util.py

import inspect
import weakref

from pyramid.compat import (
    integer_types,
    string_types,
    text_,
    PY3,
    )

from pyramid.path import DottedNameResolver as _DottedNameResolver

class DottedNameResolver(_DottedNameResolver):
    def __init__(self, package=None): # default to package = None for bw compat
        return _DottedNameResolver.__init__(self, package)

class InstancePropertyMixin(object):
    """ Mixin that will allow an instance to add properties at
    run-time as if they had been defined via @property or @reify
    on the class itself.
    """

    def set_property(self, callable, name=None, reify=False):
        """ Add a callable or a property descriptor to the instance.

        Properties, unlike attributes, are lazily evaluated by executing
        an underlying callable when accessed. They can be useful for
        adding features to an object without any cost if those features
        go unused.

        A property may also be reified via the
        :class:`pyramid.decorator.reify` decorator by setting
        ``reify=True``, allowing the result of the evaluation to be
        cached. Thus the value of the property is only computed once for
        the lifetime of the object.

        ``callable`` can either be a callable that accepts the instance
        as
        its single positional parameter, or it can be a property
        descriptor.

        If the ``callable`` is a property descriptor, the ``name``
        parameter must be supplied or a ``ValueError`` will be raised.
        Also note that a property descriptor cannot be reified, so
        ``reify`` must be ``False``.

        If ``name`` is None, the name of the property will be computed
        from the name of the ``callable``.

        .. code-block:: python
           :linenos:

           class Foo(InstancePropertyMixin):
               _x = 1

           def _get_x(self):
               return _x

           def _set_x(self, value):
               self._x = value

           foo = Foo()
           foo.set_property(property(_get_x, _set_x), name='x')
           foo.set_property(_get_x, name='y', reify=True)

           >>> foo.x
           1
           >>> foo.y
           1
           >>> foo.x = 5
           >>> foo.x
           5
           >>> foo.y # notice y keeps the original value
           1
        """

        is_property = isinstance(callable, property)
        if is_property:
            fn = callable
            if name is None:
                raise ValueError('must specify "name" for a property')
            if reify:
                raise ValueError('cannot reify a property')
        elif name is not None:
            fn = lambda this: callable(this)
            fn.__name__ = name
            fn.__doc__ = callable.__doc__
        else:
            name = callable.__name__
            fn = callable
        if reify:
            import pyramid.decorator
            fn = pyramid.decorator.reify(fn)
        elif not is_property:
            fn = property(fn)
        attrs = { name: fn }
        parent = self.__class__
        cls = type(parent.__name__, (parent, object), attrs)
        self.__class__ = cls

class WeakOrderedSet(object):
    """ Maintain a set of items.

    Each item is stored as a weakref to avoid extending their lifetime.

    The values may be iterated over or the last item added may be
    accessed via the ``last`` property.

    If items are added more than once, the most recent addition will
    be remembered in the order:

        order = WeakOrderedSet()
        order.add('1')
        order.add('2')
        order.add('1')

        list(order) == ['2', '1']
        order.last == '1'
    """

    def __init__(self):
        self._items = {}
        self._order = []

    def add(self, item):
        """ Add an item to the set."""
        oid = id(item)
        if oid in self._items:
            self._order.remove(oid)
            self._order.append(oid)
            return
        ref = weakref.ref(item, lambda x: self.remove(item))
        self._items[oid] = ref
        self._order.append(oid)

    def remove(self, item):
        """ Remove an item from the set."""
        oid = id(item)
        if oid in self._items:
            del self._items[oid]
            self._order.remove(oid)

    def empty(self):
        """ Clear all objects from the set."""
        self._items = {}
        self._order = []

    def __len__(self):
        return len(self._order)

    def __contains__(self, item):
        oid = id(item)
        return oid in self._items

    def __iter__(self):
        return (self._items[oid]() for oid in self._order)

    @property
    def last(self):
        if self._order:
            oid = self._order[-1]
            return self._items[oid]()

def strings_differ(string1, string2):
    """Check whether two strings differ while avoiding timing attacks.

    This function returns True if the given strings differ and False
    if they are equal.  It's careful not to leak information about *where*
    they differ as a result of its running time, which can be very important
    to avoid certain timing-related crypto attacks:

        http://seb.dbzteam.org/crypto/python-oauth-timing-hmac.pdf

    """
    if len(string1) != len(string2):
        return True

    invalid_bits = 0
    for a, b in zip(string1, string2):
        invalid_bits += a != b

    return invalid_bits != 0

def object_description(object):
    """ Produce a human-consumable text description of ``object``,
    usually involving a Python dotted name. For example:

    .. code-block:: python

       >>> object_description(None)
       u'None'
       >>> from xml.dom import minidom
       >>> object_description(minidom)
       u'module xml.dom.minidom'
       >>> object_description(minidom.Attr)
       u'class xml.dom.minidom.Attr'
       >>> object_description(minidom.Attr.appendChild)
       u'method appendChild of class xml.dom.minidom.Attr'
       >>> 

    If this method cannot identify the type of the object, a generic
    description ala ``object <object.__name__>`` will be returned.

    If the object passed is already a string, it is simply returned.  If it
    is a boolean, an integer, a list, a tuple, a set, or ``None``, a
    (possibly shortened) string representation is returned.
    """
    if isinstance(object, string_types):
        return text_(object)
    if isinstance(object, integer_types):
        return text_(str(object))
    if isinstance(object, (bool, float, type(None))):
        return text_(str(object))
    if isinstance(object, set):
        if PY3: # pragma: no cover
            return shortrepr(object, '}')
        else:
            return shortrepr(object, ')')
    if isinstance(object, tuple):
        return shortrepr(object, ')')
    if isinstance(object, list):
        return shortrepr(object, ']')
    if isinstance(object, dict):
        return shortrepr(object, '}')
    module = inspect.getmodule(object)
    if module is None:
        return text_('object %s' % str(object))
    modulename = module.__name__
    if inspect.ismodule(object):
        return text_('module %s' % modulename)
    if inspect.ismethod(object):
        oself = getattr(object, '__self__', None)
        if oself is None: # pragma: no cover
            oself = getattr(object, 'im_self', None)
        return text_('method %s of class %s.%s' %
                     (object.__name__, modulename,
                      oself.__class__.__name__))

    if inspect.isclass(object):
        dottedname = '%s.%s' % (modulename, object.__name__)
        return text_('class %s' % dottedname)
    if inspect.isfunction(object):
        dottedname = '%s.%s' % (modulename, object.__name__)
        return text_('function %s' % dottedname)
    return text_('object %s' % str(object))

def shortrepr(object, closer):
    r = str(object)
    if len(r) > 100:
        r = r[:100] + ' ... %s' % closer
    return r