PRELIMINARY
CONCEPT
        python

DESCRIPTION
        Python can be used to extend the LDMud driver. At the startup
        of LDMud a python script will be called that can register
        additional efuns. The python script can either be given
        on the command line using the --python-script option,
        or at compile time with the --with-python-script configuration
        option.

        The python script can import the builtin ldmud module.
        This module provides the following functions:

          - register_efun(name, function) -> None
                Registers a new efun name. This is not allowed during
                compilation of an LPC object.

                If the Python function has type annotations for its
                arguments and return value, the type is checked
                at compile and runtime. Union types can be specified
                as tuples of types.

          - unregister_efun(name) -> None
                Removes a python efun from registration. This is not
                allowed during compilation of an LPC object. The
                removal will only affect newly compiled code,
                already compiled code will produce errors when
                calling this efun.

          - register_socket(fd, function [,eventmask]) -> None
                Registers a socket <fd> to watch for events (like
                poll/select). The socket must be either given as
                an integer or an object with a fileno() method
                returning an integer. The function must be a callable
                accepting one argument, the actual event mask.
                <eventmask> may be an combination of select.POLLIN,
                select.POLLOUT and select.POLLPRI or a callable
                returning such a combination.

          - unregister_socket(fd) -> None
                Removes a previously registered socket from the
                watch list.

          - register_hook(hook, function) -> None
                Register a hook. The python function will be called
                whenever <hook> happens. <hook> can be one of the
                following:

                  ON_HEARTBEAT
                    Called without arguments for every backend loop

                  ON_OBJECT_CREATED
                    Called whenever an object was created, with the
                    object as its first and only argument. This call
                    happens before any LPC code of the object ran.

                  ON_OBJECT_DESTRUCTED
                    Called just before an object will be destructed,
                    with the object as its first and only argument.

                  ON_CHILD_PROCESS_TERMINATED
                    Called without any arguments whenever a SIGCHLD signal
                    was received. This could also happen for processes
                    spawned by the driver itself (eg. erq).

          - unregister_hook(hook, function) -> None
                Removes a hook function.

          - get_master() - > Object
                Returns the current master object.
                Returns None, if there is no master object (yet).

          - get_simul_efun() - > Object
                Returns the current simul-efun object
                (or None if there is none).


        This module provides the following types:

          - Object(filename)
                Corresponds to the LPC object type.
                On instantiation a filename for an object
                to search or load is required.

                Has the following members:

                  name
                      The object name

                  functions
                      Contains all the visible functions (private functions
                      are excluded) as attributes. They support the call
                      operator and contain the following attributes:

                      name
                          The name of the function

                      file_name
                          The file that contains the function's definition

                      line_number
                          The starting line number of the function's definition

                      arguments
                          A list of all arguments with their type, flags
                          (combination of LA_* constants) and position.

                      return_type
                          The return type as Python object (maybe missing if
                          unknown or mixed).

                      flags
                          A combination of the following flags:
                          LF_STATIC, LF_NOMASK, LF_VARARGS, LF_VIRTUAL and
                          LF_DEPRECATED

                      visibility:
                          One of the following:
                          VIS_PRIVATE, VIS_PROTECTED, VIS_VISIBLE, VIS_PUBLIC

                  variables
                      Contains all variables as attributes. They contain the
                      following attributes:

                      name
                          The name of the variable

                      value
                          The value of the variable. This attribute is writable
                          to assign a new value.

                      type
                          The type as a Python object (maybe missing if
                          unknown or mixed).

                      flags
                          A combination of the following flags:
                          VF_NOSAVE, VF_NOMASK, VF_VIRTUAL and VF_DEPRECATED

                      visibility:
                          One of the following:
                          VIS_PRIVATE, VIS_PROTECTED, VIS_VISIBLE, VIS_PUBLIC

          - LWObject(filename)
                Corresponds to the LPC lwobject type.
                On instantiation a filename of a blueprint to create
                a lightweight object from is required.

                Has the following members:

                  program_name
                      The program name (file name it was created from)

                  functions
                      Contains all the visible functions (private functions
                      are excluded) as attributes. They are similar to the
                      same member of the Object type.

                  variables
                      Contains all variables as attributes. They are similar
                      to the same member of the Object type.

          - Array([values | size])
                Corresponds to an LPC array.
                Can either be initialized with a list of values
                or to a given size.

                Supports element access with [], len() and __contains__.

          - Mapping([values | width])
                Corresponds to an LPC mapping.
                Can either be initialized with a dict, a list of tuples
                or as an empty mapping with a given width.

                Supports element access with [], len(), __contains__
                and has a width member.

          - Struct(object, name [, values])
                Corresponds to an LPC struct.
                On initialization the name of the struct definition and
                the correspopnding object is required. It can be initialized
                with a list of values or dict.

                Has the following members:

                  name
                      The name of the struct

                  program_name
                      The name of the program that defined the struct.

                  members
                      Contains all members as attributes. They contain the
                      following attributes:

                      name
                          The name of the member

                      value
                          The value of the member. This attribute is writable
                          to assign a new value.

                      type
                          The type as a Python object (maybe missing if
                          unknown or mixed).

          - Closure(object [,name [, lfun_object]])
               Corresponds to an LPC closure.
               On initialization a closure bound to <object> will be created,
               like a call to symbol_function(<name> [, <lfun_object>]).

               Supports function calls.

          - Symbol(name [, quotes])
              Corresponds to an LPC symbol.
              On initialization the name of the symbol is required.
              Optionally the number of quotes (at least 1) can be specified.

              Has two members: name and quotes.

          - QuotedArray(array [, quotes])
              Corresponds to an LPC quoted array.
              On initialization an array is required.
              Optionally the number of quotes (at least 1) can be specified.

              Has two members: array and quotes.

          - Lvalue(value)
              Creates an lvalue reference for the given value.

              Has two member: value and members.

              If the value is an array, mapping or string, then lvalues
              to its elements can be created with [].

              If the value is a struct, then lvalues to its members can
              be created with the members attribute. It contains all
              the struct members as attributes and will return an Lvalue
              object to the struct member.

        This module contains the following sub-namespaces:

          - efuns
              This namespace contains all original efuns (without any
              registered python efuns or simul-efuns). These can be called
              as a regular function.


        There is mapping of LPC values to Python values for the following types:
            int    <-> int(, bool)
            float  <-> float
            string <-> str
            bytes  <-> bytes

        Type definitions are translated in a similar fashion, additionally the
        following mappings are done:
            void   <-> None
            union  <-> tuple of types

EXAMPLE
        import ldmud

        def hello_world(name: str) -> int:
            print("Hello, world, %s!\n" % (name,))
            return 1

        ldmud.register_efun("hello", hello_world)

NOTES
        Just like simul-efuns python efuns can shadow real efuns. The
        original efun is then inaccessible for LPC code (except for code
        that was compiled before the efun was registered). Python efuns are
        nearly indistinguishable from real efuns, they also use the efun::
        prefix. However they can be detected with
            CLOSURE_IS_PYTHON_EFUN(get_type_info(#'efun,1))

        Without the prefix the order of name resolution for function calls is:
         1. lfuns
         2. simul-efuns
         3. python efuns
         4. real efuns

        Also just like simul-efuns python-registered efuns are called
        from LPC code that was compiled after the registration. LPC code
        that was compiled before the registration will still call the
        original efuns (or throw a compile error if that efun doesn't exist).
        Therefore such efuns should be registered in the python startup
        script.

        When a python efun is unregistered, code that was compiled while the
        registration was in effect will throw a runtime error. (Regardless
        of whether a driver efun with the same name exists or not.)

        There is a limit of 2048 python efuns. Not only registered, but also
        formerly registered - but now unregistered - efuns count toward that
        limit. Re-registering the same efun name again won't count a second
        time. (LPC code that was compiled during the previous registration
        will also call the new efun after the re-registration.)

        As LDMud is single-threaded, the python code will run in the same
        thread as the LPC machine. So any long-running python function will
        halt the MUD for all players. Hence python functions should return
        promptly and source out any lengthy tasks to another process. If
        other threads are spawned from python, then these threads are not
        allowed to access any LDMud functions or objects.

        Finally a note of caution: Don't change the meaning of base efuns
        fundamentally as it furthers confusion and hinders exchange of LPC
        code and knowledge between mudlibs.

HISTORY
        LDMud 3.5 implemented the python functionality.
        LDMud 3.6 added type checks.

SEE ALSO
        simul_efun(C)