class symbol(object):
"""A constant symbol.
>>> symbol('foo') is symbol('foo')
True
>>> symbol('foo')
<symbol 'foo>
A slight refinement of the MAGICCOOKIE=object() pattern. The primary
advantage of symbol() is its repr(). They are also singletons.
Repeated calls of symbol('name') will all return the same instance.
The optional ``doc`` argument assigns to ``__doc__``. This
is strictly so that Sphinx autoattr picks up the docstring we want
(it doesn't appear to pick up the in-module docstring if the datamember
is in a different module - autoattribute also blows up completely).
If Sphinx fixes/improves this then we would no longer need
``doc`` here.
"""
symbols = {}
_lock = threading.Lock()
def __new__(cls, name, doc=None):
cls._lock.acquire()
try:
sym = cls.symbols.get(name)
if sym is None:
cls.symbols[name] = sym = _symbol(name, doc)
return sym
finally:
symbol._lock.release()
def counter():
"""Return a threadsafe counter function."""
lock = threading.Lock()
counter = itertools.count(1L)
# avoid the 2to3 "next" transformation...
def _next():
lock.acquire()
try:
return counter.next()
finally:
lock.release()
return _next