Module Objects

single: ModuleType (in module types)

This instance of PyTypeObject represents the Python module type. This is exposed to Python programs as types.ModuleType.

Return true if p is a module object, or a subtype of a module object. This function always succeeds.

Return true if p is a module object, but not a subtype of PyModule_Type. This function always succeeds.

single: __name__ (module attribute) single: __doc__ (module attribute) single: __file__ (module attribute) single: __package__ (module attribute) single: __loader__ (module attribute)

Return a new module object with module.__name__ set to name. The module's !__name__, ~module.__doc__, ~module.__package__ and ~module.__loader__ attributes are filled in (all but !__name__ are set to None). The caller is responsible for setting a ~module.__file__ attribute.

Return NULL with an exception set on error.

3.3

3.4 ~module.__package__ and ~module.__loader__ are now set to None.

Similar to PyModule_NewObject, but the name is a UTF-8 encoded string instead of a Unicode object.

single: __dict__ (module attribute)

Return the dictionary object that implements module's namespace; this object is the same as the ~object.__dict__ attribute of the module object. If module is not a module object (or a subtype of a module object), SystemError is raised and NULL is returned.

It is recommended extensions use other PyModule_* and PyObject_* functions rather than directly manipulate a module's ~object.__dict__.

The returned reference is borrowed from the module; it is valid until the module is destroyed.

single: __name__ (module attribute) single: SystemError (built-in exception)

Return module's ~module.__name__ value. If the module does not provide one, or if it is not a string, SystemError is raised and NULL is returned.

3.3

Similar to PyModule_GetNameObject but return the name encoded to 'utf-8'.

The returned buffer is only valid until the module is renamed or destroyed. Note that Python code may rename a module by setting its ~module.__name__ attribute.

Return a pointer to the PyModuleDef struct from which the module was created, or NULL if the module wasn't created from a definition.

On error, return NULL with an exception set. Use PyErr_Occurred to tell this case apart from a missing !PyModuleDef.

single: __file__ (module attribute) single: SystemError (built-in exception)

Return the name of the file from which module was loaded using module's ~module.__file__ attribute. If this is not defined, or if it is not a string, raise SystemError and return NULL; otherwise return a reference to a Unicode object.

3.2

Similar to PyModule_GetFilenameObject but return the filename encoded to 'utf-8'.

The returned buffer is only valid until the module's ~module.__file__ attribute is reassigned or the module is destroyed.

PyModule_GetFilename raises UnicodeEncodeError on unencodable filenames, use PyModule_GetFilenameObject instead.

Module definition

Modules created using the C API are typically defined using an array of PySlot structs, which provides a "description" of how a module should be created. See capi-slots for more information on slots in general.

The slots array is usually used to define an extension module's “main” module object (see extension-modules for details). It can also be used to create extension modules dynamically <module-from-slots>.

Unless specified otherwise, the same slot ID may not be repeated in an array of slots.

Metadata slots

Slot ID <PySlot.sl_id> for the name of the new module, as a NUL-terminated UTF8-encoded const char *.

Note that modules are typically created using a ~importlib.machinery.ModuleSpec, and when they are, the name from the spec will be used instead of !Py_mod_name. However, it is still recommended to include this slot for introspection and debugging purposes.

3.15

Use PyModuleDef.m_name instead to support previous versions.

Slot ID <PySlot.sl_id> for the docstring of the new module, as a NUL-terminated UTF8-encoded const char *.

Usually it is set to a variable created with PyDoc_STRVAR.

3.15

Use PyModuleDef.m_doc instead to support previous versions.

Feature slots

Slot ID <PySlot.sl_id> whose value points to a PyABIInfo structure describing the ABI that the extension is using.

A suitable !PyABIInfo variable can be defined using the PyABIInfo_VAR macro, as in:

PyABIInfo_VAR(abi_info);

static PySlot mymodule_slots[] = {
   PySlot_DATA(Py_mod_abi, &abi_info),
   ...
};

When creating a module, Python checks the value of this slot using PyABIInfo_Check.

This slot is required, except for modules created from PyModuleDef.

3.15

Slot ID <PySlot.sl_id> whose value is one of:

The module does not support being imported in subinterpreters.

The module supports being imported in subinterpreters, but only when they share the main interpreter's GIL. (See isolating-extensions-howto.)

The module supports being imported in subinterpreters, even when they have their own GIL. (See isolating-extensions-howto.)

This slot determines whether or not importing this module in a subinterpreter will fail.

If Py_mod_multiple_interpreters is not specified, the import machinery defaults to Py_MOD_MULTIPLE_INTERPRETERS_SUPPORTED.

For historical reasons, the values are declared as pointers (void *). When using PySlot arrays, use PySlot_DATA for !Py_mod_multiple_interpreters:

PySlot_DATA(Py_mod_multiple_interpreters,
            Py_MOD_PER_INTERPRETER_GIL_SUPPORTED)

3.12

Slot ID <PySlot.sl_id> whose value is one of:

The module depends on the presence of the global interpreter lock (GIL), and may access global state without synchronization.

The module is safe to run without an active GIL.

This slot is ignored by Python builds not configured with --disable-gil. Otherwise, it determines whether or not importing this module will cause the GIL to be automatically enabled. See whatsnew313-free-threaded-cpython for more detail.

If Py_mod_gil is not specified, the import machinery defaults to Py_MOD_GIL_USED.

For historical reasons, the values are declared as pointers (void *). When using PySlot arrays, use PySlot_DATA for !Py_mod_gil:

PySlot_DATA(Py_mod_gil, Py_MOD_GIL_NOT_USED)

3.13

Creation and initialization slots

Slot ID <PySlot.sl_id> for a function that creates the module object itself. The function must have the signature:

The function will be called with:

• spec: a ModuleSpec-like object, meaning that any attributes defined for importlib.machinery.ModuleSpec have matching semantics. However, any of the attributes may be missing.
• def: NULL, or the module definition if the module is created from one.

The function should return a new module object, or set an error and return NULL.

This function should be kept minimal. In particular, it should not call arbitrary Python code, as trying to import the same module again may result in an infinite loop.

If Py_mod_create is not specified, the import machinery will create a normal module object using PyModule_New. The name is taken from spec, not the definition, to allow extension modules to dynamically adjust to their place in the module hierarchy and be imported under different names through symlinks, all while sharing a single module definition.

There is no requirement for the returned object to be an instance of PyModule_Type. However, some slots may only be used with !PyModule_Type instances; in particular:

• Py_mod_exec,
• module state slots <ext-module-state-slots> (Py_mod_state_*),
• Py_mod_token.

3.5

3.15

The slots argument may be a ModuleSpec-like object, rather than a true ~importlib.machinery.ModuleSpec instance. Note that previous versions of CPython did not enforce this.

The def argument may now be NULL, since modules are not necessarily made from definitions.

Slot ID <PySlot.sl_id> for a function that will execute, or initialize, the module. This function does the equivalent to executing the code of a Python module: typically, it adds classes and constants to the module. The signature of the function is:

See the capi-module-support-functions section for some useful functions to call.

For backwards compatibility, the PyModuleDef.m_slots array may contain multiple !Py_mod_exec slots; these are processed in the order they appear in the array. Elsewhere (that is, in arguments to PyModule_FromSlotsAndSpec and in return values of PyModExport_{<name>}), repeating the slot is not allowed.

3.5

3.15

Repeated Py_mod_exec slots are disallowed, except in PyModuleDef.m_slots.

Slot ID <PySlot.sl_id> for a table of module-level functions, as an array of PyMethodDef values suitable as the functions argument to PyModule_AddFunctions.

Like other slot IDs, a slots array may only contain one !Py_mod_methods entry. To add functions from multiple PyMethodDef arrays, call PyModule_AddFunctions in the Py_mod_exec function.

The table must be statically allocated (or otherwise guaranteed to outlive the module object).

3.15

Use PyModuleDef.m_methods instead to support previous versions.

Module state

Extension modules can have module state -- a piece of memory that is allocated on module creation, and freed when the module object is deallocated. The module state is specified using dedicated slots <ext-module-state-slots>.

A typical use of module state is storing an exception type -- or indeed any type object defined by the module --

Unlike the module's Python attributes, Python code cannot replace or delete data stored in module state.

Keeping per-module information in attributes and module state, rather than in static globals, makes module objects isolated and safer for use in multiple sub-interpreters. It also helps Python do an orderly clean-up when it shuts down.

Extensions that keep references to Python objects as part of module state must implement Py_mod_state_traverse and Py_mod_state_clear functions to avoid reference leaks.

To retrieve the state from a given module, use the following functions:

Return the "state" of the module, that is, a pointer to the block of memory allocated at module creation time, or NULL. See Py_mod_state_size.

On error, return NULL with an exception set. Use PyErr_Occurred to tell this case apart from missing module state.

Set *result to the size of module's state, as specified using Py_mod_state_size (or PyModuleDef.m_size), and return 0.

On error, set *result to -1, and return -1 with an exception set.

3.15

Slots for defining module state

The following slot IDs <PySlot.sl_id> are available for defining the module state.

Slot ID <PySlot.sl_id> for the size of the module state, in bytes.

Setting the value to a non-negative value means that the module can be re-initialized and specifies the additional amount of memory it requires for its state.

See PEP 3121 for more details.

Use PyModule_GetStateSize to retrieve the size of a given module.

3.15

Use PyModuleDef.m_size instead to support previous versions.

Slot ID <PySlot.sl_id> for a traversal function to call during GC traversal of the module object.

The signature of the function, and meanings of the arguments, is similar as for PyTypeObject.tp_traverse:

This function is not called if the module state was requested but is not allocated yet. This is the case immediately after the module is created and before the module is executed (Py_mod_exec function). More precisely, this function is not called if the state size (Py_mod_state_size) is greater than 0 and the module state (as returned by PyModule_GetState) is NULL.

3.15

Use PyModuleDef.m_traverse instead to support previous versions.

Slot ID <PySlot.sl_id> for a clear function to call during GC clearing of the module object.

The signature of the function is:

This function is not called if the module state was requested but is not allocated yet. This is the case immediately after the module is created and before the module is executed (Py_mod_exec function). More precisely, this function is not called if the state size (Py_mod_state_size) is greater than 0 and the module state (as returned by PyModule_GetState) is NULL.

Like PyTypeObject.tp_clear, this function is not always called before a module is deallocated. For example, when reference counting is enough to determine that an object is no longer used, the cyclic garbage collector is not involved and the Py_mod_state_free function is called directly.

3.15

Use PyModuleDef.m_clear instead to support previous versions.

Slot ID <PySlot.sl_id> for a function to call during deallocation of the module object.

The signature of the function is:

This function is not called if the module state was requested but is not allocated yet. This is the case immediately after the module is created and before the module is executed (Py_mod_exec function). More precisely, this function is not called if the state size (Py_mod_state_size) is greater than 0 and the module state (as returned by PyModule_GetState) is NULL.

3.15

Use PyModuleDef.m_free instead to support previous versions.

Module token

Each module may have an associated token: a pointer-sized value intended to identify of the module state's memory layout. This means that if you have a module object, but you are not sure if it “belongs” to your extension, you can check using code like this:

PyObject *module = <the module in question>

void *module_token;
if (PyModule_GetToken(module, &module_token) < 0) {
    return NULL;
}
if (module_token != your_token) {
    PyErr_SetString(PyExc_ValueError, "unexpected module")
    return NULL;
}

// This module's state has the expected memory layout; it's safe to cast
struct my_state state = (struct my_state*)PyModule_GetState(module)

A module's token -- and the your_token value to use in the above code -- is:

• For modules created with PyModuleDef: the address of that PyModuleDef;
• For modules defined with the Py_mod_token slot: the value of that slot;
• For modules created from an PyModExport_* export hook <extension-export-hook>: the slots array that the export hook returned (unless overridden with Py_mod_token).

Slot ID <PySlot.sl_id> for the module token.

If you use this slot to set the module token (rather than rely on the default), you must ensure that:

• The pointer outlives the class, so it's not reused for something else while the class exists.
• It "belongs" to the extension module where the class lives, so it will not clash with other extensions.
• If the token points to a PyModuleDef struct, the module should behave as if it was created from that PyModuleDef. In particular, the module state must have matching layout and semantics.

Modules created from PyModuleDef always use the address of the PyModuleDef as the token. This means that !Py_mod_token cannot be used in PyModuleDef.m_slots.

3.15

Set *result to the module token for module and return 0.

On error, set *result to NULL, and return -1 with an exception set.

3.15

See also PyType_GetModuleByToken.

Creating extension modules dynamically

The following functions may be used to create an extension module dynamically, rather than from an extension's export hook <extension-export-hook>.

Create a new module object, given an array of slots <pymoduledef_slot> and the ~importlib.machinery.ModuleSpec spec.

The slots argument must point to an array of PySlot structures, terminated by an entry with slot ID of 0 (typically written as PySlot_END). The array must include a Py_mod_abi entry.

The spec argument may be any ModuleSpec-like object, as described in Py_mod_create documentation. Currently, the spec must have a name attribute.

On success, return the new module. On error, return NULL with an exception set.

Note that this does not process the module's execution slot (Py_mod_exec). Both !PyModule_FromSlotsAndSpec and PyModule_Exec must be called to fully initialize a module. (See also multi-phase-initialization.)

3.15

Execute the Py_mod_exec slot(s) of module.

On success, return 0. On error, return -1 with an exception set.

For clarity: If module has no slots, for example if it uses legacy single-phase initialization <single-phase-initialization>, this function does nothing and returns 0.

3.15

Module definition struct

Traditionally, extension modules were defined using a module definition as the “description" of how a module should be created. Rather than using an array of slots <pymoduledef_slot> directly, the definition has dedicated members for most common functionality, and allows additional slots as an extension mechanism.

This way of defining modules is still available and there are no plans to remove it.

The module definition struct, which holds information needed to create a module object.

This structure must be statically allocated (or be otherwise guaranteed to be valid while any modules created from it exist). Usually, there is only one variable of this type for each extension module defined this way.

The struct, including all members, is part of the Stable ABI <stable-abi> for non-free-threaded builds (abi3). In the Stable ABI for free-threaded builds (abi3t), this struct is opaque, and unusable in practice; see pymoduledef_slot for a replacement.

Always initialize this member to PyModuleDef_HEAD_INIT:

The type of !PyModuleDef.m_base.

The struct is part of the Stable ABI <stable-abi> for non-free-threaded builds (abi3). In the Stable ABI for Free-Threaded Builds (abi3t), this struct is opaque, and unusable in practice.

The required initial value for !PyModuleDef.m_base.

Corresponds to the Py_mod_name slot.

These members correspond to the Py_mod_doc slot. Setting this to NULL is equivalent to omitting the slot.

Corresponds to the Py_mod_state_size slot. Setting this to zero is equivalent to omitting the slot.

When using legacy single-phase initialization <single-phase-initialization> or when creating modules dynamically using PyModule_Create or PyModule_Create2, !m_size may be set to -1. This indicates that the module does not support sub-interpreters, because it has global state.

Corresponds to the Py_mod_methods slot. Setting this to NULL is equivalent to omitting the slot.

An array of additional slots, terminated by a {0, NULL} entry. Note that the entries use the older PyModuleDef_Slot structure, rather than PySlot.

If the array contains slots corresponding to PyModuleDef members, the values must match. For example, if you use Py_mod_name in !m_slots, PyModuleDef.m_name must be set to the same pointer (not just an equal string).

3.5

Prior to version 3.5, this member was always set to NULL, and was defined as:

Older structure defining additional slots of a module.

Note that a !PyModuleDef_Slot array may be included in a !PySlot array using Py_mod_slots, and vice versa using Py_slot_subslots.

Each !PyModuleDef_Slot structure modslot is interpreted as the following PySlot structure:

(PySlot){
   .sl_id=modslot.slot,
   .sl_flags=PySlot_INTPTR | sub_static,
   .sl_ptr=modslot.value
}

where sub_static is PySlot_STATIC if the slot requires the flag (such as for Py_mod_methods), or if this flag is present on the "parent" !Py_mod_slots slot (if any).

Corresponds to PySlot.sl_id.

Corresponds to PySlot.sl_ptr.

3.5

The type of PyModuleDef objects.

Slot ID <PySlot.sl_id> that works like Py_slot_subslots, except it specifies an array of PyModuleDef_Slot structures.

3.15

Create a new module object, given the definition in def. This is a macro that calls PyModule_Create2 with module_api_version set to PYTHON_API_VERSION, or to PYTHON_ABI_VERSION if using the limited API <limited-c-api>.

Create a new module object, given the definition in def, assuming the API version module_api_version. If that version does not match the version of the running interpreter, a RuntimeWarning is emitted.

Return NULL with an exception set on error.

This function does not support slots. The ~PyModuleDef.m_slots member of def must be NULL.

[!NOTE] Most uses of this function should be using PyModule_Create instead; only use this if you are sure you need it.

This macro calls PyModule_FromDefAndSpec2 with module_api_version set to PYTHON_API_VERSION, or to PYTHON_ABI_VERSION if using the limited API <limited-c-api>.

3.5

3.15

Prefer PyModule_FromSlotsAndSpec in new code.

Create a new module object, given the definition in def and the ModuleSpec spec, assuming the API version module_api_version. If that version does not match the version of the running interpreter, a RuntimeWarning is emitted.

Return NULL with an exception set on error.

Note that this does not process execution slots (Py_mod_exec). Both PyModule_FromDefAndSpec and PyModule_ExecDef must be called to fully initialize a module.

[!NOTE] Most uses of this function should be using PyModule_FromDefAndSpec instead; only use this if you are sure you need it.

3.5

3.15

Prefer PyModule_FromSlotsAndSpec in new code.

Process any execution slots (Py_mod_exec) given in def.

3.5

3.15

To run a module's own execution slots, prefer PyModule_Exec, which works on modules that were not created from a PyModuleDef structure.

Support functions

The following functions are provided to help initialize a module object. They are intended for a module's execution slot (Py_mod_exec), the initialization function for legacy single-phase initialization <single-phase-initialization>, or code that creates modules dynamically.

Add an object to module as name. This is a convenience function which can be used from the module's initialization function.

On success, return 0. On error, raise an exception and return -1.

Example usage:

static int
add_spam(PyObject *module, int value)
{
    PyObject *obj = PyLong_FromLong(value);
    if (obj == NULL) {
        return -1;
    }
    int res = PyModule_AddObjectRef(module, "spam", obj);
    Py_DECREF(obj);
    return res;
 }

To be convenient, the function accepts NULL value with an exception set. In this case, return -1 and just leave the raised exception unchanged.

The example can also be written without checking explicitly if obj is NULL:

static int
add_spam(PyObject *module, int value)
{
    PyObject *obj = PyLong_FromLong(value);
    int res = PyModule_AddObjectRef(module, "spam", obj);
    Py_XDECREF(obj);
    return res;
 }

Note that Py_XDECREF() should be used instead of Py_DECREF() in this case, since obj can be NULL.

The number of different name strings passed to this function should be kept small, usually by only using statically allocated strings as name. For names that aren't known at compile time, prefer calling PyUnicode_FromString and PyObject_SetAttr directly. For more details, see PyUnicode_InternFromString, which may be used internally to create a key object.

3.10

Similar to PyModule_AddObjectRef, but "steals <steal>" a reference to value (even on error). It can be called with a result of function that returns a new reference without bothering to check its result or even saving it to a variable.

Example usage:

if (PyModule_Add(module, "spam", PyBytes_FromString(value)) < 0) {
    goto error;
}

3.13

Similar to PyModule_AddObjectRef, but steals <steal> a reference to value on success (if it returns 0).

The new PyModule_Add or PyModule_AddObjectRef functions are recommended, since it is easy to introduce reference leaks by misusing the PyModule_AddObject function.

[!NOTE] Unlike other functions that steal references, PyModule_AddObject() only releases the reference to value on success.

This means that its return value must be checked, and calling code must Py_XDECREF value manually on error.

Example usage:

PyObject *obj = PyBytes_FromString(value);
if (PyModule_AddObject(module, "spam", obj) < 0) {
    // If 'obj' is not NULL and PyModule_AddObject() failed,
    // 'obj' strong reference must be deleted with Py_XDECREF().
    // If 'obj' is NULL, Py_XDECREF() does nothing.
    Py_XDECREF(obj);
    goto error;
}
// PyModule_AddObject() stole a reference to obj:
// Py_XDECREF(obj) is not needed here.

3.13

Add an integer constant to module as name. This convenience function can be used from the module's initialization function. Return -1 with an exception set on error, 0 on success.

This is a convenience function that calls PyLong_FromLong and PyModule_AddObjectRef; see their documentation for details.

Add a string constant to module as name. This convenience function can be used from the module's initialization function. The string value must be NULL-terminated. Return -1 with an exception set on error, 0 on success.

This is a convenience function that calls PyUnicode_InternFromString and PyModule_AddObjectRef; see their documentation for details.

Add an int constant to module. The name and the value are taken from macro. For example PyModule_AddIntMacro(module, AF_INET) adds the int constant AF_INET with the value of AF_INET to module. Return -1 with an exception set on error, 0 on success.

Add a string constant to module.

Add a type object to module. The type object is finalized by calling internally PyType_Ready. The name of the type object is taken from the last component of ~PyTypeObject.tp_name after dot. Return -1 with an exception set on error, 0 on success.

3.9

Add the functions from the NULL terminated functions array to module. Refer to the PyMethodDef documentation for details on individual entries (due to the lack of a shared module namespace, module level "functions" implemented in C typically receive the module as their first parameter, making them similar to instance methods on Python classes).

This function is called automatically when creating a module from PyModuleDef (such as when using multi-phase-initialization, PyModule_Create, or PyModule_FromDefAndSpec). Some module authors may prefer defining functions in multiple PyMethodDef arrays; in that case they should call this function directly.

The functions array must be statically allocated (or otherwise guaranteed to outlive the module object).

3.5

Set the docstring for module to docstring. This function is called automatically when creating a module from PyModuleDef (such as when using multi-phase-initialization, PyModule_Create, or PyModule_FromDefAndSpec).

Return 0 on success. Return -1 with an exception set on error.

3.5

Indicate that module does or does not support running without the global interpreter lock (GIL), using one of the values from Py_mod_gil. It must be called during module's initialization function when using single-phase-initialization. If this function is not called during module initialization, the import machinery assumes the module does not support running without the GIL. This function is only available in Python builds configured with --disable-gil. Return -1 with an exception set on error, 0 on success.

3.13

Module lookup (single-phase initialization)

The legacy single-phase initialization <single-phase-initialization> initialization scheme creates singleton modules that can be looked up in the context of the current interpreter. This allows the module object to be retrieved later with only a reference to the module definition.

These functions will not work on modules created using multi-phase initialization, since multiple such modules can be created from a single definition.

Returns the module object that was created from def for the current interpreter. This method requires that the module object has been attached to the interpreter state with PyState_AddModule beforehand. In case the corresponding module object is not found or has not been attached to the interpreter state yet, it returns NULL.

Attaches the module object passed to the function to the interpreter state. This allows the module object to be accessible via PyState_FindModule.

Only effective on modules created using single-phase initialization.

Python calls PyState_AddModule automatically after importing a module that uses single-phase initialization <single-phase-initialization>, so it is unnecessary (but harmless) to call it from module initialization code. An explicit call is needed only if the module's own init code subsequently calls PyState_FindModule. The function is mainly intended for implementing alternative import mechanisms (either by calling it directly, or by referring to its implementation for details of the required state updates).

If a module was attached previously using the same def, it is replaced by the new module.

The caller must have an attached thread state.

Return -1 with an exception set on error, 0 on success.

3.3

Removes the module object created from def from the interpreter state. Return -1 with an exception set on error, 0 on success.

The caller must have an attached thread state.

3.3