The `comtypes.client` package 

The comtypes.client package implements the high-level comtypes functionality.

Creating and accessing COM objects 

comtypes.client exposes three functions that allow to create or access COM objects.

CreateObject(progid, clsctx=None, machine=None, interface=None, dynamic=False, pServerInfo=None)

Create a COM object and return an interface pointer to it.

progid specifies which object to create. It can be a string like "InternetExplorer.Application" or "{2F7860A2-1473-4D75-827D-6C4E27600CAC}", a comtypes.GUID instance, or any object with a _clsid_ attribute that must be a comtypes.GUID instance or a GUID string.

clsctx specifies how to create the object, any combination of the comtypes.CLSCTX_... constants can be used. If nothing is passed, comtypes.CLSCTX_SERVER is used.

machine allows to specify that the object should be created on a different machine, it must be a string specifying the computer name or IP address. DCOM must be enabled for this to work.

interface specifies the interface class that should be returned, if not specified comtypes will determine a useful interface itself and return a pointer to that.

dynamic specifies that the generated interface should use dynamic dispatch. This is only available for automation interfaces and does not generate typelib wrapper.

pServerInfo that allows you to specify more information about the remote machine than the machine parameter. It is a pointer to a COSERVERINFO. machine and pServerInfo may not be simultaneously supplied. DCOM must be enabled for this to work.

CoGetObject(displayname, interface=None)

Create a named COM object and returns an interface pointer to it. For the interpretation of displayname consult the Microsoft documentation for the Windows CoGetObject function. "winmgmts:", for example, is the displayname for WMI monikers:

wmi = CoGetObject("winmgmts:")

interface and dynamic have the same meaning as in the CreateObject function.

GetActiveObject(progid, interface=None)

Returns a pointer to an already running object. progid specifies the active object from the OLE registration database.

The GetActiveObject function succeeds when the COM object is already running, and has registered itself in the COM running object table. Not all COM objects do this. The arguments are as described under CreateObject.

All the three functions mentioned above will create the typelib wrapper automatically if the object provides type information. If the type library is not exposed by the object itself, the wrapper can be created by calling the GetModule function.

Using COM objects 

The COM interface pointer that is returned by one of the creation functions (CreateObject, CoGetObject, or GetActiveObject) exposes methods and properties of the interface (unless dynamic is passed to the function).

Since comtypes uses early binding to COM interfaces (when type information is exposed by the COM object), the interface methods and properties are available for introspection. The Python builtin help function can be used to get an overview of them.

Scripting.FileSystemObject is the progid of the Microsoft Scripting Runtime’s FileSystemObject; this COM object provides access to the computer’s file system, allowing scripts to create, read, update, and delete files and folders.

>>> from comtypes.client import CreateObject
>>> fso = CreateObject("Scripting.FileSystemObject")
>>> help(fso)  
Help on POINTER(IFileSystem...

Calling methods 

Calling COM methods is straightforward just like with other Python objects. They can be called with positional and named arguments.

Arguments marked [out] or [out, retval] in the IDL are returned from a sucessful method call, in a tuple if there is more than one. If no [out] or [out, retval] arguments are present, the HRESULT returned by the method call is returned. When [out] or [out, retval] arguments are returned from a sucessful call, the HRESULT value is lost.

If the COM method call fails, a COMError exception is raised, containing the HRESULT value.

Accessing properties 

COM properties present some challenges. Properties can be read-write, read-only, or write-only. They may have zero, one, or more arguments; arguments may even be optional.

The Scripting.Dictionary object provides a dictionary-like interface. This example demonstrates accessing and modifying the CompareMode property, which controls how keys are compared:

>>> dic = CreateObject("Scripting.Dictionary")
>>> dic.CompareMode  # default is 0, BinaryCompare
0
>>> dic.CompareMode = 1  # TextCompare
>>> dic.CompareMode
1

Properties with arguments (named properties)

Properties with arguments can be accessed using index notation. The following example starts Excel, creates a new workbook, and accesses the contents of some cells in the xlRangeValueDefault format (this code has been tested with version 2402 build 16.0.17328.20670):

>>> xl = CreateObject('Excel.Application')
>>> xl.Workbooks.Add()  
<POINTER(_Workbook) ptr=... at ...>
>>> from comtypes.gen.Excel import xlRangeValueDefault
>>> xl.Range["A1", "C1"].Value[xlRangeValueDefault] = (10,'20',31.4)
>>> xl.Range["A1", "C1"].Value[xlRangeValueDefault]
((10.0, 20.0, 31.4),)

Properties with optional arguments 

If you look into the Excel type library (or the generated comtypes.gen wrapper module) you will find that the parameter for the .Value property is optional, so it would be possible to get or set this property without the need to pass (or even know) the xlRangeValueDefault argument.

Unfortunately, Python does not allow indexing without arguments:

>>> xl.Range["A1", "C1"].Value[] = (10,"20",31.4)
Traceback (most recent call last):
  ...
    xl.Range["A1", "C1"].Value[] = (10,"20",31.4)
                               ^
SyntaxError: invalid syntax
>>> print(xl.Range["A1", "C1"].Value[])
Traceback (most recent call last):
  ...
    print(xl.Range["A1", "C1"].Value[])
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
SyntaxError: invalid syntax. Perhaps you forgot a comma?

So, comtypes must provide some ways to access these properties. To get a named property without passing any argument, you can call the property:

>>> print(xl.Range["A1", "C1"].Value())
((10.0, 20.0, 31.4),)

It is also possible to index with an empty slice or empty tuple:

>>> print(xl.Range["A1", "C1"].Value[:])
((10.0, 20.0, 31.4),)
>>> print(xl.Range["A1", "C1"].Value[()])
((10.0, 20.0, 31.4),)

To set a named property without passing any argument, you can also use the empty slice or tuple index trick:

>>> xl.Range["A1", "C1"].Value[:] = (3, 2, 1)
>>> print(xl.Range["A1", "C1"].Value[:])
((3.0, 2.0, 1.0),)
>>> xl.Range["A1", "C1"].Value[()] = (1, 2, 3)
>>> print(xl.Range["A1", "C1"].Value[()])
((1.0, 2.0, 3.0),)

The lcid parameter 

Some COM methods or properties have an optional lcid parameter. This parameter is used to specify a langauge identifier. The generated modules always pass 0 (zero) for this parameter. If this is not what you want you have to edit the generated code.

Converting data types 

comtypes usually converts arguments and results between COM and Python in just the way one would expect.

VARIANT parameters sometimes requires special care. A VARIANT can hold a lot of different types - simple ones like integers, floats, or strings, also more complicated ones like single dimensional or even multidimensional arrays. The value a VARIANT contains is specified by a typecode that comtypes automatically assigns.

When you pass simple sequences (lists or tuples) as VARIANT parameters, the COM server will receive a VARIANT containing a SAFEARRAY of VARIANTs with the typecode VT_ARRAY | VT_VARIANT.

Some COM server methods, however, do not accept such arrays, they require for example an array of short integers with the typecode VT_ARRAY | VT_I2, an array of integers with typecode VT_ARRAY | VT_INT, or an array a strings with typecode VT_ARRAY | VT_BSTR.

To create these variants you must pass an instance of the Python array.array with the correct Python typecode to the COM method.

Note

NumPy arrays are also an option, as described in the NumPy interop document.

The mapping of the array.array typecode to the VARIANT typecode is defined in the comtypes.automation module by a dictionary:

_arraycode_to_vartype = {
    "b": VT_I1,
    "h": VT_I2,
    "i": VT_INT,
    "l": VT_I4,

    "B": VT_UI1,
    "H": VT_UI2,
    "I": VT_UINT,
    "L": VT_UI4,

    "f": VT_R4,
    "d": VT_R8,
}

AutoCAD, for example, is one of the COM servers that requires VARIANTs with the typecodes VT_ARRAY | VT_I2 or VT_ARRAY | VT_R8 for parameters. This code snippet was contributed by a user:

"""Sample to demonstrate how to use comtypes to automate AutoCAD:
adding a point and a line to the drawing; and attaching xdata of
different types to them. The objective is to actually show how to
create variants of different types using comtypes.  Such variants are
required by many methods in AutoCAD COM API. AutoCAD needs to be
running to test the following code."""

import array
import comtypes.client

#Get running instance of the AutoCAD application
app = comtypes.client.GetActiveObject("AutoCAD.Application")

#Get the ModelSpace object
ms = app.ActiveDocument.ModelSpace

#Add a POINT in ModelSpace
pt = array.array('d', [0,0,0])
point = ms.AddPoint(pt)

#Add a LINE in ModelSpace
pt1 = array.array('d', [1.0,1.0,0])
pt2 = array.array('d', [2.0,2.0,0])
line = ms.AddLine(pt1, pt2)

#Add an integer type xdata to the point.
point.SetXData(array.array("h", [1001, 1070]), ['Test_Application1', 600])

#Add a double type xdata to the line.
line.SetXData(array.array("h", [1001, 1040]), ['Test_Application2', 132.65])

#Add a string type xdata to the line.
line.SetXData(array.array("h", [1001, 1000]), ['Test_Application3', 'TestData'])

#Add a list type (a point coordinate in this case) xdata to the line.
line.SetXData(array.array("h", [1001, 1010]),
              ['Test_Application4', array.array('d', [2.0,0,0])])

print "Done."

COM events 

Some COM objects support events, which allows them to notify the user of the object when something happens. The standard COM mechanism is based on so-called connection points.

Note

For the rules that you should observe when implementing event handlers you should read the COM servers with comtypes document.

GetEvents(source, sink, interface=None)

This functions connects an event sink to the COM object source.

Events will call methods on the sink object; the methods must be named interfacename_methodname or methodname. The methods will be called with a this parameter, plus any parameters that the event has.

interface is the outgoing interface of the source object; it must be supplied when comtypes cannot determine the outgoing interface of source.

GetEvents returns the advise connection; you should keep the connection alive as long as you want to receive events. To break the advise connection simply delete it.

ShowEvents(source, interface=None)

This function contructs an event sink and connects it to the source object for debugging. The event sink will first print out all event names that are found in the outgoing interface, and will later print out the events with their arguments as they occur. ShowEvents returns a connection object which must be kept alive as long as you want to receive events. When the object is deleted the connection to the source object is closed.

To actually receive events you may have to call the PumpEvents function so that COM works correctly.

PumpEvents(timeout)

This functions runs for a certain time in a way that is required for COM to work correctly. In a single-theaded apartment it runs a windows message loop, in a multithreaded apparment it simply waits. The timeout argument may be a floating point number to indicate a time of less than a second.

Pressing Control-C raises a KeyboardError exception and terminates the function immediately.

Examples 

Here is an example which demonstrates how to find and receive events from stdole.StdFont:

>>> font = CreateObject("StdFont")
>>> font  
<POINTER(Font) ptr=... at ...>

The ShowEvents function is a useful helper to get started with the events of an object in the interactive Python interpreter.

We call ShowEvents to connect to the events that StdFont fires. ShowEvents first lists the events that are present on the StdFont object:

>>> from comtypes.client import ShowEvents
>>> connection = ShowEvents(font)
# event found: FontEvents_FontChanged
>>> connection  
<comtypes.client._events._AdviseConnection object at ...>

We have assigned the return value of the ShowEvents call to the variable connection, this variable keeps the connection to StdFont alive and it will print events as they actually occur.

>>> font.Name = 'Arial'
Event FontEvents_FontChanged(None, 'Name')
>>> font.Italic = True
Event FontEvents_FontChanged(None, 'Italic')

The first parameter is always the this pointer passed as None for comtypes-internal reasons, other parameters depend on the event.

The PumpEvents() function will run a message loop for a certain time. comtypes prints the events as they are fired with their parameters:

>>> from comtypes.client import PumpEvents
>>> PumpEvents(0.01)  # The output will be in the form of "FontEvents_FontChanged(None, 'Name')".

To terminate the connection, we call the disconnect method. It may also be necessary to delete the connection variable and invoke the Python garbage collector. Afterward, no events from StdFont will be received anymore.

>>> connection.disconnect()
>>> del connection
>>> import gc
>>> _ = gc.collect()
>>> font.Name = 'Sans'  # Expected nothing

If we want to process the events in our own code, we use the GetEvents() function in a very similar way. This function must be called with the COM object as the first argument, the second parameter is a Python object, the event sink, that will process the events. The event sink should have methods named like the events we want to process. It is only required to implement methods for those events that we want to process, other events are ignored.

The following code defines a class that processes the FontEvents_FontChanged event, creates an instance of this class and passes it as second parameter to the GetEvents() function:

>>> from comtypes.client import GetEvents
>>> class EventSink(object):
...     def FontEvents_FontChanged(self, this, PropertyName):
...         print("FontChanged", PropertyName)
...         # add your code here
...
>>> sink = EventSink()
>>> connection = GetEvents(font, sink)
>>> font.Name = 'Arial'
FontChanged Name

Note

Event handler methods support the same calling convention as COM method implementations in comtypes. So the remarks about the “Implementing COM methods” section in the server document should be observed.

Typelibraries 

Accessing type libraries 

comtypes uses early binding even to custom COM interfaces. A Python class, derived from the comtypes.IUnknown class must be written. This class describes the interface methods and properties in a way that is somewhat similar to IDL notation.

It should be possible to write the interface classes manually, fortunately comtypes includes a code generator that does create modules containing the Python interface class (and more) automatically from COM typelibraries.

GetModule(tlib)

This function generates Python wrappers for a COM typelibrary. When a COM object exposes its own typeinfo, this function is called automatically when the object is created.

tlib can be the following:

an ITypeLib COM pointer from a loaded typelibrary
the pathname of a file containing a type library (.tlb, .exe or .dll)
a tuple or list containing the typelibrary’s GUID, optionally along with a major and a minor version numbers if versioning is required, plus optionally a LCID.
any object that has a _reg_libid_ and _reg_version_ attributes specifying a type library.

GetModule(tlib) generates two Python modules (if not already present): a first wrapper module and a second friendly module, within the comtypes.gen package with a single call and returns the second friendly module. If modules are already present, it imports the two modules and returns the friendly module.

A first wrapper module is created from the typelibrary, is containing interface classes, coclasses, constants, and structures. The module name is derived from the typelibrary guid, version numbers and lcid. The module name is a valid Python module name, so it can be imported with an import statement.

A second friendly module is also created in the comtypes.gen package with a shorter name that is derived from the type library name itself. It does import the wrapper module with an abstracted alias __wrapper_module__, also imports interface classes, coclasses, constants, and structures from the wrapper module, and defines enumerations from typeinfo of the typelibrary using enum.IntFlag. The friendly module can be imported easier than the wrapper module because the module name is easier to type and read.

For example, the typelibrary for Scripting Runtime has the name Scripting (this is the name specified in the type library IDL file, it is not the filename), the guid is {420B2830-E718-11CF-893D-00A0C9054228}, and the version number 1.0. The name of the first typelib wrapper module is comtypes.gen._420B2830_E718_11CF_893D_00A0C9054228_0_1_0 and the name of the second friendly module is comtypes.gen.Scripting.

When you want to freeze your script with py2exe you can ensure that py2exe includes these typelib wrappers by writing:

import comtypes.gen.Scripting

somewhere.

Added in version 1.3.0: The friendly module imports the wrapper module with an abstracted alias __wrapper_module__.

Changed in version 1.4.0: The friendly module defines enumerations from typeinfo of the typelibrary. Prior to this, the friendly module imported everything from the wrapper module, and all names used in enumerations were aliases for ctypes.c_int. Even after version 1.4.0, by modifying the codebase as follows, these names can continue to be used as aliases for c_int rather than as enumerations.

- from comtypes.gen.friendlymodule import TheName
+ from ctypes import c_int as TheName

from comtypes.gen import friendlymodule
- c_int_alias = friendlymodule.TheName
+ c_int_alias = friendlymodule.__wrapper_module__.TheName

- from comtypes.gen import friendlymodule as mod
+ from comtypes.gen.friendlymodule import __wrapper_module__ as mod
c_int_alias = mod.TheName

gen_dir

This variable determines the directory where the typelib wrappers are written to. If it is None, modules are only generated in memory.

comtypes.client.gen_dir is calculated when the comtypes.client module is first imported. It is set to the directory of the comtypes.gen package when this is a valid file system path; otherwise it is set to None.

In a script frozen with py2exe the directory of comtypes.gen is somewhere in a zip-archive, gen_dir is None, and even if tyelib wrappers are created at runtime no attempt is made to write them to the file system. Instead, the modules are generated only in memory.

comtypes.client.gen_dir can also be set to None to prevent writing typelib wrappers to the file system. The downside is that for large type libraries the code generation can take some time.

Examples 

Here are several ways to generate the typelib wrapper module for Scripting Dictionary with the GetModule function:

>>> from comtypes.client import GetModule
>>> GetModule('scrrun.dll')  
<module 'comtypes.gen.Scripting'...>
>>> GetModule(('{420B2830-E718-11CF-893D-00A0C9054228}', 1, 0))  
<module 'comtypes.gen.Scripting'...>

Members such as the first wrapper module, interface classes, coclasses, constants, and enumerations can be referenced from the friendly module generated by calling the GetModule function:

>>> Scripting = GetModule('scrrun.dll')
>>> Scripting.__wrapper_module__  # the first wrapper module  
<module 'comtypes.gen._420B2830_E718_11CF_893D_00A0C9054228_0_1_0'...>
>>> Scripting.IDictionary  # an interface class
<class 'comtypes.gen._420B2830_E718_11CF_893D_00A0C9054228_0_1_0.IDictionary'>
>>> Scripting.Dictionary  # a coclass
<class 'comtypes.gen._420B2830_E718_11CF_893D_00A0C9054228_0_1_0.Dictionary'>
>>> Scripting.BinaryCompare  # a constant
0
>>> Scripting.CompareMethod  # an enumeration
<flag 'CompareMethod'>
>>> Scripting.CompareMethod.BinaryCompare  # a member of the enumeration
<CompareMethod.BinaryCompare: 0>

This code snippet could be used to generate the typelib wrapper module for Scripting Dictionary automatically when your script is run, and would include the module into the exe-file when the script is frozen by py2exe:

>>> import sys
>>> if not hasattr(sys, 'frozen'):  
...     from comtypes.client import GetModule
...     GetModule('scrrun.dll')
...
<module 'comtypes.gen.Scripting'...>
>>> import comtypes.gen.Scripting

Other stuff 

XXX describe logging, gen_dir, wrap, _manage (?)