Re: using decorators for api calls

Niki Spahiev <niki@xxxxxxxxxx> writes:

> Thomas Heller wrote:
>> I've been playing with Python 2.4 decorators again.
>> I found a solution which lets us write compact code, here are two examples:
>> @ stdcall("user32", nonzero, "FindWindowW", c_wchar_p, c_wchar_p)
>> def FindWindow(classname=None, windowname=None):
>>     return _call_(classname, windowname)
>
> I would prefer this empty function to be:
>
> def FindWindow(classname=None, windowname=None):
>      "doc"
>
> and such empty code objects to be replaced by FFI call.

I have some code that does this, although it's not nice imo.

The problem is that the decorator must create a function like this for
the above, given only the function object of the FindWindow above:

def somefunc(classname=None, windowname=None):
    return _call_(classname, windowname)

My code uses the inspect module to build a source code string containing
the 'somefunc', which is then exec'd, the somefunc function object
retrieved, and some properties like func_code and func_defaults are then
used to create a new function with new.function.

If someone finds an easier way, please speak up - I'll append the code I
have written (this code uses _api_ instead of _call_).

Thomas
--
import new

def _create_func_codestring(func, name):
    # given a function object <func>, build the source code for another
    # function, having the same argument list, and a function body
    # which contains a call to an _api_ function.
    # Assuming the <func> has this definition:
    #   def func(first, second="spam", third=42):
    #       ....
    # a string containing the following code is returned:
    #   def <name>(first, second="spam", third=42):
    #       return _api_(first, second, third)
    import inspect
    args = inspect.getargspec(func)
    if args[2]:
        raise TypeError, "function argument list cannot contain ** argument"

    argnames = args[0]
    defaults = args[-1]

    if not defaults:
        if args[1]:
            argnames.append("*%s" % args[1])
        argnames = ", ".join(argnames)
        return "def %s(%s): return _api_(%s)" % (name, argnames, argnames)

    first_list = ", ".join(argnames)

    args = argnames[:-len(defaults)]
    args.extend( ["%s=%r" % t for t in zip(argnames[-len(defaults):], 
defaults)] )
    args = ", ".join(args)

    return """def %s(%s): return _api_(%s)""" % (name, args, first_list)

def _decorate_with_api_global(func, call_api):
    # return a new function derived from <func>, inserting an '_api_'
    # symbol into the function globals, which is bound to the
    # <call_api> object.
    #
    # If the body of <func> is empty, a new function body is created,
    # which simply calls the _api_ object with all parameters passed to <func>.
    if len(func.func_code.co_code) == 4:
        code_string = _create_func_codestring(func, func.func_name)
        d = {}
        exec code_string in d
        func = d[func.func_name]
    func_globals = {"_api_": call_api}
    func_globals.update(func.func_globals)
    return new.function(func.func_code,
                        func_globals,
                        func.func_name,
                        func.func_defaults)




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