cola/decorators.py

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