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Foundational classes and functions.
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Base class for classes that can be locked into a read-only state.
Be forewarned that Python does not offer true read-only attributes for
user-defined classes. Do *not* rely upon the read-only-ness of this
class for security purposes!
The point of this class is not to make it impossible to set or to delete
attributes after an instance is locked, but to make it impossible to do so
*accidentally*. Rather than constantly reminding our programmers of things
like, for example, "Don't set any attributes on this ``FooBar`` instance
because doing so wont be thread-safe", this class offers a real way to
enforce read-only attribute usage.
For example, before a `ReadOnly` instance is locked, you can set and delete
its attributes as normal:
>>> class Person(ReadOnly):
... pass
...
>>> p = Person()
>>> p.name = 'John Doe'
>>> p.phone = '123-456-7890'
>>> del p.phone
But after an instance is locked, you cannot set its attributes:
>>> p.__islocked__() # Is this instance locked?
False
>>> p.__lock__() # This will lock the instance
>>> p.__islocked__()
True
>>> p.department = 'Engineering'
Traceback (most recent call last):
...
AttributeError: locked: cannot set Person.department to 'Engineering'
Nor can you deleted its attributes:
>>> del p.name
Traceback (most recent call last):
...
AttributeError: locked: cannot delete Person.name
However, as noted at the start, there are still obscure ways in which
attributes can be set or deleted on a locked `ReadOnly` instance. For
example:
>>> object.__setattr__(p, 'department', 'Engineering')
>>> p.department
'Engineering'
>>> object.__delattr__(p, 'name')
>>> hasattr(p, 'name')
False
But again, the point is that a programmer would never employ the above
techniques *accidentally*.
Lastly, this example aside, you should use the `lock()` function rather
than the `ReadOnly.__lock__()` method. And likewise, you should
use the `islocked()` function rather than the `ReadOnly.__islocked__()`
method. For example:
>>> readonly = ReadOnly()
>>> islocked(readonly)
False
>>> lock(readonly) is readonly # lock() returns the instance
True
>>> islocked(readonly)
True
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Put this instance into a read-only state.
After the instance has been locked, attempting to set or delete an
attribute will raise an AttributeError.
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Return True if instance is locked, otherwise False.
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If unlocked, set attribute named ``name`` to ``value``.
If this instance is locked, an AttributeError will be raised.
:param name: Name of attribute to set.
:param value: Value to assign to attribute.
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If unlocked, delete attribute named ``name``.
If this instance is locked, an AttributeError will be raised.
:param name: Name of attribute to delete.
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Lock an instance of the `ReadOnly` class or similar.
This function can be used to lock instances of any class that implements
the same locking API as the `ReadOnly` class. For example, this function
can lock instances of the `config.Env` class.
So that this function can be easily used within an assignment, ``instance``
is returned after it is locked. For example:
>>> readonly = ReadOnly()
>>> readonly is lock(readonly)
True
>>> readonly.attr = 'This wont work'
Traceback (most recent call last):
...
AttributeError: locked: cannot set ReadOnly.attr to 'This wont work'
Also see the `islocked()` function.
:param instance: The instance of `ReadOnly` (or similar) to lock.
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Return ``True`` if ``instance`` is locked.
This function can be used on an instance of the `ReadOnly` class or an
instance of any other class implemented the same locking API.
For example:
>>> readonly = ReadOnly()
>>> islocked(readonly)
False
>>> readonly.__lock__()
>>> islocked(readonly)
True
Also see the `lock()` function.
:param instance: The instance of `ReadOnly` (or similar) to interrogate.
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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:
>>> check_name('MyName')
Traceback (most recent call last):
...
ValueError: name must match '^[a-z][_a-z0-9]*[a-z0-9]$|^[a-z]$'; got 'MyName'
Also, this function will raise a ``TypeError`` if ``name`` is not an
``str`` instance. For example:
>>> check_name(u'my_name')
Traceback (most recent call last):
...
TypeError: name: need a ; got u'my_name' (a )
So that `check_name()` can be easily used within an assignment, ``name``
is returned unchanged if it passes the check. For example:
>>> n = check_name('my_name')
>>> n
'my_name'
:param name: Identifier to test.
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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)
We can then access ``my_member`` both as an attribute and as a dictionary
item:
>>> 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*
(as opposed to the member names). Think of it 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, simpler way to do it
[Member(0), Member(1), Member(2)]
Another convenience method is `NameSpace.__todict__()`, which will return
a copy of the ``dict`` mapping the member names to the members.
For example:
>>> ns.__todict__()
{'member1': Member(1), 'member0': Member(0), 'member2': Member(2)}
As `NameSpace.__init__()` locks the instance, `NameSpace` instances are
read-only from the get-go. An ``AttributeError`` is raised if you try to
set *any* attribute on a `NameSpace` instance. 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.
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Return the number of members.
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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()``.
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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()``.
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Return ``True`` if namespace has a member named ``name``.
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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.
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Return a pseudo-valid expression that could create this instance.
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Return a copy of the private dict mapping member name to member.
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