cola/decorators.py

   1 __all__ = ('decorated', 'deprecator', 'memoize', 'interruptable')
   2
   3 import errno
   4
   5
   6 def decorator(caller, func=None):
   7     """
   8     Create a new decorator
   9
  10     decorator(caller) converts a caller function into a decorator;
  11     decorator(caller, func) decorates a function using a caller.
  12
  13     """
  14     if func is None:
  15         # return a decorator
  16         def _decorator(f, *args, **opts):
  17             def _caller(*args, **opts):
  18                 return caller(f, *args, **opts)
  19             return _caller
  20         return _decorator
  21     else:
  22         # return a decorated function
  23         def _decorated(*args, **opts):
  24             return caller(func, *args, **opts)
  25         return _decorated
  26
  27
  28 @decorator
  29 def deprecated(func, *args, **kw):
  30     "A decorator for deprecated functions"
  31     import warnings
  32     warnings.warn('Calling deprecated function %r' % func.__name__,
  33                   DeprecationWarning, stacklevel=3)
  34     return func(*args, **kw)
  35
  36
  37 def memoize(func):
  38     """
  39     A decorator for memoizing function calls
  40
  41     http://en.wikipedia.org/wiki/Memoization
  42
  43     """
  44     func.cache = {}
  45     return decorator(_memoize, func)
  46
  47
  48 def _memoize(func, *args, **opts):
  49     """Implements memoized cache lookups"""
  50     if opts: # frozenset is used to ensure hashability
  51         key = args, frozenset(opts.items())
  52     else:
  53         key = args
  54     cache = func.cache # attribute added by memoize
  55     try:
  56         result = cache[key]
  57     except KeyError:
  58         result = cache[key] = func(*args, **opts)
  59     return result
  60
  61
  62 @decorator
  63 def interruptable(func, *args, **opts):
  64     """Handle interruptable system calls
  65
  66     OSX and others are known to interrupt system calls
  67
  68         http://en.wikipedia.org/wiki/PCLSRing
  69         http://en.wikipedia.org/wiki/Unix_philosophy#Worse_is_better
  70
  71     The @interruptable decorator handles this situation
  72
  73     """
  74     while True:
  75         try:
  76             result = func(*args, **opts)
  77         except IOError, e:
  78             if e.errno == errno.EINTR:
  79                 continue
  80             raise e
  81         except OSError, e:
  82             if e.errno == errno.EINTR:
  83                 continue
  84             raise e
  85         else:
  86             break
  87     return result