All modules created using multi-phase initialization are expected to support:ref:`sub-interpreters<sub-interpreter-support>` and multiple:c:func:`Py_Initialize`/:c:func:`Py_Finalize` cycles correctly.Typically, extensions ensure this in one of these ways:

Modules created using multi-phase initialization are expected to handlesub-interpreters in either of the following two ways:* either they fully support multiple interpreters by:ref:`isolating module instances<isolating-extensions-howto>`;* or they signal that multiple interpreters are not supported by:ref:`raising an error on repeated initialization<isolating-extensions-optout>`  and/or limiting a module to the main interpreter using:c:data:`Py_mod_multiple_interpreters`.This way, users will not encounter crashes or undefined behavior whentrying to use these modules from multiple interpreters.

Multi-phase initialization allows creating multiple independent instances of themodule object.Extensions are expected to handle this in one of the following ways:* either by:ref:`isolating module instances<isolating-extensions-howto>`;* and/or by:ref:`raising an error on repeated initialization<isolating-extensions-optout>`;* and/or limiting a module to the main interpreter using:c:data:`Py_mod_multiple_interpreters`.This way, users will not encounter crashes or undefined behavior whentrying to use these modules from:ref:`sub-interpreters<sub-interpreter-support>`.The first two ways also prevent crashes when reusing the module afterPython runtime reinitialization (:c:func:`Py_Finalize` and:c:func:`Py_Initialize`)and reimporting a module after it is removed from:py:attr:`sys.modules`.

When using per-module state, module instances should be:ref:`isolated<isolating-extensions-howto>` to ensure that they are free of unwantedside-effects. If the module still uses global state, or it otherwise has notyet been isolated, either or both of of the following two options should be used:*:ref:`raising an error on repeated initialization<isolating-extensions-optout>`* limiting a module to the main interpreter using:c:data:`Py_mod_multiple_interpreters`.This way, users will not encounter crashes or undefined behavior whentrying to use these modules from:ref:`sub-interpreters<sub-interpreter-support>`.Ensuring a module is properly isolated or raising an explicit error also preventcrashes when reusing the module after Python runtime reinitialization(:c:func:`Py_Finalize` and:c:func:`Py_Initialize`) or reimporting a module afterit has been removed from:py:attr:`sys.modules`.

When using per-module state, module instances should be:ref:`isolated<isolating-extensions-howto>` to ensure that they are free of unwantedside-effects. If the module still uses global state, or it otherwise has notyet been isolated, either or both of of the following two options should be used:*:ref:`raising an error on repeated initialization<isolating-extensions-optout>`* limiting a module to the main interpreter using:c:data:`Py_mod_multiple_interpreters`.This way, users will not encounter crashes or undefined behavior whentrying to use these modules from:ref:`sub-interpreters<sub-interpreter-support>`.Ensuring a module is properly isolated or raising an explicit error also preventcrashes when reusing the module after Python runtime reinitialization(:c:func:`Py_Finalize` and:c:func:`Py_Initialize`) or reimporting a module afterit has been removed from:py:attr:`sys.modules`.