cola/decorators.py

   1 from __future__ import absolute_import, division, print_function, 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
  26             return _caller
  27
  28         _decorator.func = caller
  29         return _decorator
  30
  31     # return a decorated function
  32     @functools.wraps(func)
  33     def _decorated(*args, **opts):
  34         return caller(func, *args, **opts)
  35
  36     _decorated.func = func
  37     return _decorated
  38
  39
  40 def memoize(func):
  41     """
  42     A decorator for memoizing function calls
  43
  44     http://en.wikipedia.org/wiki/Memoization
  45
  46     """
  47     func.cache = {}
  48     return decorator(_memoize, func)
  49
  50
  51 def _memoize(func, *args, **opts):
  52     """Implements memoized cache lookups"""
  53     if opts:  # frozenset is used to ensure hashability
  54         key = (args, frozenset(list(opts.items())))
  55     else:
  56         key = args
  57     cache = func.cache  # attribute added by memoize
  58     try:
  59         result = cache[key]
  60     except KeyError:
  61         result = cache[key] = func(*args, **opts)
  62     return result
  63
  64
  65 @decorator
  66 def interruptable(func, *args, **opts):
  67     """Handle interruptible system calls
  68
  69     OSX and others are known to interrupt system calls
  70
  71         http://en.wikipedia.org/wiki/PCLSRing
  72         http://en.wikipedia.org/wiki/Unix_philosophy#Worse_is_better
  73
  74     The @interruptable decorator handles this situation
  75
  76     """
  77     while True:
  78         try:
  79             result = func(*args, **opts)
  80         except (IOError, OSError) as e:
  81             if e.errno in (errno.EINTR, errno.EINVAL):
  82                 continue
  83             raise e
  84         else:
  85             break
  86     return result