cola/decorators.py

   1 from __future__ import division, absolute_import, unicode_literals
   2 import errno
   3 import functools
   4
   5
   6 __all__ = ('decorator', 'memoize', 'interruptable')
   7
   8
   9 def decorator(caller, func=None):
  10     """
  11     Create a new decorator
  12
  13     decorator(caller) converts a caller function into a decorator;
  14     decorator(caller, func) decorates a function using a caller.
  15
  16     """
  17     if func is None:
  18         # return a decorator
  19         # pylint: disable=unused-argument
  20         @functools.wraps(caller)
  21         def _decorator(f, *dummy_args, **dummy_opts):
  22             @functools.wraps(f)
  23             def _caller(*args, **opts):
  24                 return caller(f, *args, **opts)
  25             return _caller
  26         _decorator.func = caller
  27         return _decorator
  28
  29     # return a decorated function
  30     @functools.wraps(func)
  31     def _decorated(*args, **opts):
  32         return caller(func, *args, **opts)
  33     _decorated.func = func
  34     return _decorated
  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(list(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, OSError) as e:
  78             if e.errno in (errno.EINTR, errno.EINVAL):
  79                 continue
  80             raise e
  81         else:
  82             break
  83     return result