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         # pylint: disable=unused-argument
  19         @functools.wraps(caller)
  20         def _decorator(func, *dummy_args, **dummy_opts):
  21             @functools.wraps(func)
  22             def _caller(*args, **opts):
  23                 return caller(func, *args, **opts)
  24
  25             return _caller
  26
  27         _decorator.func = caller
  28         return _decorator
  29
  30     # return a decorated function
  31     @functools.wraps(func)
  32     def _decorated(*args, **opts):
  33         return caller(func, *args, **opts)
  34
  35     _decorated.func = func
  36     return _decorated
  37
  38
  39 def memoize(func):
  40     """
  41     A decorator for memoizing function calls
  42
  43     https://en.wikipedia.org/wiki/Memoization
  44
  45     """
  46     func.cache = {}
  47     return decorator(_memoize, func)
  48
  49
  50 def _memoize(func, *args, **opts):
  51     """Implements memoized cache lookups"""
  52     if opts:  # frozenset is used to ensure hashability
  53         key = (args, frozenset(list(opts.items())))
  54     else:
  55         key = args
  56     cache = func.cache  # attribute added by memoize
  57     try:
  58         result = cache[key]
  59     except KeyError:
  60         result = cache[key] = func(*args, **opts)
  61     return result
  62
  63
  64 @decorator
  65 def interruptable(func, *args, **opts):
  66     """Handle interruptible system calls
  67
  68     macOS and others are known to interrupt system calls
  69
  70         https://en.wikipedia.org/wiki/PCLSRing
  71         http://en.wikipedia.org/wiki/Unix_philosophy#Worse_is_better
  72
  73     The @interruptable decorator handles this situation
  74
  75     """
  76     while True:
  77         try:
  78             result = func(*args, **opts)
  79         except OSError as e:
  80             if e.errno in (errno.EINTR, errno.EINVAL):
  81                 continue
  82             raise e
  83         break
  84     return result