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bpo-39712: Cross reference env. vars and -X command line options #18685

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17 changes: 11 additions & 6 deletions Doc/using/cmdline.rst
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Expand Up @@ -430,15 +430,17 @@ Miscellaneous options
Reserved for various implementation-specific options. CPython currently
defines the following possible values:

* ``-X faulthandler`` to enable :mod:`faulthandler`;
* ``-X faulthandler`` to enable :mod:`faulthandler`. See also
:envvar:`PYTHONFAULTHANDLER`.
* ``-X showrefcount`` to output the total reference count and number of used
memory blocks when the program finishes or after each statement in the
interactive interpreter. This only works on debug builds.
* ``-X tracemalloc`` to start tracing Python memory allocations using the
:mod:`tracemalloc` module. By default, only the most recent frame is
stored in a traceback of a trace. Use ``-X tracemalloc=NFRAME`` to start
tracing with a traceback limit of *NFRAME* frames. See the
:func:`tracemalloc.start` for more information.
tracing with a traceback limit of *NFRAME* frames. See
:func:`tracemalloc.start` and :envvar:`PYTHONTRACEMALLOC` for more
information.
* ``-X importtime`` to show how long each import takes. It shows module
name, cumulative time (including nested imports) and self time (excluding
nested imports). Note that its output may be broken in multi-threaded
Expand All @@ -450,6 +452,7 @@ Miscellaneous options
* ``-X utf8`` enables the :ref:`Python UTF-8 Mode <utf8-mode>`.
``-X utf8=0`` explicitly disables :ref:`Python UTF-8 Mode <utf8-mode>`
(even when it would otherwise activate automatically).
See also :envvar:`PYTHONUTF8`.
* ``-X pycache_prefix=PATH`` enables writing ``.pyc`` files to a parallel
tree rooted at the given directory instead of to the code tree. See also
:envvar:`PYTHONPYCACHEPREFIX`.
Expand Down Expand Up @@ -738,16 +741,17 @@ conflict.
Python memory allocations using the :mod:`tracemalloc` module. The value of
the variable is the maximum number of frames stored in a traceback of a
trace. For example, ``PYTHONTRACEMALLOC=1`` stores only the most recent
frame. See the :func:`tracemalloc.start` for more information.
frame. See the :func:`tracemalloc.start` for more information. This is
equivalent to setting the :option:`-X` ``tracemalloc`` option.

.. versionadded:: 3.4


.. envvar:: PYTHONPROFILEIMPORTTIME

If this environment variable is set to a non-empty string, Python will
show how long each import takes. This is exactly equivalent to setting
``-X importtime`` on the command line.
show how long each import takes. This is equivalent to setting the
:option:`-X` ``importtime`` option.

.. versionadded:: 3.7

Expand Down Expand Up @@ -893,6 +897,7 @@ conflict.
If this environment variable is set to a non-empty string, enable
:ref:`Python Development Mode <devmode>`, introducing additional runtime
checks that are too expensive to be enabled by default.
This is equivalent to setting the :option:`-X` ``dev`` option.

.. versionadded:: 3.7

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