def determine_wildcard(extension=None, file_type=None):
	"""
	Assemble a wildcard string of the form:
		[[file_type ](*.extension)|*.extension|]<all_files>
	"""

	all_files = 'All files|*'

	if extension is not None:
		if '|' in extension:
			raise ValueError(extension)

		if file_type is not None:
			if '|' in file_type:
				raise ValueError(file_type)

			wildcard = '{0} (*.{1})|*.{1}|{2}'.format(file_type, extension, all_files)
		else:
			wildcard = '(*.{0})|*.{0}|{1}'.format(extension, all_files)
	else:
		wildcard = all_files

	return wildcard