[gnuoy,trivial] Pre-release charmhelper sync

charm-helpers-hooks.yaml

@@ -2,6 +2,7 @@ branch: lp:charm-helpers
 destination: hooks/charmhelpers
 include:
     - core
+    - cli
     - fetch
     - contrib.openstack|inc=*
     - contrib.hahelpers

hooks/charmhelpers/cli/__init__.py

@@ -0,0 +1,195 @@
+# Copyright 2014-2015 Canonical Limited.
+#
+# This file is part of charm-helpers.
+#
+# charm-helpers is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Lesser General Public License version 3 as
+# published by the Free Software Foundation.
+#
+# charm-helpers 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 charm-helpers.  If not, see <http://www.gnu.org/licenses/>.
+
+import inspect
+import argparse
+import sys
+
+from six.moves import zip
+
+from charmhelpers.core import unitdata
+
+
+class OutputFormatter(object):
+    def __init__(self, outfile=sys.stdout):
+        self.formats = (
+            "raw",
+            "json",
+            "py",
+            "yaml",
+            "csv",
+            "tab",
+        )
+        self.outfile = outfile
+
+    def add_arguments(self, argument_parser):
+        formatgroup = argument_parser.add_mutually_exclusive_group()
+        choices = self.supported_formats
+        formatgroup.add_argument("--format", metavar='FMT',
+                                 help="Select output format for returned data, "
+                                      "where FMT is one of: {}".format(choices),
+                                 choices=choices, default='raw')
+        for fmt in self.formats:
+            fmtfunc = getattr(self, fmt)
+            formatgroup.add_argument("-{}".format(fmt[0]),
+                                     "--{}".format(fmt), action='store_const',
+                                     const=fmt, dest='format',
+                                     help=fmtfunc.__doc__)
+
+    @property
+    def supported_formats(self):
+        return self.formats
+
+    def raw(self, output):
+        """Output data as raw string (default)"""
+        if isinstance(output, (list, tuple)):
+            output = '\n'.join(map(str, output))
+        self.outfile.write(str(output))
+
+    def py(self, output):
+        """Output data as a nicely-formatted python data structure"""
+        import pprint
+        pprint.pprint(output, stream=self.outfile)
+
+    def json(self, output):
+        """Output data in JSON format"""
+        import json
+        json.dump(output, self.outfile)
+
+    def yaml(self, output):
+        """Output data in YAML format"""
+        import yaml
+        yaml.safe_dump(output, self.outfile)
+
+    def csv(self, output):
+        """Output data as excel-compatible CSV"""
+        import csv
+        csvwriter = csv.writer(self.outfile)
+        csvwriter.writerows(output)
+
+    def tab(self, output):
+        """Output data in excel-compatible tab-delimited format"""
+        import csv
+        csvwriter = csv.writer(self.outfile, dialect=csv.excel_tab)
+        csvwriter.writerows(output)
+
+    def format_output(self, output, fmt='raw'):
+        fmtfunc = getattr(self, fmt)
+        fmtfunc(output)
+
+
+class CommandLine(object):
+    argument_parser = None
+    subparsers = None
+    formatter = None
+    exit_code = 0
+
+    def __init__(self):
+        if not self.argument_parser:
+            self.argument_parser = argparse.ArgumentParser(description='Perform common charm tasks')
+        if not self.formatter:
+            self.formatter = OutputFormatter()
+            self.formatter.add_arguments(self.argument_parser)
+        if not self.subparsers:
+            self.subparsers = self.argument_parser.add_subparsers(help='Commands')
+
+    def subcommand(self, command_name=None):
+        """
+        Decorate a function as a subcommand. Use its arguments as the
+        command-line arguments"""
+        def wrapper(decorated):
+            cmd_name = command_name or decorated.__name__
+            subparser = self.subparsers.add_parser(cmd_name,
+                                                   description=decorated.__doc__)
+            for args, kwargs in describe_arguments(decorated):
+                subparser.add_argument(*args, **kwargs)
+            subparser.set_defaults(func=decorated)
+            return decorated
+        return wrapper
+
+    def test_command(self, decorated):
+        """
+        Subcommand is a boolean test function, so bool return values should be
+        converted to a 0/1 exit code.
+        """
+        decorated._cli_test_command = True
+        return decorated
+
+    def no_output(self, decorated):
+        """
+        Subcommand is not expected to return a value, so don't print a spurious None.
+        """
+        decorated._cli_no_output = True
+        return decorated
+
+    def subcommand_builder(self, command_name, description=None):
+        """
+        Decorate a function that builds a subcommand. Builders should accept a
+        single argument (the subparser instance) and return the function to be
+        run as the command."""
+        def wrapper(decorated):
+            subparser = self.subparsers.add_parser(command_name)
+            func = decorated(subparser)
+            subparser.set_defaults(func=func)
+            subparser.description = description or func.__doc__
+        return wrapper
+
+    def run(self):
+        "Run cli, processing arguments and executing subcommands."
+        arguments = self.argument_parser.parse_args()
+        argspec = inspect.getargspec(arguments.func)
+        vargs = []
+        kwargs = {}
+        for arg in argspec.args:
+            vargs.append(getattr(arguments, arg))
+        if argspec.varargs:
+            vargs.extend(getattr(arguments, argspec.varargs))
+        if argspec.keywords:
+            for kwarg in argspec.keywords.items():
+                kwargs[kwarg] = getattr(arguments, kwarg)
+        output = arguments.func(*vargs, **kwargs)
+        if getattr(arguments.func, '_cli_test_command', False):
+            self.exit_code = 0 if output else 1
+            output = ''
+        if getattr(arguments.func, '_cli_no_output', False):
+            output = ''
+        self.formatter.format_output(output, arguments.format)
+        if unitdata._KV:
+            unitdata._KV.flush()
+
+
+cmdline = CommandLine()
+
+
+def describe_arguments(func):
+    """
+    Analyze a function's signature and return a data structure suitable for
+    passing in as arguments to an argparse parser's add_argument() method."""
+
+    argspec = inspect.getargspec(func)
+    # we should probably raise an exception somewhere if func includes **kwargs
+    if argspec.defaults:
+        positional_args = argspec.args[:-len(argspec.defaults)]
+        keyword_names = argspec.args[-len(argspec.defaults):]
+        for arg, default in zip(keyword_names, argspec.defaults):
+            yield ('--{}'.format(arg),), {'default': default}
+    else:
+        positional_args = argspec.args
+
+    for arg in positional_args:
+        yield (arg,), {}
+    if argspec.varargs:
+        yield (argspec.varargs,), {'nargs': '*'}

hooks/charmhelpers/cli/benchmark.py

@@ -0,0 +1,36 @@
+# Copyright 2014-2015 Canonical Limited.
+#
+# This file is part of charm-helpers.
+#
+# charm-helpers is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Lesser General Public License version 3 as
+# published by the Free Software Foundation.
+#
+# charm-helpers 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 charm-helpers.  If not, see <http://www.gnu.org/licenses/>.
+
+from . import cmdline
+from charmhelpers.contrib.benchmark import Benchmark
+
+
+@cmdline.subcommand(command_name='benchmark-start')
+def start():
+    Benchmark.start()
+
+
+@cmdline.subcommand(command_name='benchmark-finish')
+def finish():
+    Benchmark.finish()
+
+
+@cmdline.subcommand_builder('benchmark-composite', description="Set the benchmark composite score")
+def service(subparser):
+    subparser.add_argument("value", help="The composite score.")
+    subparser.add_argument("units", help="The units the composite score represents, i.e., 'reads/sec'.")
+    subparser.add_argument("direction", help="'asc' if a lower score is better, 'desc' if a higher score is better.")
+    return Benchmark.set_composite_score

hooks/charmhelpers/cli/commands.py

@@ -0,0 +1,32 @@
+# Copyright 2014-2015 Canonical Limited.
+#
+# This file is part of charm-helpers.
+#
+# charm-helpers is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Lesser General Public License version 3 as
+# published by the Free Software Foundation.
+#
+# charm-helpers 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 charm-helpers.  If not, see <http://www.gnu.org/licenses/>.
+
+"""
+This module loads sub-modules into the python runtime so they can be
+discovered via the inspect module. In order to prevent flake8 from (rightfully)
+telling us these are unused modules, throw a ' # noqa' at the end of each import
+so that the warning is suppressed.
+"""
+
+from . import CommandLine  # noqa
+
+"""
+Import the sub-modules which have decorated subcommands to register with chlp.
+"""
+import host  # noqa
+import benchmark  # noqa
+import unitdata  # noqa
+from charmhelpers.core import hookenv  # noqa

hooks/charmhelpers/cli/host.py

@@ -0,0 +1,31 @@
+# Copyright 2014-2015 Canonical Limited.
+#
+# This file is part of charm-helpers.
+#
+# charm-helpers is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Lesser General Public License version 3 as
+# published by the Free Software Foundation.
+#
+# charm-helpers 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 charm-helpers.  If not, see <http://www.gnu.org/licenses/>.
+
+from . import cmdline
+from charmhelpers.core import host
+
+
+@cmdline.subcommand()
+def mounts():
+    "List mounts"
+    return host.mounts()
+
+
+@cmdline.subcommand_builder('service', description="Control system services")
+def service(subparser):
+    subparser.add_argument("action", help="The action to perform (start, stop, etc...)")
+    subparser.add_argument("service_name", help="Name of the service to control")
+    return host.service

hooks/charmhelpers/cli/unitdata.py

@@ -0,0 +1,39 @@
+# Copyright 2014-2015 Canonical Limited.
+#
+# This file is part of charm-helpers.
+#
+# charm-helpers is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Lesser General Public License version 3 as
+# published by the Free Software Foundation.
+#
+# charm-helpers 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 charm-helpers.  If not, see <http://www.gnu.org/licenses/>.
+
+from . import cmdline
+from charmhelpers.core import unitdata
+
+
+@cmdline.subcommand_builder('unitdata', description="Store and retrieve data")
+def unitdata_cmd(subparser):
+    nested = subparser.add_subparsers()
+    get_cmd = nested.add_parser('get', help='Retrieve data')
+    get_cmd.add_argument('key', help='Key to retrieve the value of')
+    get_cmd.set_defaults(action='get', value=None)
+    set_cmd = nested.add_parser('set', help='Store data')
+    set_cmd.add_argument('key', help='Key to set')
+    set_cmd.add_argument('value', help='Value to store')
+    set_cmd.set_defaults(action='set')
+
+    def _unitdata_cmd(action, key, value):
+        if action == 'get':
+            return unitdata.kv().get(key)
+        elif action == 'set':
+            unitdata.kv().set(key, value)
+            unitdata.kv().flush()
+            return ''
+    return _unitdata_cmd

hooks/charmhelpers/contrib/openstack/context.py

@@ -1051,13 +1051,22 @@ class SubordinateConfigContext(OSContextGenerator):
         :param config_file : Service's config file to query sections
         :param interface   : Subordinate interface to inspect
         """
-        self.service = service
         self.config_file = config_file
-        self.interface = interface
+        if isinstance(service, list):
+            self.services = service
+        else:
+            self.services = [service]
+        if isinstance(interface, list):
+            self.interfaces = interface
+        else:
+            self.interfaces = [interface]
 
     def __call__(self):
         ctxt = {'sections': {}}
-        for rid in relation_ids(self.interface):
+        rids = []
+        for interface in self.interfaces:
+            rids.extend(relation_ids(interface))
+        for rid in rids:
             for unit in related_units(rid):
                 sub_config = relation_get('subordinate_configuration',
                                           rid=rid, unit=unit)
@@ -1069,29 +1078,32 @@ class SubordinateConfigContext(OSContextGenerator):
                             'setting from %s' % rid, level=ERROR)
                         continue
 
-                    if self.service not in sub_config:
+                    for service in self.services:
-                        log('Found subordinate_config on %s but it contained'
+                        if service not in sub_config:
-                            'nothing for %s service' % (rid, self.service),
+                            log('Found subordinate_config on %s but it contained'
-                            level=INFO)
+                                'nothing for %s service' % (rid, service),
-                        continue
+                                level=INFO)
+                            continue
 
-                    sub_config = sub_config[self.service]
+                        sub_config = sub_config[service]
-                    if self.config_file not in sub_config:
+                        if self.config_file not in sub_config:
-                        log('Found subordinate_config on %s but it contained'
+                            log('Found subordinate_config on %s but it contained'
-                            'nothing for %s' % (rid, self.config_file),
+                                'nothing for %s' % (rid, self.config_file),
-                            level=INFO)
+                                level=INFO)
-                        continue
+                            continue
-
-                    sub_config = sub_config[self.config_file]
-                    for k, v in six.iteritems(sub_config):
-                        if k == 'sections':
-                            for section, config_dict in six.iteritems(v):
-                                log("adding section '%s'" % (section),
-                                    level=DEBUG)
-                                ctxt[k][section] = config_dict
-                        else:
-                            ctxt[k] = v
 
+                        sub_config = sub_config[self.config_file]
+                        for k, v in six.iteritems(sub_config):
+                            if k == 'sections':
+                                for section, config_list in six.iteritems(v):
+                                    log("adding section '%s'" % (section),
+                                        level=DEBUG)
+                                    if ctxt[k].get(section):
+                                        ctxt[k][section].extend(config_list)
+                                    else:
+                                        ctxt[k][section] = config_list
+                            else:
+                                ctxt[k] = v
         log("%d section(s) found" % (len(ctxt['sections'])), level=DEBUG)
         return ctxt
 

hooks/charmhelpers/core/files.py

@@ -0,0 +1,45 @@
+#!/usr/bin/env python
+# -*- coding: utf-8 -*-
+
+# Copyright 2014-2015 Canonical Limited.
+#
+# This file is part of charm-helpers.
+#
+# charm-helpers is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Lesser General Public License version 3 as
+# published by the Free Software Foundation.
+#
+# charm-helpers 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 charm-helpers.  If not, see <http://www.gnu.org/licenses/>.
+
+__author__ = 'Jorge Niedbalski <niedbalski@ubuntu.com>'
+
+import os
+import subprocess
+
+
+def sed(filename, before, after, flags='g'):
+    """
+    Search and replaces the given pattern on filename.
+
+    :param filename: relative or absolute file path.
+    :param before: expression to be replaced (see 'man sed')
+    :param after: expression to replace with (see 'man sed')
+    :param flags: sed-compatible regex flags in example, to make
+    the  search and replace case insensitive, specify ``flags="i"``.
+    The ``g`` flag is always specified regardless, so you do not
+    need to remember to include it when overriding this parameter.
+    :returns: If the sed command exit code was zero then return,
+    otherwise raise CalledProcessError.
+    """
+    expression = r's/{0}/{1}/{2}'.format(before,
+                                         after, flags)
+
+    return subprocess.check_call(["sed", "-i", "-r", "-e",
+                                  expression,
+                                  os.path.expanduser(filename)])

hooks/charmhelpers/core/hookenv.py

@@ -34,6 +34,23 @@ import errno
 import tempfile
 from subprocess import CalledProcessError
 
+try:
+    from charmhelpers.cli import cmdline
+except ImportError as e:
+    # due to the anti-pattern of partially synching charmhelpers directly
+    # into charms, it's possible that charmhelpers.cli is not available;
+    # if that's the case, they don't really care about using the cli anyway,
+    # so mock it out
+    if str(e) == 'No module named cli':
+        class cmdline(object):
+            @classmethod
+            def subcommand(cls, *args, **kwargs):
+                def _wrap(func):
+                    return func
+                return _wrap
+    else:
+        raise
+
 import six
 if not six.PY3:
     from UserDict import UserDict
@@ -173,9 +190,20 @@ def relation_type():
     return os.environ.get('JUJU_RELATION', None)
 
 
-def relation_id():
+@cmdline.subcommand()
-    """The relation ID for the current relation hook"""
+@cached
-    return os.environ.get('JUJU_RELATION_ID', None)
+def relation_id(relation_name=None, service_or_unit=None):
+    """The relation ID for the current or a specified relation"""
+    if not relation_name and not service_or_unit:
+        return os.environ.get('JUJU_RELATION_ID', None)
+    elif relation_name and service_or_unit:
+        service_name = service_or_unit.split('/')[0]
+        for relid in relation_ids(relation_name):
+            remote_service = remote_service_name(relid)
+            if remote_service == service_name:
+                return relid
+    else:
+        raise ValueError('Must specify neither or both of relation_name and service_or_unit')
 
 
 def local_unit():
@@ -188,14 +216,27 @@ def remote_unit():
     return os.environ.get('JUJU_REMOTE_UNIT', None)
 
 
+@cmdline.subcommand()
 def service_name():
     """The name service group this unit belongs to"""
     return local_unit().split('/')[0]
 
 
+@cmdline.subcommand()
+@cached
+def remote_service_name(relid=None):
+    """The remote service name for a given relation-id (or the current relation)"""
+    if relid is None:
+        unit = remote_unit()
+    else:
+        units = related_units(relid)
+        unit = units[0] if units else None
+    return unit.split('/')[0] if unit else None
+
+
 def hook_name():
     """The name of the currently executing hook"""
-    return os.path.basename(sys.argv[0])
+    return os.environ.get('JUJU_HOOK_NAME', os.path.basename(sys.argv[0]))
 
 
 class Config(dict):
@@ -468,6 +509,63 @@ def relation_types():
     return rel_types
 
 
+@cached
+def relation_to_interface(relation_name):
+    """
+    Given the name of a relation, return the interface that relation uses.
+
+    :returns: The interface name, or ``None``.
+    """
+    return relation_to_role_and_interface(relation_name)[1]
+
+
+@cached
+def relation_to_role_and_interface(relation_name):
+    """
+    Given the name of a relation, return the role and the name of the interface
+    that relation uses (where role is one of ``provides``, ``requires``, or ``peer``).
+
+    :returns: A tuple containing ``(role, interface)``, or ``(None, None)``.
+    """
+    _metadata = metadata()
+    for role in ('provides', 'requires', 'peer'):
+        interface = _metadata.get(role, {}).get(relation_name, {}).get('interface')
+        if interface:
+            return role, interface
+    return None, None
+
+
+@cached
+def role_and_interface_to_relations(role, interface_name):
+    """
+    Given a role and interface name, return a list of relation names for the
+    current charm that use that interface under that role (where role is one
+    of ``provides``, ``requires``, or ``peer``).
+
+    :returns: A list of relation names.
+    """
+    _metadata = metadata()
+    results = []
+    for relation_name, relation in _metadata.get(role, {}).items():
+        if relation['interface'] == interface_name:
+            results.append(relation_name)
+    return results
+
+
+@cached
+def interface_to_relations(interface_name):
+    """
+    Given an interface, return a list of relation names for the current
+    charm that use that interface.
+
+    :returns: A list of relation names.
+    """
+    results = []
+    for role in ('provides', 'requires', 'peer'):
+        results.extend(role_and_interface_to_relations(role, interface_name))
+    return results
+
+
 @cached
 def charm_name():
     """Get the name of the current charm as is specified on metadata.yaml"""
@@ -644,6 +742,21 @@ def action_fail(message):
     subprocess.check_call(['action-fail', message])
 
 
+def action_name():
+    """Get the name of the currently executing action."""
+    return os.environ.get('JUJU_ACTION_NAME')
+
+
+def action_uuid():
+    """Get the UUID of the currently executing action."""
+    return os.environ.get('JUJU_ACTION_UUID')
+
+
+def action_tag():
+    """Get the tag for the currently executing action."""
+    return os.environ.get('JUJU_ACTION_TAG')
+
+
 def status_set(workload_state, message):
     """Set the workload state with a message
 

hooks/charmhelpers/core/unitdata.py

@@ -152,6 +152,7 @@ associated to the hookname.
 import collections
 import contextlib
 import datetime
+import itertools
 import json
 import os
 import pprint
@@ -164,8 +165,7 @@ __author__ = 'Kapil Thangavelu <kapil.foss@gmail.com>'
 class Storage(object):
     """Simple key value database for local unit state within charms.
 
-    Modifications are automatically committed at hook exit. That's
+    Modifications are not persisted unless :meth:`flush` is called.
-    currently regardless of exit code.
 
     To support dicts, lists, integer, floats, and booleans values
     are automatically json encoded/decoded.
@@ -173,8 +173,11 @@ class Storage(object):
     def __init__(self, path=None):
         self.db_path = path
         if path is None:
-            self.db_path = os.path.join(
+            if 'UNIT_STATE_DB' in os.environ:
-                os.environ.get('CHARM_DIR', ''), '.unit-state.db')
+                self.db_path = os.environ['UNIT_STATE_DB']
+            else:
+                self.db_path = os.path.join(
+                    os.environ.get('CHARM_DIR', ''), '.unit-state.db')
         self.conn = sqlite3.connect('%s' % self.db_path)
         self.cursor = self.conn.cursor()
         self.revision = None
@@ -189,15 +192,8 @@ class Storage(object):
         self.conn.close()
         self._closed = True
 
-    def _scoped_query(self, stmt, params=None):
-        if params is None:
-            params = []
-        return stmt, params
-
     def get(self, key, default=None, record=False):
-        self.cursor.execute(
+        self.cursor.execute('select data from kv where key=?', [key])
-            *self._scoped_query(
-                'select data from kv where key=?', [key]))
         result = self.cursor.fetchone()
         if not result:
             return default
@@ -206,33 +202,81 @@ class Storage(object):
         return json.loads(result[0])
 
     def getrange(self, key_prefix, strip=False):
-        stmt = "select key, data from kv where key like '%s%%'" % key_prefix
+        """
-        self.cursor.execute(*self._scoped_query(stmt))
+        Get a range of keys starting with a common prefix as a mapping of
+        keys to values.
+
+        :param str key_prefix: Common prefix among all keys
+        :param bool strip: Optionally strip the common prefix from the key
+            names in the returned dict
+        :return dict: A (possibly empty) dict of key-value mappings
+        """
+        self.cursor.execute("select key, data from kv where key like ?",
+                            ['%s%%' % key_prefix])
         result = self.cursor.fetchall()
 
         if not result:
-            return None
+            return {}
         if not strip:
             key_prefix = ''
         return dict([
             (k[len(key_prefix):], json.loads(v)) for k, v in result])
 
     def update(self, mapping, prefix=""):
+        """
+        Set the values of multiple keys at once.
+
+        :param dict mapping: Mapping of keys to values
+        :param str prefix: Optional prefix to apply to all keys in `mapping`
+            before setting
+        """
         for k, v in mapping.items():
             self.set("%s%s" % (prefix, k), v)
 
     def unset(self, key):
+        """
+        Remove a key from the database entirely.
+        """
         self.cursor.execute('delete from kv where key=?', [key])
         if self.revision and self.cursor.rowcount:
             self.cursor.execute(
                 'insert into kv_revisions values (?, ?, ?)',
                 [key, self.revision, json.dumps('DELETED')])
 
+    def unsetrange(self, keys=None, prefix=""):
+        """
+        Remove a range of keys starting with a common prefix, from the database
+        entirely.
+
+        :param list keys: List of keys to remove.
+        :param str prefix: Optional prefix to apply to all keys in ``keys``
+            before removing.
+        """
+        if keys is not None:
+            keys = ['%s%s' % (prefix, key) for key in keys]
+            self.cursor.execute('delete from kv where key in (%s)' % ','.join(['?'] * len(keys)), keys)
+            if self.revision and self.cursor.rowcount:
+                self.cursor.execute(
+                    'insert into kv_revisions values %s' % ','.join(['(?, ?, ?)'] * len(keys)),
+                    list(itertools.chain.from_iterable((key, self.revision, json.dumps('DELETED')) for key in keys)))
+        else:
+            self.cursor.execute('delete from kv where key like ?',
+                                ['%s%%' % prefix])
+            if self.revision and self.cursor.rowcount:
+                self.cursor.execute(
+                    'insert into kv_revisions values (?, ?, ?)',
+                    ['%s%%' % prefix, self.revision, json.dumps('DELETED')])
+
     def set(self, key, value):
+        """
+        Set a value in the database.
+
+        :param str key: Key to set the value for
+        :param value: Any JSON-serializable value to be set
+        """
         serialized = json.dumps(value)
 
-        self.cursor.execute(
+        self.cursor.execute('select data from kv where key=?', [key])
-            'select data from kv where key=?', [key])
         exists = self.cursor.fetchone()
 
         # Skip mutations to the same value