On 21/04/2012 09:36, Steven D'Aprano wrote:
[...]
Here is how I would write the above.
import functools
def memoise(func):
"""Decorator to memoise a function."""
cache = {}
@functools.wraps(func)
def inner(*args, **kwargs):
# Make sure keyword args are always looked up in a consistent
# order by sorting. One minor subtlety: since kwargs cannot
# have duplicate keys, sorted() will never try to break ties
# by comparing values. So this will work even for unsortable
# values like complex numbers.
kw = tuple(sorted(kwargs.items()))
try:
# Cache hit?
result = cache[(args, kw)]
except KeyError:
# Cache miss.
result = func(*args, **kwargs)
cache[(args, kw)] = result
except TypeError:
# Cache failure; at least one argument is uncacheable.
result = func(*args, **kwargs)
# Is the cache too big?
if len(cache)> 1000:
# Dump an arbitrary item. A LRU (least recently used) cache
# would be better, but this will do.
cache.popitem()
return result
# Expose the cache to the outside world.
inner._cache = cache
return inner
Thanks. Incidentally, would there be any way to look at the value of
cache if it weren't for the statement inner._cache = cache? For that
matter, I don't understand why 'cache' isn't in inner.__globals__.
[...]
But I don't know how. I know that I can see the default arguments of the
original function using func.__defaults__, but without knowing the
number and names of func's positional arguments (which I don't know how
to find out) this doesn't help me. Any suggestions?
http://docs.python.org/release/3.1.5/library/inspect.html?#inspect.getfullargspec
def f(a, b=1, *args, c, d=2, **kwargs):
... x = 42
... return (a,b,c,d,args,kwargs)
...
import inspect
inspect.getfullargspec(f)
FullArgSpec(args=['a', 'b'], varargs='args', varkw='kwargs',
defaults=(1,), kwonlyargs=['c', 'd'], kwonlydefaults={'d': 2},
annotations={})
Cool; that's not available for Python 2 but it looks like
inspect.getargspec() is and does pretty much the same thing. Also
inspect.getcallargs() does exactly what I need for my decorator. Thanks
very much for your help.
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