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gh-142474: Clarify -i interaction with PYTHONSTARTUP #142502

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12 changes: 9 additions & 3 deletions Doc/using/cmdline.rst
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Expand Up @@ -302,16 +302,22 @@ Miscellaneous options

.. option:: -i

Enter interactive mode after execution.
Enter interactive mode after execution, or force interactive mode even when
:data:`sys.stdin` does not appear to be a terminal.
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@FFY00 FFY00 Dec 10, 2025

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I would probably rewrite it as it is worded in python --help.

forces a prompt even if stdin does not appear to be a terminal

Saying "interactive" is not quite correct, "prompt" better describes it.


Using the :option:`-i` option will enter interactive mode in any of the following circumstances\:

* When a script is passed as first argument
* When the :option:`-c` option is used
* When the :option:`-m` option is used

Interactive mode will start even when :data:`sys.stdin` does not appear to be a terminal. The
:envvar:`PYTHONSTARTUP` file is not read.
In these "execute then interact" cases, Python runs the script or command
first and does not read the :envvar:`PYTHONSTARTUP` file before entering
interactive mode.

When :option:`-i` is used only to force interactive mode despite redirected
standard input (for example, ``python -i < /dev/null``), the interpreter
enters interactive mode directly and reads :envvar:`PYTHONSTARTUP` as usual.

This can be useful to inspect global variables or a stack trace when a script
raises an exception. See also :envvar:`PYTHONINSPECT`.
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