cola/decorators.py

   1 __all__ = ('decorator', 'deprecated', 'memoize')
   2
   3
   4 def decorator(caller, func=None):
   5     """
   6     decorator(caller) converts a caller function into a decorator;
   7     decorator(caller, func) decorates a function using a caller.
   8     """
   9     if func is None: # returns a decorator
  10         def _decorator(f, *args, **opts):
  11             def _caller(*args, **opts):
  12                 return caller(f, *args, **opts)
  13             return _caller
  14         return _decorator
  15
  16     else: # returns a decorated function
  17         def _decorator(*args, **opts):
  18             return caller(func, *args, **opts)
  19         return _decorator
  20
  21
  22 @decorator
  23 def deprecated(func, *args, **kw):
  24     "A decorator for deprecated functions"
  25     import warnings
  26     warnings.warn('Calling deprecated function %r' % func.__name__,
  27                   DeprecationWarning, stacklevel=3)
  28     return func(*args, **kw)
  29
  30
  31 def memoize(func):
  32     """
  33     A decorator for memoizing function calls
  34
  35     http://en.wikipedia.org/wiki/Memoization
  36
  37     """
  38     func.cache = {}
  39     return decorator(_memoize, func)
  40
  41
  42 def _memoize(func, *args, **opts):
  43     """Implements memoized cache lookups"""
  44     if opts: # frozenset is used to ensure hashability
  45         key = args, frozenset(opts.items())
  46     else:
  47         key = args
  48     cache = func.cache # attribute added by memoize
  49     try:
  50         return cache[key]
  51     except KeyError:
  52         cache[key] = result = func(*args, **opts)
  53         return result