diff options
Diffstat (limited to 'ipalib/base.py')
| -rw-r--r-- | ipalib/base.py | 240 |
1 files changed, 239 insertions, 1 deletions
diff --git a/ipalib/base.py b/ipalib/base.py index e427b747e..e3d08208c 100644 --- a/ipalib/base.py +++ b/ipalib/base.py @@ -23,7 +23,7 @@ Low-level functions and abstract base classes. import re from constants import NAME_REGEX, NAME_ERROR -from constants import TYPE_ERROR, SET_ERROR, DEL_ERROR +from constants import TYPE_ERROR, SET_ERROR, DEL_ERROR, OVERRIDE_ERROR class ReadOnly(object): @@ -189,6 +189,10 @@ def check_name(name): """ Verify that ``name`` is suitable for a `NameSpace` member name. + In short, ``name`` must be a valid lower-case Python identifier that + neither starts nor ends with an underscore. Otherwise an exception is + raised. + This function will raise a ``ValueError`` if ``name`` does not match the `constants.NAME_REGEX` regular expression. For example: @@ -223,3 +227,237 @@ def check_name(name): NAME_ERROR % (NAME_REGEX, name) ) return name + + +class NameSpace(ReadOnly): + """ + A read-only name-space with handy container behaviours. + + A `NameSpace` instance is an ordered, immutable mapping object whose values + can also be accessed as attributes. A `NameSpace` instance is constructed + from an iterable providing its *members*, which are simply arbitrary objects + with a ``name`` attribute whose value: + + 1. Is unique among the members + + 2. Passes the `check_name()` function + + Beyond that, no restrictions are placed on the members: they can be + classes or instances, and of any type. + + The members can be accessed as attributes on the `NameSpace` instance or + through a dictionary interface. For example, say we create a `NameSpace` + instance from a list containing a single member, like this: + + >>> class my_member(object): + ... name = 'my_name' + ... + >>> namespace = NameSpace([my_member]) + >>> namespace + NameSpace(<1 member>, sort=True) + >>> my_member is namespace.my_name # As an attribute + True + >>> my_member is namespace['my_name'] # As dictionary item + True + + For a more detailed example, say we create a `NameSpace` instance from a + generator like this: + + >>> class Member(object): + ... def __init__(self, i): + ... self.i = i + ... self.name = 'member%d' % i + ... def __repr__(self): + ... return 'Member(%d)' % self.i + ... + >>> ns = NameSpace(Member(i) for i in xrange(3)) + >>> ns + NameSpace(<3 members>, sort=True) + + As above, the members can be accessed as attributes and as dictionary items: + + >>> ns.member0 is ns['member0'] + True + >>> ns.member1 is ns['member1'] + True + >>> ns.member2 is ns['member2'] + True + + Members can also be accessed by index and by slice. For example: + + >>> ns[0] + Member(0) + >>> ns[-1] + Member(2) + >>> ns[1:] + (Member(1), Member(2)) + + (Note that slicing a `NameSpace` returns a ``tuple``.) + + `NameSpace` instances provide standard container emulation for membership + testing, counting, and iteration. For example: + + >>> 'member3' in ns # Is there a member named 'member3'? + False + >>> 'member2' in ns # But there is a member named 'member2' + True + >>> len(ns) # The number of members + 3 + >>> list(ns) # Iterate through the member names + ['member0', 'member1', 'member2'] + + Although not a standard container feature, the `NameSpace.__call__()` method + provides a convenient (and efficient) way to iterate through the members, + like an ordered version of the ``dict.itervalues()`` method. For example: + + >>> list(ns[name] for name in ns) # One way to do it + [Member(0), Member(1), Member(2)] + >>> list(ns()) # A more efficient, less verbose way to do it + [Member(0), Member(1), Member(2)] + + As another convenience, the `NameSpace.__todict__()` method will return copy + of the ``dict`` mapping the member names to the members. For example: + + >>> ns.__todict__() + {'member1': Member(1), 'member0': Member(0), 'member2': Member(2)} + + + `NameSpace.__init__()` locks the instance, so `NameSpace` instances are + read-only from the get-go. For example: + + >>> ns.member3 = Member(3) # Lets add that missing 'member3' + Traceback (most recent call last): + ... + AttributeError: locked: cannot set NameSpace.member3 to Member(3) + + (For information on the locking protocol, see the `ReadOnly` class, of which + `NameSpace` is a subclass.) + + By default the members will be sorted alphabetically by the member name. + For example: + + >>> sorted_ns = NameSpace([Member(7), Member(3), Member(5)]) + >>> sorted_ns + NameSpace(<3 members>, sort=True) + >>> list(sorted_ns) + ['member3', 'member5', 'member7'] + >>> sorted_ns[0] + Member(3) + + But if the instance is created with the ``sort=False`` keyword argument, the + original order of the members is preserved. For example: + + >>> unsorted_ns = NameSpace([Member(7), Member(3), Member(5)], sort=False) + >>> unsorted_ns + NameSpace(<3 members>, sort=False) + >>> list(unsorted_ns) + ['member7', 'member3', 'member5'] + >>> unsorted_ns[0] + Member(7) + + The `NameSpace` class is used in many places throughout freeIPA. For a few + examples, see the `plugable.API` and the `frontend.Command` classes. + """ + + def __init__(self, members, sort=True): + """ + :param members: An iterable providing the members. + :param sort: Whether to sort the members by member name. + """ + if type(sort) is not bool: + raise TypeError( + TYPE_ERROR % ('sort', bool, sort, type(sort)) + ) + self.__sort = sort + if sort: + self.__members = tuple( + sorted(members, key=lambda m: m.name) + ) + else: + self.__members = tuple(members) + self.__names = tuple(m.name for m in self.__members) + self.__map = dict() + for member in self.__members: + name = check_name(member.name) + if name in self.__map: + raise AttributeError(OVERRIDE_ERROR % + (self.__class__.__name__, name, self.__map[name], member) + ) + assert not hasattr(self, name), 'Ouch! Has attribute %r' % name + self.__map[name] = member + setattr(self, name, member) + lock(self) + + def __len__(self): + """ + Return the number of members. + """ + return len(self.__members) + + def __iter__(self): + """ + Iterate through the member names. + + If this instance was created with ``sort=False``, the names will be in + the same order as the members were passed to the constructor; otherwise + the names will be in alphabetical order (which is the default). + + This method is like an ordered version of ``dict.iterkeys()``. + """ + for name in self.__names: + yield name + + def __call__(self): + """ + Iterate through the members. + + If this instance was created with ``sort=False``, the members will be + in the same order as they were passed to the constructor; otherwise the + members will be in alphabetical order by name (which is the default). + + This method is like an ordered version of ``dict.itervalues()``. + """ + for member in self.__members: + yield member + + def __contains__(self, name): + """ + Return ``True`` if namespace has a member named ``name``. + """ + return name in self.__map + + def __getitem__(self, key): + """ + Return a member by name or index, or return a slice of members. + + :param key: The name or index of a member, or a slice object. + """ + if type(key) is str: + return self.__map[key] + if type(key) in (int, slice): + return self.__members[key] + raise TypeError( + TYPE_ERROR % ('key', (str, int, slice), key, type(key)) + ) + + def __repr__(self): + """ + Return a pseudo-valid expression that could create this instance. + """ + cnt = len(self) + if cnt == 1: + m = 'member' + else: + m = 'members' + return '%s(<%d %s>, sort=%r)' % ( + self.__class__.__name__, + cnt, + m, + self.__sort, + ) + + def __todict__(self): + """ + Return a copy of the private dict mapping member name to member. + """ + return dict(self.__map) |