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Diffstat (limited to 'cloudinit/mergers/__init__.py')
| -rw-r--r-- | cloudinit/mergers/__init__.py | 104 |
1 files changed, 104 insertions, 0 deletions
diff --git a/cloudinit/mergers/__init__.py b/cloudinit/mergers/__init__.py new file mode 100644 index 00000000..b3e728b0 --- /dev/null +++ b/cloudinit/mergers/__init__.py @@ -0,0 +1,104 @@ +# vi: ts=4 expandtab +# +# Copyright (C) 2012 Yahoo! Inc. +# +# Author: Joshua Harlow <harlowja@yahoo-inc.com> +# +# This program is free software: you can redistribute it and/or modify +# it under the terms of the GNU General Public License version 3, as +# published by the Free Software Foundation. +# +# 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/>. + + +from cloudinit import importer +from cloudinit import log as logging +from cloudinit import util + +LOG = logging.getLogger(__name__) + + +class UnknownMerger(object): + # Named differently so auto-method finding + # doesn't pick this up if there is ever a type + # named "unknown" + def _handle_unknown(self, meth_wanted, value, merge_with): + return value + + def merge(self, source, merge_with): + type_name = util.obj_name(source) + type_name = type_name.lower() + method_name = "_on_%s" % (type_name) + meth = None + args = [source, merge_with] + if hasattr(self, method_name): + meth = getattr(self, method_name) + if not meth: + meth = self._handle_unknown + args.insert(0, method_name) + return meth(*args) + + +class LookupMerger(UnknownMerger): + def __init__(self, lookups=None): + UnknownMerger.__init__(self) + if lookups is None: + self._lookups = [] + else: + self._lookups = lookups + + def _handle_unknown(self, meth_wanted, value, merge_with): + meth = None + for merger in self._lookups: + if hasattr(merger, meth_wanted): + # First one that has that method/attr gets to be + # the one that will be called + meth = getattr(merger, meth_wanted) + break + if not meth: + return UnknownMerger._handle_unknown(self, meth_wanted, + value, merge_with) + return meth(value, merge_with) + + +def _extract_merger_names(merge_how): + names = [] + for m_name in merge_how.split("+"): + # Canonicalize the name (so that it can be found + # even when users alter it in various ways... + m_name = m_name.lower().strip() + m_name = m_name.replace(" ", "_") + m_name = m_name.replace("\t", "_") + m_name = m_name.replace("-", "_") + if not m_name: + continue + names.append(m_name) + return names + + +def construct(merge_how, default_classes=None): + mergers = [] + merger_classes = [] + root = LookupMerger(mergers) + for m_name in _extract_merger_names(merge_how): + merger_locs = importer.find_module(m_name, + [__name__], + ['Merger']) + if not merger_locs: + msg = "Could not find merger named %s" % (m_name) + raise ImportError(msg) + else: + mod = importer.import_module(merger_locs[0]) + cls = getattr(mod, 'Merger') + merger_classes.append(cls) + if not merger_classes and default_classes: + merger_classes = default_classes + for m_class in merger_classes: + mergers.append(m_class(root)) + return root
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