.stdin but standard C stdin for input. Is there any reason for this? Why it then uses its encoding attribute? (Assigning sys.stdin something, that doesn't have encoding attribute freezes the interpreter.) If anything, wouldn't it make more sense if it used sys.__stdin__.encoding instead of sys.stdin? sys.stdin is intended to be set by user (it affects input() and code.inpterrupt() which tries to minic standard interactive console).

[Drekin]

Sorry for typos.
• interactive console doesn't use sys.stdin for input, why?
• it uses sys.stdin.encoding, shouldn't it rather use sys.__stdin__.encoding if anything?
• input() and hence code.interact() uses sys.stdin

[pitrou]

• interactive console doesn't use sys.stdin for input, why?

Modules/main.c calls PyRun_AnyFileFlags(stdin, "<stdin>", ...). At this point, sys.stdin *is* the same as C stdin by construction, so I'm not sure how you came to encounter the issue.

However, it's also true that if you later redirect sys.stdin, it will be ignored and the original C stdin (as passed to PyRun_InteractiveLoopFlags) will continue to be used. On the other hand, the input() implementation has dedicated logic to find out whether sys.stdin is the same as C stdin.

(by the way, the issue should also apply to 2.7)

• it uses sys.stdin.encoding, shouldn't it rather use sys.__stdin__.encoding if anything?

Assuming the previous bug gets fixed, then no :-)

[Drekin]

I encountered it when I changed sys.stdin at runtime (I thought it was a supported feature) to affect the interactive console, see http://bugs.python.org/issue1602 .

[pitrou]

Ok, I guess it would need a new API (PyRun_Stdio()?) to run the interactive loop from sys.stdin, rather than from a fixed FILE*.

[Drekin]

Is there any chance the API will be added and used by python.exe?

[ncoghlan]

Steve, another one to look at in the context of improving the Unicode handling situation at the Windows command prompt.

[zooba]

Thanks Nick, but this has a pretty clear scope that may help the Unicode situation in cmd but doesn't directly relate to it.

[Drekin]

There is still the serious inconsistency that the sys.stdin is not used for input by interactive loop but its encoding is. So if I replace sys.stdin with a custom object with its own encoding attribute, the standard interactive loop tries to use this encoding which may result in an exception on any input.

[gvanrossum]

Is this at all related to the use of GNU readline?