cola/decorators.py

   1 __all__ = ('decorator', '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 def memoize(func):
  29     """
  30     A decorator for memoizing function calls
  31
  32     http://en.wikipedia.org/wiki/Memoization
  33
  34     """
  35     func.cache = {}
  36     return decorator(_memoize, func)
  37
  38
  39 def _memoize(func, *args, **opts):
  40     """Implements memoized cache lookups"""
  41     if opts: # frozenset is used to ensure hashability
  42         key = args, frozenset(opts.items())
  43     else:
  44         key = args
  45     cache = func.cache # attribute added by memoize
  46     try:
  47         result = cache[key]
  48     except KeyError:
  49         result = cache[key] = func(*args, **opts)
  50     return result
  51
  52
  53 @decorator
  54 def interruptable(func, *args, **opts):
  55     """Handle interruptable system calls
  56
  57     OSX and others are known to interrupt system calls
  58
  59         http://en.wikipedia.org/wiki/PCLSRing
  60         http://en.wikipedia.org/wiki/Unix_philosophy#Worse_is_better
  61
  62     The @interruptable decorator handles this situation
  63
  64     """
  65     while True:
  66         try:
  67             result = func(*args, **opts)
  68         except IOError, e:
  69             if e.errno == errno.EINTR:
  70                 continue
  71             raise e
  72         except OSError, e:
  73             if e.errno in (errno.EINTR, errno.EINVAL):
  74                 continue
  75             raise e
  76         else:
  77             break
  78     return result