New submission from Terry J. Reedy:
It appears that Idle was originally written to run on *nix after being launched
from a command-line console. Messages related to Idle code (warnings and
exceptions) are sent back to the console, while messages related to user code
go to the shell window. This makes Idle a hybrid text/gui application.
Later, Idle was ported to run on Windows with the pythonw.exe no-console
binary. When it is started normally for Windows, from anything but a console,
there is no console. This has caused problems when Idle tries to write to the
non-existent console. (I do not know the situation on modern Mac and *nix.)
(Even when a console does exist, it will usually get buried and messages may
not be seen.)
Example: The warning system, monkey patched in both PyShell.py and run.py and
documented in the former. (Edited quote from 3.3.)
# Override warnings module to write to warning_stream.
# Initialize to send IDLE internal warnings to the console.
# ScriptBinding.check_syntax() will temporarily redirect the stream
# to the shell window to display warnings when checking user's code.
warning_stream = sys.__stderr__ # Typically None, at least on Windows.
def idle_showwarning(...
...
if file is None:
file = warning_stream # Which may itself be None!!!
try:
file.write(... # AttributeError when file is still None
except OSError:
pass # if file (probably __stderr__) is invalid, skip warning.
The patch for #18081 also catches AttributeError as a bandage.
Issue goal: make Idle a true gui app by removing the dependence on a console,
which may not exist.
Proposed method: re-factor Idle startup to try to import tkinter first, rather
than last.
If this import fails, inform user with console message and/or the os-specific
means to gui apps to tell users 'I cannot start because ...'. I know this
exists on Windows because I have seen such messages. I presume same is true on
other systems.
If this import succeeds, setup traceback and warnings hooks to send internal
messages to a gui messagebox rather than (or possibly in addition to) a console
that may or may not be present. Or send the messages to the Shell window, but
marked somehow as internal. The warnings hook might be used after importing
non-Idle modules but before importing Idle modules, so startup is not bogged
down on debug builds by DeprecationWarnings from non-Idle modules
To be a good citizen for testing, all custom hooks should be undone before the
PyShell import finishes and before PyShell.main exits (same for run.py).
----------
messages: 191966
nosy: ned.deily, roger.serwy, terry.reedy
priority: normal
severity: normal
status: open
title: Idle: stop depending on console output
type: behavior
versions: Python 2.7, Python 3.3, Python 3.4
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Python tracker <rep...@bugs.python.org>
<http://bugs.python.org/issue18318>
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