# ###########################################################################
#
# This file is part of Taurus
#
# http://taurus-scada.org
#
# Copyright 2011 CELLS / ALBA Synchrotron, Bellaterra, Spain
#
# Taurus is free software: you can redistribute it and/or modify
# it under the terms of the GNU Lesser General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# Taurus 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 Lesser General Public License for more details.
#
# You should have received a copy of the GNU Lesser General Public License
# along with Taurus. If not, see <http://www.gnu.org/licenses/>.
#
# ###########################################################################
"""
This module provides LazyModule for loading plugin modules in lazy way -
only when members of actual plugin are requested.
"""
__all__ = ["LazyModule"]
from types import ModuleType
import sys
from taurus import warning, info
[docs]class LazyModule(ModuleType):
"""It provides a ModuleType object that acts as a placeholder for modules
registered via entry-points. It replaces the actual module without actually
importing it until a member of the module is requested, which automatically
triggers the load of the entry-point and the substitution of this
placeholder by the actual module
"""
def __init__(self, name, package, entry_point):
"""
:param name: name of the module
:param package: name of the package to which the module belongs
:param entry_point: entry-point for the module
"""
super(LazyModule, self).__init__(name)
self.__package__ = package
self.ep = entry_point
def __getattr__(self, member):
try:
mod = self.ep.load()
# Replace lazy module with actual module for package
setattr(sys.modules[self.__package__], self.__name__, mod)
# Replace lazy module with actual module in sys.modules
modname = "%s.%s" % (self.__package__, self.__name__)
sys.modules[modname] = mod
except Exception as e:
warning('Could not load plugin "%s". Reason: %s', self.ep.name, e)
return None
return getattr(mod, member)
[docs] @staticmethod
def import_ep(name, package, entry_point):
"""
Lazily imports a module defined in an entry point. The LazyModule is
inserted in sys.modules as <package>.<name>
:param name: name of the module
:param package: name of the package to which the module belongs
:param entry_point: entry-point for a module
:return: A LazyModule object
"""
m = LazyModule(name, package, entry_point)
setattr(sys.modules[package], name, m)
modname = "{}.{}".format(package, name)
sys.modules[modname] = m
info(
'Plugin "%s" lazy-loaded as "%s"', entry_point.module_name, modname
)
return m