Python and COM

Python and COM

Greg Stein

Mark Hammond

Tutorial Agenda

• Introduction to COM

• PythonCOM Framework

• Using Python as a COM client

• Using Python as a COM server

• Advanced topics

• Futures

Introduction to COM

COM/OLE and ActiveX

• Component Object Model– Specification for implementing and defining

objects

• OLE is the old name, COM is the official name, ActiveX is the marketing name– All the same - the Microsoft Marketing

Machine

What is a COM interface?

• A technique for implementing objects– Uses a “vtable” to define methods– Does not have properties

• Basically a C++ object with only public methods– But not C++ specific - just borrowed

implementation technique– Allows implementation from other languages– All interfaces have a unique ID

IUnknown

• Base class of all interfaces– Every COM object must implement

• Defines object lifetimes– Reference counted using “AddRef” and

“Release” methods

• Defines techniques for querying the object for something useful– QueryInterface method

• No other functionality - simply defines these 3 methods

Custom interfaces

• Any interface derived from IUnknown– Therefore must follow IUnknown rules for

lifetimes

• Derived?– Means object can be used as its base. Simple

implementation using vtables

• All interfaces are custom interfaces– Not a standard part of COM per-se, just follow

its rules

Objects vs. Interfaces

• Interfaces simply define functionality

• Objects, once instantiated, implement the interface– Object class also has unique ID

• Objects always provide multiple interfaces– At least IUnknown and some other functional

interface

CLSIDs, GUIDs, UUIDs, IIDs

• COM defines 128 bit identifier, and API for creating them– “High degree of certainty” that these are globally

unique

• All use the same type and implementation, acronym reflects different usage– IID == Interface ID, GUID == Globally Unique

Identifier, CLSID == Class ID, UUID == Universally Unique Identifier, etc

– API for converting to and from Strings

Registering Objects

• Objects register themselves in the Windows Registry– Register with their Unique CLSID

• Also register a name for the object– COM provides API for translating, but names

are not guaranteed unique– Many objects self register

Creating Objects

• Standard COM API for creation– CoCreateInstance, passing:

• CLSID identifying the object to create

• IID identifying the initial interface requested

C++ Pseudo Code

// Create an object, but only get back

// IUnknown pointer, with new reference

IUnknown *pUnk = CoCreateInstance(“MyObject”, ...)

// Ask the object for a pointer to a useful implementation!

pUseful = pUnk->QueryInterface( IID_IUseful, ...)

pUnk->Release(); // finished with this.

pUseful->DoSomethingUseful();

…

pUseful->Release(); // Object now dies…

Custom Interface Example1 of 2

• Native Interfaces using Word– You would be unlikely to use Word this way– Demonstrative purposes only!

• >>> import ni, win32com, pythoncom>>> o=pythoncom.CoCreateInstance \ ("Word.Application", None, pythoncom.CLSCTX_ALL, pythoncom.IID_IUnknown)>>> o<PyIUnknown at 0x834b04 with obj at 0x423474>

Custom Interface Example2 of 2

• >>> o.QueryInterface( \ pythoncom.IID_IPersist)<PyIPersist at 0x85dd54 with obj at 0x423464>

• Almost identical to the pseudo code above– In fact, Python is far better than C++, as long as

we support the required interfaces natively

• No AddRef or Release required, or even exposed– Release() currently exposed, but not for long!

IDispatch - poor man’s COM1 of 2

• Also known as “Automation”

• Derived from IUnknown

• Defines vtable methods to determine “dispatch methods and properties” at runtime– Perfect for scripting languages which have no

compile step, or which are not C++!

• Optionally uses Type Libraries so optimizations can be made at compile time

IDispatch - poor man’s COM2 of 2

• What many people know as COM– Microsoft marketing machine– In reality, a small, but somewhat useful part of

COM

• Many useful COM interfaces do not support IDispatch– Native MAPI, Active Scripting/Debugging,

ActiveX Controls, Speech Recognition, etc

• Very hard from C/C++, very easy from VB

Core InterfacesIntroduction

• COM tends to use interfaces for everything. Example:– Instead of using a file pointer/handle, a

“Stream” interface is used, which provides file like semantics

– Anyone free to implement the stream interface using any technique they choose

– Such interfaces not necessarily part of COM per-se, but we consider them “core interfaces”

Core InterfacesEnumerators

• Enumerators provide access into a list of values

• Provides Next, Skip, Reset and Clone methods

• Different enumerator interfaces for different types:– IEnumGUID - Enumerate list of GUID’s– IEnumFooBar - Enumerate list of FooBars!

Core InterfacesCollections

• Alternative technique for accessing lists

• Usually only used via IDispatch– Uses “tricks” only IDispatch has available, such

as properties!– Therefore not a real interface

• Used to provide array like semantics for VB, etc– Methods include Count() and Item(). Count

often implied by len(), Item() often omitted.

Core InterfacesStreams and Storage

• IStream provides file like semantics

• IStorage provides file system like semantics

• Programs can write to this specification without needing to know the destination of the data

• COM provides implementations of these for “structured storage files”

Core InterfacesMonikers

• Provide file name to object mapping semantics

• Fundamental concept is to provide an indirection level to an underlying object, and a program neutral way of accessing the underlying object– File and URL Monikers do just that– Pointer monikers allow anyone to implement an

abstract indirection to an object (e.g., into a message store, etc)

Core InterfacesConnectionPoints

• Provides simple callback functionality

• Client sets up connection point object

• Object passed to Connection Point Container object

• Container calls methods on the Connection Point when appropriate

• Typically used as an event mechanism (e.g., ActiveX Controls). This is how VB finds the list of events for an object.

Core InterfacesAnd the Rest

• Plenty of others not listed here

• Anything in core PythonCOM is considered core– By us, anyway - YMMV :-)

• Check out the sources, Help Files, or forthcoming documentation– Who was going to write that?– Extensions to PythonCOM - present and future

Error Handling

• All methods use HRESULT return code– Multiple “success” codes, and many failure

codes– ISupportErrorInfo interface for richer error

information

• IDispatch uses EXCEP_INFO structure

• PythonCOM transparently maps these

• More detail in Server section

PythonCOM Framework

PythonCOM Framework

• Supports use of Python for both COM servers and COM clients

• Easy for the Python programmer

• Dispatch friendly with core support for most common vtable interfaces

• Easily extended for new vtable interfaces

PythonCOM Extensions

• Model allows for COM extension DLLs– Once loaded, looks like native support to the

Python programmer

• MAPI, ActiveX Scripting and Debugging all use this technique– Import them once, and PythonCOM will serve

up their interfaces

• Makes for stable core, with more frequent extension releases

Using Python as a COM client

Python COM ClientsThe Problem

• Calling a COM object from Python

• COM = vtable = C++ (not Python)

• IDispatch removes vtable requirement– Imposes coding burden on client– IDispatch is still vtable based, so core problem

remains

Python COM ClientsThe Answer

• We need an intermediary between a Python object and COM’s vtables– These are called “interfaces” (c.f. “gateways”

for the server side - poor choice of terminology, but this is what we use!)

PythonCOM Interfaces1 of 3

• Very similar to standard Python extension modules

• Conceptually identical to wrapping any C++ object in Python– 1:1 mapping between the COM pointer and

Python object– Pulls apart arguments using PyArg_ParseTuple– Makes call on underlying pointer– Handles errors, exceptions, and return values


Interface

Interface

Interface

v-ta

ble

inte

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e

C++Python

Client

Server

PythonCOM


InterfaceIDispatch

IDis

patc

h in

terf

ace

C++Python

Client ServerWrapper

PythonCOM

IDispatch vs. vtable

• IDispatch implemented in PythonCOM.dll like any other interface– No Dynamic logic implemented in DLL– Only GetIDsOfNames and Invoke exposed

• win32com.client Python code implements all IDispatch logic

• Calls the above 2 methods dynamically to obtain method and property information

IDispatch Implementation

• 2 modes of IDispatch usage– Dynamic, where no information about an object

is known at runtime• All determination of methods and properties made

at runtime

– Static, where full information about an object is known before hand

• Information comes from a “Type Library”

• Not all objects have Type Libraries (including Python objects!)

Dynamic IDispatch Implementation1 of 5

• Implemented by win32com.client.dynamic– Also makes use of win32com.client.build– Uses __getattr__ and __setattr__ methods in

Python to implement its magic


• Not perfect solution as– __getattr__ has no idea if the attribute being

requested is a property reference or a method reference

– No idea if the result of a method call is required (i.e., is it a sub or a function)

– Python must guess at the variable types– Big problem tends to be “byref” params - by

default these are not handled


• win32com.client.Dispatch kicks it all off

• Demo>>> import ni

>>> from win32com.client import Dispatch

>>> w=Dispatch(“Word.Application”)

>>> w.Visible = 1

• Starts Winword, and makes it visible

Dynamic Dispatch Implementation4 of 5

• Pros– No setup steps - just works– Provides quick scripting access to components

• Cons– Relatively slow– You need to know the object model of the

target. Not self documenting.• Actually, Python can make many objects self

documenting, but this is beyond the scope of this

Dynamic Dispatch Implementation5 of 5

• Smart Dispatch vs. Dumb Dispatch– To overcome some potential problems, Python

attempts to use Type Info even for dynamic objects

– Slows down considerably for certain objects– win32com.client.DumbDispatch provides

alternative implementation which does not attempt to locate type information

• For many servers, will provide excellent results and speed

Static Dispatch Implementation1 of 4

• Generates .py file from Type Information– win32com.client.makepy does this

• Python code then imports this module

• Python knows everything about the object– No confusion between methods and properties– Byref args handled correctly– No dynamic lookups - much faster


• DemoC:\> cd “\Program Files\Microsoft Office\Office”

C:\> \python\python \python\win32com\client\makepy.py msword8.olb > \python\msword8.py

...

C:> start python

>>> import msword8 # grind, grind :-)

>>> w = msword8.Application()

>>> w.Visible = 1


• Pros– ByRef args handled correctly

• Result becomes a tuple in that case

– All types handled correctly• Python knows the type required, so doesnt have to

guess. More scope to coerce

– Significantly faster– Python source file documents methods and

properties available


• Cons– Need to hunt down type library– Need to enter cryptic command to generate code– No standard place to put generated code– Compiling code may take ages

• Not real problem, as this is a once only step

– Type library may not be available

• Many Cons listed are not permanent - help would be appreciated!

Dispatch, VARIANTs and Python Types

• VARIANT– COM concept for IDispatch interface

• Just a C union, with a flag for the type, and an API for manipulating and converting

– IDispatch always uses VARIANT objects• In reality, COM is not typeless - most servers

assume a particular type in the variant

– Most (only!) complex code in PythonCOM deals with VARIANT conversions

Dispatch, VARIANTs and Python Types

• Python has 2 modes of conversion– Python type drives VARIANT type

• Python knows no better

• Creates VARIANT based on type of Python object

– Known type drives VARIANT type• For static IDispatch, Python often known exactly

type required

• Attempt to coerce the Python object to VARIANT of this type

win32com.client Files1 of 2

• makepy.py, dynamic.py– Static and dynamic IDispatch implementations

respectively

• build.py– Utility code used by both modules above

• CLSIDToClass.py– Manages dictionary of Python classes, mapped

by CLSID. Code generated by makepy.py automatically populates this.

win32com.client Files2 of 2

• combrowse.py– Basic COM browser that requires Pythonwin.

Simply double-click on it.

• tlbrowse.py– Basic Type Library browser that requires Pythonwin

• util.py– Utiility helpers

• connect.py– Connection point client base class

Client Side Error Handling1 of 2

• Client interfaces raise pythoncom.com_error exception

• Exception consists of:– HRESULT

• 32 bit error code, defined by OLE

– Error Message• Should be language independant

– (cont.)

Client Side Error Handling2 of 2

• COM Exception Tuple– Tuple of (wcode, AppName, AppMessage,

HelpFile, HelpContext, scode), all of which are application defined

– Exception object itself, or any part of it, may be None

• Arg Error– Integer containing the argument number that

caused the error– Often None if error does not relate to specific

argument

SWIG and COM Client Interfaces1 of 3

• Recent changes to SWIG allow it to generate client side native interfaces– ie, any custom interface not based on IDispatch

can be generated

• Uses existing SWIG functionality and M.O.– ie, maintain .i files, and SWIG generates .c files

• Native MAPI support generated this way– Pretty serious API, and it works a treat!


• Sample .i from MAPI#define TABLE_SORT_DESCEND TABLE_SORT_DESCEND

HRESULT MAPIInitialize( MAPIINIT_0 *INPUT);HRESULT MAPILogonEx(

ULONG INPUT, TCHAR *inNullString,...IMAPISession **OUTPUT

);


• Notes– #defines are carried into module– Many functions are completely trivial– SWIG handles input/output params– Scope for even better integration with COM

• e.g., maybe the first cut at the .i could be generated from the Type Info.

– More work and discussions with Dave Beazley needed!

Using Python as a COM server

Python COM ServersThe Problem

• Exposing a Python object as a COM object

• COM = vtable = C++ (not Python)

• IDispatch removes vtable requirement– Imposes coding burden on client– Some interfaces are defined as a vtable

• Answer: we need an intermediary between COM’s vtables and a Python object– These are called “gateways”

Gateways1 of 2

• Gateways act as the intermediary– Hold reference to the Python object– Map C++ method calls into Python calls– Map parameters and return values

• A gateway is a C++ object implementing a particular COM interface

• Gateways are registered with the framework and instantiated as needed to support particular interfaces as they are requested

Gateways2 of 2

• The default gateway supports IDispatch– All Python COM servers automatically support

IDispatch

• Default also supports ISupportErrorInfo, a standard interface for returning extended error information

Gateways3 of 3

Gateway

Gateway

Gateway

v-ta

ble

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C++ Python

Client

Wrapper Server

PythonCOM

Calling Python Methods

• The Python COM framework defines an IDispatch-oriented protocol for how the gateways call into Python:– _QueryInterface_ : determine support for a

particular COM interface– _GetIDsOfNames_ : look up a dispatch

identifier (DISPID) for a given name– _Invoke_ : invoke a method with specified

parameters

Policies1 of 2

• “Features” of the gateway protocol:– Non-intuitive for a Python programmer– Usually requires support structures for the

DISPID handling– Subtleties with some of the parameters and

return values

• Result: hard for Python programmers to write a COM server

• Answer: “policy objects”

Policies2 of 2

• A “policy” specifies how to implement a Python COM server

• The policy object maps the gateway protocol to the given implementation policy

• The default policy is usually sufficient

• Custom policies may be created and used– An advanced topic (discussed later)

Instantiation1 of 3

• The framework calls the CreateInstance function in the win32com.server.policy module– Hard-wired call to CreateInstance, but behavior

can easily be hooked through custom policies

• When your COM object is registered, an additional registry key specifies the creator function– Typically “mymodule.MyClass”

Instantiation2 of 3

• The registry key is read by the default policy and used to instantiate your object

• COM does not provide additional parameters to your creator function (the __init__ method)– Make sure that any parameters have defaults– COM+ will provide this capability

• Registry can specify a custom policy

Instantiation3 of 3

PythonCOM policy.py

CreateInstance(clsid, riid)

clsid, riid

returned

Interface

creates

pUnk

clsid, riid

returned

The Default Policy

• Python server objects (instances) are annotated with special attributes– Typically specified as class attributes– Most are optional

• _public_methods_– A list of strings specifying the methods that

clients are allowed to call– This is the only required attribute

A Quick Example

class MyPythonServer:

_public_methods_ = [ ‘SomeMethod’ ]

def SomeMethod(self, arg1, arg2):

do_some_work(arg1)

return whatever(arg2)

• Note that the only difference for the Python programmer is the addition of the _public_methods_ attribute

Useful Attributes

• _public_attrs_ : what Python attributes should be exposed as COM Properties

• _readonly_attrs_ : which of the above should be considered read-only

• _com_interfaces_ : what COM interfaces beyond IDispatch are supported

Wrapping1 of 3

• The process of associating a gateway instance and a policy instance with a particular Python instance is known as “wrapping”

• Similarly, retrieving the Python instance is known as “unwrapping”

• Objects returned by Python COM servers must be wrapped (the framework does not automatically wrap)

Wrapping2 of 3

Gateway

Policy

Server

This diagram shows the organization of theobjects involved in a Python COM server andwhere the “wrapping” term came from

Wrapping3 of 3

• Wrapping an object that will be returned:

from win32com.server import util...def method(self, arg):

ob = whatever(arg)return util.wrap(ob)

• Unwrapping (of an argument) is rare– You must know the object is a Python object

(and what to do with it once unwrapped)– Usually used in relatively closed systems

Error Handling1 of 3

• COM defines simple result codes with the HRESULT type and associated constants

• Extended error information includes description, help file, context, etc

• Returned via EXCEP_INFO structure in IDispatch or through ISupportErrorInfo

• Framework maps Python exceptions to COM result codes and exceptions


• If the Python exception is an instance, then framework looks for special attributes to fill in COM extended exception information– Just raise an instance with the right attributes– See exception.Exception utility class

• Otherwise, the framework does its best


• When called via IDispatch, it returns the exception via EXCEP_INFO

• For non-Dispatch calls, the caller may follow up by using ISupportErrorInfo to retrieve the exception

• ISupportErrorInfo is part of the base gateway class and is always present

Collections1 of 3

• Collections are sequence-like objects that typically implement the Add, Remove, and Item methods and a Count property

• Some Collections (such as those provided natively by VB) can be indexed using numbers (acts as a sequence) or using strings (acts as a mapping)

• win32com.server.util.Collection is a simple numerically indexed Collection class

Collections2 of 3

• The Item method is special– It should be the “default” method, meaning that

VB can implicitly call it without using its name– The predefined DISPID_VALUE value refers to

the default method– Item can be called with one parameter (the

index) or with two parameters (an index and a new value to place at that index)

– This duality is not handled well by the default policy nor server.util.Collection

– Also beware the numeric vs. string indexing

Collections3 of 3

• The Python COM framework defines returning a list or tuple to mean returning a SAFEARRAY of VARIANT values– This means your object must explicitly return an

object that obeys the Collection protocol– A custom policy could be used to automatically

wrap sequences with a Collection– Only recognizes list and tuple

• avoids treating a string as a sequence

• instances are not checked for sequence behavior

Enumerators1 of 3

• Enumerators are used by clients to enumerate a collection (sequence)– VBScript automatically fetches an enumerator

for script code such as:for each item in collection

• Standard COM protocol uses the predefined DISPID_NEWENUM value and calls IDispatch::Invoke()– Default policy calls your _NewEnum method

Enumerators2 of 3

• IEnumVARIANT is the interface used by Automation clients (such as VB)– Your returned enumerator must implement the

IEnumVARIANT interface– Values returned from Next() are VARIANTs

(see client section for discussion of COM enumerator interfaces)

– Support for IEnumVARIANT part of core– Python datatypes are easily coerced into

VARIANTs by the IEnumVARIANT gateway

Enumerators3 of 3

• win32com.server.util.NewEnum(seq) will return an enumerator for a given sequence

• Custom enumerators are easily written:– Dynamic sequences– Special handling of enumerated values– Subclass from server.util.ListEnumerator,

ListEnumeratorGateway, or write from scratch

• New gateways needed for interfaces other than IEnumVARIANT

Server Utilities

• Various functionality available in win32com.server.*– ...connect : connection points– ...exception : exception handling– ...policy : framework support– ...register : server object registration– ...util : miscellaneous utilities

win32com.server.connect

• Supplies utilities and classes for the server side of connection points

win32com.server.exception

• Exports a single class: Exception

• Constructor has keyword arguments for the status code, description, help file, etc.

• The Exception class places these values into instance variables

• The Python COM framework picks up the values for returning to the caller

win32com.server.policy

• Framework knows about this file– Hard-coded reference, so it must exist

• Provides CreateInstance for the framework– Provides hooks for custom policies and

dispatchers

• Defines various standard policies and dispatchers– Future: the policies and dispatchers will move

out to separate files for easier maintainability

win32com.server.register

• Utilities for registering your COM servers

• Two primary functions:– RegisterServer()– UnregisterServer()

• Typically, registration for servers in a file is performed when the file is run from the command line (e.g. “python myservers.py”)

• RegisterServer() has many options; see its doc string for more information

win32com.server.register Exampleclass MyClass:

_public_methods_ = [ “MyMethod” ]

# … class definition

if __name__ == “__main__”:

import sys

from win32com.server import register

if len(sys.argv) > 1 and sys.argv[1] == “--unregister”:

register.UnregisterServer(“{…}”, “The.ProgID”)

else:

register.RegisterServer(“{…}”, “MyModule.MyClass”,

progID=“The.ProgID”)

win32com.server.util

• wrap()

• unwrap()

• NewEnum()– ListEnumerator class– ListEnumeratorGateway class

• Collection class

win32com.makegw

• Tool for interfaces and gateways– SWIG now my preference for interfaces - gateways

somewhat harder

• Generate once, and never again– compare with SWIG, which allows multiple

generations - particularly useful as support is added after initial generation

• Better than hand-coding– Active Scripting, Debugging and some others done

this way

Advanced Topics

Advanced: Dispatchers1 of 2

• Debugging and tracing utility– Almost identical to policies; simply delegate to

actual policy

• Only used during development, so zero runtime overhead in release

• Implementation is not for speed, but for assistance in debugging– e.g., IIDs translated if possible to names, often

using the registry or dictionary lookups, etc

Advanced: Dispatchers2 of 2

• Log information about your server– All method calls made– All IDispatch mapping– All QueryInterface requests

• Dispatchers available that send to various debugging “terminals”– win32dbg debugger, win32trace utility, existing

stdout, etc.– Easy to write your own if you have specific

debugging requirements

Advanced: Wrapping1 of 5

• All Python server objects are wrapped with at least two objects: the policy and the gateway– Caveat: a custom policy may implement the

actual server rather than using another object (see win32com.servers.dictionary)

– Dispatchers can actually add a third layer into this group


• Since a gateway is referenced with a C++ interface pointer, Python cannot hold the reference– Wrap once more with a framework “interface”

(we’ll call it a PyInterface to distinguish from COM interfaces)

– The PyInterface is removed by the framework (exposing the C++ pointer) when a PyInterface is returned by a server


Gateway

Policy

Server

Interface

Pyt

hon

C+

+

Returned to COM client(the framework removes the PyInterface)


• win32com.pythoncom.WrapObject() wraps a Python object with a gateway and a PyInterface– Pass it the policy object (which is wrapping the

Python server object)– Optional parameter specifies the IID of a

gateway to use for the wrapping (the gateway must be registered with the COM framework)


• Unwrapping is performed through a special COM interface: IUnwrapPythonObject

• pythoncom.UnwrapObject() queries for this interface on the COM object held within the PyInterface object that is passed

• The base gateway class implements this COM interface (so all gateways have it)

• The interface’s single method returns the gateway’s underlying Python object

Advanced: Custom Policies1 of 7

• Why use a custom policy?– Special error handling, creation, calling

mechanisms, validation, etc– Write the policy class and enter the appropriate

information into the registry so that the framework will use your policy

– Be sure to use your custom policy when wrapping your objects


• Other provided policies– BasicWrapPolicy : handy base class– MappedWrapPolicy : low level mapping-based

handling of names and properties and methods– DesignatedWrapPolicy : build onto the Mapped

policy a way for objects to easily specify the properties and methods

– DynamicPolicy : determine methods and properties dynamically


• Example: custom instantiation– A single Python COM server was used to

represent multiple COM objects– At instantiation time, it used the CLSID passed

to the policy to look in the registry for more detailed information

– A child/sub object was created, based on the registered information; the COM server provided some generic behavior for all of the child objects


• Example: error handling– Returning “KeyError” or other Python

exceptions to callers was undesirable– Wrap all Invokes with an exception handler that

would map Python errors into a generic error– Let through pythoncom.com_error unchanged– If a “magic” registry value was present, then a

full traceback was placed into the exception (rather than simply “internal error”)


• Example: data validation– If the server object had a _validation_map_

attribute, then a custom validation method would be called for all Property “puts”

– _validation_map_ would map a Property name to a type signature that the _validate_() method would test against

– The Invoke method was hooked to call the _validate_() method


• Example: functions for Property get/put– The Item() method in Collections is really

treated as a parameterized property– Using a custom policy, get_Item() can be

differentiated from put_Item()– Allowed for get_Count() and the absence of

put_Count() implied read-only


• Example: alter mechanism for specifying the available properties– Using the _validation_map_ from a previous

example, the available properties are easily derived (simply the keys of the mapping)

– Avoided duplication of property specification (one in _validation_map_ and one in _public_attrs_)

Advanced: Threading1 of 2

• Python is normally “single threaded”; the least capable COM threading model

• With care, it could be possible to mark an object as “free threaded” to fool how COM handles the object, but Python will continue to allow only one thread per process to run

• This behavior is fine for many applications where Python is a COM client, but it breaks down for some server scenarios

Advanced: Threading2 of 2

• The problem can be reduced by applying patches with allow Python to be truly free-threaded– Slows down single thread case– Applies mainly to multiprocessor use

• More work on threading is needed and is in progress on the Thread-SIG

Futures

Future Directions

• Auto wrap and unwrap

• COM+

• SWIG

• makepy

Future: Auto Wrapping

• This could be done today, but wasn’t:– Leaving it to Python increased flexibility– Complexity involved with needing a way to

specify two things during any wrapping process: the policy and the gateway

• Moving to COM+ will be an opportune time to change

• Annotation through attributes will control wrapping process

Future: COM+1 of 3

• What is COM+ ?– Upcoming revision of COM– Runtime services: memory management,

interceptors, object model changes, language independence, etc

– see: http://www.microsoft.com/cominfo

Future: COM+2 of 3

• Python already has most of COM+’s facilities and matches its model strongly

• Huge win for Python:– Simplify COM programming even more– Will reduce the framework and associated

overheads– Better language compatibilities– Major reduction in dependence on vtables– Better type handling

Future: COM+3 of 3

• Any Python object can be a COM+ server, provided it is registered appropriately– Note that COM+ registration will be easier

• Auto wrapping

• “import somedll” will load the “metadata” from the DLL and automatically make its classes and constants available

Future: SWIG

• Depends largely on what Dave Beazley is willing to support!

• Interface support needs more work– Framework is OK– Mainly adding all interfaces and types to SWIG

library

• Gateways still a long way off– Future here quite uncertain

• Some sort of IDL parsing highly desirable

Future: makepy

• Functionally quite complete– Some cleanup desirable, but works well

• Architectural issues outstanding– Where does generated code go?

• Utilities for automatic generation– From program ID– Integration with COM browser– Integration with some GUI interface

Python and COM

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