Geografic-Information-System/lib/python/pydispatch/robustapply.py

"""Robust apply mechanism

Provides a function "call", which can sort out
what arguments a given callable object can take,
and subset the given arguments to match only
those which are acceptable.
"""
import sys
if sys.hexversion >= 0x3000000:
    im_func = '__func__'
    im_self = '__self__'
    im_code = '__code__'
    func_code = '__code__'
else:
    im_func = 'im_func'
    im_self = 'im_self'
    im_code = 'im_code'
    func_code = 'func_code'

def function( receiver ):
	"""Get function-like callable object for given receiver

	returns (function_or_method, codeObject, fromMethod)

	If fromMethod is true, then the callable already
	has its first argument bound
	"""
	if hasattr(receiver, '__call__'):
		# Reassign receiver to the actual method that will be called.
		if hasattr( receiver.__call__, im_func) or hasattr( receiver.__call__, im_code):
			receiver = receiver.__call__
	if hasattr( receiver, im_func ):
		# an instance-method...
		return receiver, getattr(getattr(receiver, im_func), func_code), 1
	elif not hasattr( receiver, func_code):
		raise ValueError('unknown reciever type %s %s'%(receiver, type(receiver)))
	return receiver, getattr(receiver,func_code), 0

def robustApply(receiver, *arguments, **named):
	"""Call receiver with arguments and an appropriate subset of named
	"""
	receiver, codeObject, startIndex = function( receiver )
	acceptable = codeObject.co_varnames[startIndex+len(arguments):codeObject.co_argcount]
	for name in codeObject.co_varnames[startIndex:startIndex+len(arguments)]:
		if name in named:
			raise TypeError(
				"""Argument %r specified both positionally and as a keyword for calling %r"""% (
					name, receiver,
				)
			)
	if not (codeObject.co_flags & 8):
		# fc does not have a **kwds type parameter, therefore 
		# remove unacceptable arguments.
		for arg in named.keys():
			if arg not in acceptable:
				del named[arg]
	return receiver(*arguments, **named)