mmgen-wallet/mmgen/base_obj.py

#!/usr/bin/env python3
#
# mmgen = Multi-Mode GENerator, command-line Bitcoin cold storage solution
# Copyright (C)2013-2020 The MMGen Project <mmgen@tuta.io>
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.

"""
base_obj.py: base objects with no internal imports for the MMGen suite
"""

class AttrCtrl:
	"""
	After instance is locked, forbid setting any attribute if the attribute is not present
	in either the class or instance dict.

	If _use_class_attr is True, ensure that attribute's type matches that of the class
	attribute, unless the class attribute is set to None, in which case no type checking
	is performed.
	"""
	_lock = False
	_use_class_attr = False

	def lock(self):
		self._lock = True

	def __setattr__(self,name,value):
		if self._lock:
			def do_error(name,value,ref_val):
				raise AttributeError(
					f'{value!r}: invalid value for attribute {name!r}'
					+ ' of {} object (must be of type {}, not {})'.format(
						type(self).__name__,
						type(ref_val).__name__,
						type(value).__name__ ) )

			if not hasattr(self,name):
				raise AttributeError(f'{type(self).__name__} object has no attribute {name!r}')

			ref_val = getattr(type(self),name) if self._use_class_attr else getattr(self,name)

			if (ref_val is not None) and not isinstance(value,type(ref_val)):
				do_error(name,value,ref_val)

		return object.__setattr__(self,name,value)

	def __delattr__(self,name,value):
		raise AttributeError('attribute cannot be deleted')

class Lockable(AttrCtrl):
	"""
	After instance is locked, its attributes become read-only, with the following exceptions:
	  - if the attribute's name is in _set_ok, attr can be set once after locking, if unset
	  - if the attribute's name is in _reset_ok, read-only restrictions are bypassed and only
	    AttrCtrl checking is performed

	To determine whether an attribute is set, it's matched against either None or the class attribute,
	if _use_class_attr is True
	"""
	_set_ok = ()
	_reset_ok = ()

	def __setattr__(self,name,value):
		if self._lock and hasattr(self,name):
			if name not in (self._set_ok + self._reset_ok):
				raise AttributeError(f'attribute {name!r} of {type(self).__name__} object is read-only')
			elif name not in self._reset_ok:
				#print(self.__dict__)
				if not (
					getattr(self,name) is None or
					( self._use_class_attr and name not in self.__dict__ ) ):
					raise AttributeError(
						f'attribute {name!r} of {type(self).__name__} object is already set,'
						+ ' and resetting is forbidden' )
			# name is in (_set_ok + _reset_ok) -- allow name to be in both lists

		return AttrCtrl.__setattr__(self,name,value)