cola/decorators.py

   1 import errno
   2 import functools
   3
   4
   5 __all__ = ('decorator', 'memoize', 'interruptable')
   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         @functools.wraps(caller)
  19         def _decorator(func, *dummy_args, **dummy_opts):
  20             @functools.wraps(func)
  21             def _caller(*args, **opts):
  22                 return caller(func, *args, **opts)
  23
  24             return _caller
  25
  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
  34     _decorated.func = func
  35     return _decorated
  36
  37
  38 def memoize(func):
  39     """
  40     A decorator for memoizing function calls
  41
  42     https://en.wikipedia.org/wiki/Memoization
  43
  44     """
  45     func.cache = {}
  46     return decorator(_memoize, func)
  47
  48
  49 def _memoize(func, *args, **opts):
  50     """Implements memoized cache lookups"""
  51     if opts:  # frozenset is used to ensure hashability
  52         key = (args, frozenset(list(opts.items())))
  53     else:
  54         key = args
  55     cache = func.cache  # attribute added by memoize
  56     try:
  57         result = cache[key]
  58     except KeyError:
  59         result = cache[key] = func(*args, **opts)
  60     return result
  61
  62
  63 @decorator
  64 def interruptable(func, *args, **opts):
  65     """Handle interruptible system calls
  66
  67     macOS and others are known to interrupt system calls
  68
  69         https://en.wikipedia.org/wiki/PCLSRing
  70         http://en.wikipedia.org/wiki/Unix_philosophy#Worse_is_better
  71
  72     The @interruptable decorator handles this situation
  73
  74     """
  75     while True:
  76         try:
  77             result = func(*args, **opts)
  78         except OSError as e:
  79             if e.errno in (errno.EINTR, errno.EINVAL):
  80                 continue
  81             raise e
  82         break
  83     return result