## Match a $[HOST] name resolution reference; group 1 is the HOST.
r_resolve = RX.compile(r'\$\[([^]]+)\]')
+def _fmt_path(path):
+ return ' -> '.join(["`%s'" % hop for hop in path])
+
+class AmbiguousOptionError (Exception):
+ def __init__(me, key, patha, vala, pathb, valb):
+ me.key = key
+ me.patha, me.vala = patha, vala
+ me.pathb, me.valb = pathb, valb
+ def __str__(me):
+ return "Ambiguous answer resolving key `%s': " \
+ "path %s yields `%s' but %s yields `%s'" % \
+ (me.key, _fmt_path(me.patha), me.vala, _fmt_path(me.pathb), me.valb)
+
+class InheritanceCycleError (Exception):
+ def __init__(me, key, path):
+ me.key = key
+ me.path = path
+ def __str__(me):
+ return "Found a cycle %s looking up key `%s'" % \
+ (_fmt_path(me.path), me.key)
+
+class MissingKeyException (Exception):
+ def __init__(me, sec, key):
+ me.sec = sec
+ me.key = key
+ def __str__(me):
+ return "Key `%s' not found in section `%s'" % (me.key, me.sec)
+
class MyConfigParser (CP.RawConfigParser):
"""
A more advanced configuration parser.
This version of the method properly handles the @inherit key.
"""
- return CP.RawConfigParser.has_option(me, sec, key) or \
- (CP.RawConfigParser.has_option(me, sec, '@inherit') and
- me.has_option(CP.RawConfigParser.get(me, sec, '@inherit'), key))
+ return key == 'name' or me._get(sec, key)[0] is not None
- def _get(me, basesec, sec, key, resolvep):
+ def _get(me, sec, key, map = None, path = None):
"""
Low-level option-fetching method.
Fetch the value for the named KEY from section SEC, or maybe
- (recursively) the section which SEC inherits from.
+ (recursively) a section which SEC inherits from.
- The result is expanded, by _expend; RESOLVEP is passed to _expand to
- control whether $[...] should be expanded in the result.
+ Returns a pair VALUE, PATH. The value is not expanded; nor do we check
+ for the special `name' key. The caller is expected to do these things.
+ Returns None if no value could be found.
+ """
- The BASESEC is the section for which the original request was made. This
- will be different from SEC if we're recursing up the inheritance chain.
+ ## If we weren't given a memoization map or path, then we'd better make
+ ## one.
+ if map is None: map = {}
+ if path is None: path = []
- We also provide the default value for `name' here.
- """
+ ## If we've been this way before on another pass through then return the
+ ## value we found then. If we're still thinking about it then we've
+ ## found a cycle.
+ path.append(sec)
+ try:
+ threadp, value = map[sec]
+ except KeyError:
+ pass
+ else:
+ if threadp:
+ raise InheritanceCycleError, (key, path)
+
+ ## See whether the answer is ready waiting for us.
try:
- raw = CP.RawConfigParser.get(me, sec, key)
+ v = CP.RawConfigParser.get(me, sec, key)
except CP.NoOptionError:
- if key == 'name':
- raw = basesec
- elif CP.RawConfigParser.has_option(me, sec, '@inherit'):
- raw = me._get(basesec,
- CP.RawConfigParser.get(me, sec, '@inherit'),
- key,
- resolvep)
- else:
- raise
- return me._expand(basesec, raw, resolvep)
+ pass
+ else:
+ p = path[:]
+ path.pop()
+ return v, p
+
+ ## No, apparently, not. Find out our list of parents.
+ try:
+ parents = CP.RawConfigParser.get(me, sec, '@inherit').\
+ replace(',', ' ').split()
+ except CP.NoOptionError:
+ parents = []
+
+ ## Initially we have no idea.
+ value = None
+ winner = None
+
+ ## Go through our parents and ask them what they think.
+ map[sec] = True, None
+ for p in parents:
+
+ ## See whether we get an answer. If not, keep on going.
+ v, pp = me._get(p, key, map, path)
+ if v is None: continue
+
+ ## If we got an answer, check that it matches any previous ones.
+ if value is None:
+ value = v
+ winner = pp
+ elif value != v:
+ raise AmbiguousOptionError, (key, winner, value, pp, v)
+
+ ## That's the best we could manage.
+ path.pop()
+ map[sec] = False, value
+ return value, winner
def get(me, sec, key, resolvep = True):
"""
Retrieve the value of KEY from section SEC.
"""
- return me._get(sec, sec, key, resolvep)
+
+ ## Special handling for the `name' key.
+ if key == 'name':
+ try: value = CP.RawConfigParser.get(me, sec, key)
+ except CP.NoOptionError: value = sec
+ else:
+ value, _ = me._get(sec, key)
+ if value is None:
+ raise MissingKeyException, (sec, key)
+
+ ## Expand the value and return it.
+ return me._expand(sec, value, resolvep)
def items(me, sec, resolvep = True):
"""
This extends the default method by handling the inheritance chain.
"""
+
+ ## Initialize for a depth-first walk of the inheritance graph.
d = {}
+ visited = {}
basesec = sec
- while sec:
- next = None
+ stack = [sec]
+
+ ## Visit nodes, collecting their keys. Don't believe the values:
+ ## resolving inheritance is too hard to do like this.
+ while stack:
+ sec = stack.pop()
+ if sec in visited: continue
+ visited[sec] = True
+
for key, value in CP.RawConfigParser.items(me, sec):
- if key == '@inherit':
- next = value
- elif not key.startswith('@') and key not in d:
- d[key] = me._expand(basesec, value, resolvep)
- sec = next
- return d.items()
+ if key == '@inherit': stack += value.replace(',', ' ').split()
+ else: d[key] = None
+
+ ## Now collect the values for the known keys, one by one.
+ items = []
+ for key in d: items.append((key, me.get(basesec, key, resolvep)))
+
+ ## And we're done.
+ return items
###--------------------------------------------------------------------------
### Command-line handling.
~mdw / tripe / commitdiff