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