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# Copyright (c) 2013, Mahmoud Hashemi
#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions are
# met:
#
# * Redistributions of source code must retain the above copyright
# notice, this list of conditions and the following disclaimer.
#
# * Redistributions in binary form must reproduce the above
# copyright notice, this list of conditions and the following
# disclaimer in the documentation and/or other materials provided
# with the distribution.
#
# * The names of the contributors may not be used to endorse or
# promote products derived from this software without specific
# prior written permission.
#
# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
# OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
"""Python's built-in :mod:`functools` module builds several useful
utilities on top of Python's first-class function support.
``typeutils`` attempts to do the same for metaprogramming with types
and instances.
"""
import sys
from collections import deque
_issubclass = issubclass
def make_sentinel(name='_MISSING', var_name=None):
"""Creates and returns a new **instance** of a new class, suitable for
usage as a "sentinel", a kind of singleton often used to indicate
a value is missing when ``None`` is a valid input.
Args:
name (str): Name of the Sentinel
var_name (str): Set this name to the name of the variable in
its respective module enable pickleability. Note:
pickleable sentinels should be global constants at the top
level of their module.
>>> make_sentinel(var_name='_MISSING')
_MISSING
The most common use cases here in boltons are as default values
for optional function arguments, partly because of its
less-confusing appearance in automatically generated
documentation. Sentinels also function well as placeholders in queues
and linked lists.
.. note::
By design, additional calls to ``make_sentinel`` with the same
values will not produce equivalent objects.
>>> make_sentinel('TEST') == make_sentinel('TEST')
False
>>> type(make_sentinel('TEST')) == type(make_sentinel('TEST'))
False
"""
class Sentinel:
def __init__(self):
self.name = name
self.var_name = var_name
def __repr__(self):
if self.var_name:
return self.var_name
return f'{self.__class__.__name__}({self.name!r})'
if var_name:
def __reduce__(self):
return self.var_name
def __bool__(self):
return False
def __copy__(self):
return self
def __deepcopy__(self, _memo):
return self
if var_name:
frame = sys._getframe(1)
module = frame.f_globals.get('__name__')
if not module or module not in sys.modules:
raise ValueError('Pickleable sentinel objects (with var_name) can only'
' be created from top-level module scopes')
Sentinel.__module__ = module
return Sentinel()
def issubclass(subclass, baseclass):
"""Just like the built-in :func:`issubclass`, this function checks
whether *subclass* is inherited from *baseclass*. Unlike the
built-in function, this ``issubclass`` will simply return
``False`` if either argument is not suitable (e.g., if *subclass*
is not an instance of :class:`type`), instead of raising
:exc:`TypeError`.
Args:
subclass (type): The target class to check.
baseclass (type): The base class *subclass* will be checked against.
>>> class MyObject(object): pass
...
>>> issubclass(MyObject, object) # always a fun fact
True
>>> issubclass('hi', 'friend')
False
"""
try:
return _issubclass(subclass, baseclass)
except TypeError:
return False
def get_all_subclasses(cls):
"""Recursively finds and returns a :class:`list` of all types
inherited from *cls*.
>>> class A(object):
... pass
...
>>> class B(A):
... pass
...
>>> class C(B):
... pass
...
>>> class D(A):
... pass
...
>>> [t.__name__ for t in get_all_subclasses(A)]
['B', 'D', 'C']
>>> [t.__name__ for t in get_all_subclasses(B)]
['C']
"""
try:
to_check = deque(cls.__subclasses__())
except (AttributeError, TypeError):
raise TypeError('expected type object, not %r' % cls)
seen, ret = set(), []
while to_check:
cur = to_check.popleft()
if cur in seen:
continue
ret.append(cur)
seen.add(cur)
to_check.extend(cur.__subclasses__())
return ret
class classproperty:
"""Much like a :class:`property`, but the wrapped get function is a
class method. For simplicity, only read-only properties are
implemented.
"""
def __init__(self, fn):
self.fn = fn
def __get__(self, instance, cls):
return self.fn(cls)
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