193 lines
7.6 KiB
Python
193 lines
7.6 KiB
Python
"""functools.py - Tools for working with functions and callable objects
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"""
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# Python module wrapper for _functools C module
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# to allow utilities written in Python to be added
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# to the functools module.
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# Written by Nick Coghlan <ncoghlan at gmail.com>
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# and Raymond Hettinger <python at rcn.com>
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# Copyright (C) 2006-2010 Python Software Foundation.
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# See C source code for _functools credits/copyright
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__all__ = ['update_wrapper', 'wraps', 'WRAPPER_ASSIGNMENTS', 'WRAPPER_UPDATES',
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'total_ordering', 'cmp_to_key', 'lfu_cache', 'lru_cache']
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from _functools import partial, reduce
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from collections import OrderedDict, Counter
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from heapq import nsmallest
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from operator import itemgetter
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# update_wrapper() and wraps() are tools to help write
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# wrapper functions that can handle naive introspection
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WRAPPER_ASSIGNMENTS = ('__module__', '__name__', '__doc__', '__annotations__')
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WRAPPER_UPDATES = ('__dict__',)
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def update_wrapper(wrapper,
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wrapped,
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assigned = WRAPPER_ASSIGNMENTS,
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updated = WRAPPER_UPDATES):
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"""Update a wrapper function to look like the wrapped function
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wrapper is the function to be updated
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wrapped is the original function
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assigned is a tuple naming the attributes assigned directly
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from the wrapped function to the wrapper function (defaults to
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functools.WRAPPER_ASSIGNMENTS)
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updated is a tuple naming the attributes of the wrapper that
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are updated with the corresponding attribute from the wrapped
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function (defaults to functools.WRAPPER_UPDATES)
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"""
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for attr in assigned:
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if hasattr(wrapped, attr):
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setattr(wrapper, attr, getattr(wrapped, attr))
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for attr in updated:
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getattr(wrapper, attr).update(getattr(wrapped, attr, {}))
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# Return the wrapper so this can be used as a decorator via partial()
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return wrapper
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def wraps(wrapped,
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assigned = WRAPPER_ASSIGNMENTS,
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updated = WRAPPER_UPDATES):
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"""Decorator factory to apply update_wrapper() to a wrapper function
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Returns a decorator that invokes update_wrapper() with the decorated
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function as the wrapper argument and the arguments to wraps() as the
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remaining arguments. Default arguments are as for update_wrapper().
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This is a convenience function to simplify applying partial() to
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update_wrapper().
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"""
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return partial(update_wrapper, wrapped=wrapped,
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assigned=assigned, updated=updated)
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def total_ordering(cls):
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"""Class decorator that fills in missing ordering methods"""
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convert = {
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'__lt__': [('__gt__', lambda self, other: other < self),
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('__le__', lambda self, other: not other < self),
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('__ge__', lambda self, other: not self < other)],
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'__le__': [('__ge__', lambda self, other: other <= self),
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('__lt__', lambda self, other: not other <= self),
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('__gt__', lambda self, other: not self <= other)],
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'__gt__': [('__lt__', lambda self, other: other > self),
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('__ge__', lambda self, other: not other > self),
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('__le__', lambda self, other: not self > other)],
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'__ge__': [('__le__', lambda self, other: other >= self),
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('__gt__', lambda self, other: not other >= self),
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('__lt__', lambda self, other: not self >= other)]
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}
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roots = set(dir(cls)) & set(convert)
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if not roots:
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raise ValueError('must define at least one ordering operation: < > <= >=')
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root = max(roots) # prefer __lt__ to __le__ to __gt__ to __ge__
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for opname, opfunc in convert[root]:
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if opname not in roots:
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opfunc.__name__ = opname
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opfunc.__doc__ = getattr(int, opname).__doc__
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setattr(cls, opname, opfunc)
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return cls
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def cmp_to_key(mycmp):
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"""Convert a cmp= function into a key= function"""
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class K(object):
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def __init__(self, obj, *args):
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self.obj = obj
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def __lt__(self, other):
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return mycmp(self.obj, other.obj) < 0
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def __gt__(self, other):
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return mycmp(self.obj, other.obj) > 0
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def __eq__(self, other):
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return mycmp(self.obj, other.obj) == 0
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def __le__(self, other):
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return mycmp(self.obj, other.obj) <= 0
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def __ge__(self, other):
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return mycmp(self.obj, other.obj) >= 0
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def __ne__(self, other):
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return mycmp(self.obj, other.obj) != 0
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def __hash__(self):
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raise TypeError('hash not implemented')
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return K
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def lfu_cache(maxsize=100):
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'''Least-frequently-used cache decorator.
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Arguments to the cached function must be hashable.
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Cache performance statistics stored in f.hits and f.misses.
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Clear the cache using f.clear().
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http://en.wikipedia.org/wiki/Cache_algorithms#Least-Frequently_Used
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'''
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def decorating_function(user_function):
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cache = {} # mapping of args to results
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use_count = Counter() # times each key has been accessed
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kwd_mark = object() # separate positional and keyword args
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@wraps(user_function)
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def wrapper(*args, **kwds):
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key = args
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if kwds:
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key += (kwd_mark,) + tuple(sorted(kwds.items()))
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use_count[key] += 1 # count a use of this key
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try:
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result = cache[key]
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wrapper.hits += 1
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except KeyError:
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result = user_function(*args, **kwds)
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cache[key] = result
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wrapper.misses += 1
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if len(cache) > maxsize:
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# purge the 10% least frequently used entries
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for key, _ in nsmallest(maxsize // 10,
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use_count.items(),
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key=itemgetter(1)):
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del cache[key], use_count[key]
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return result
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def clear():
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'Clear the cache and cache statistics'
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cache.clear()
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use_count.clear()
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wrapper.hits = wrapper.misses = 0
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wrapper.hits = wrapper.misses = 0
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wrapper.clear = clear
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return wrapper
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return decorating_function
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def lru_cache(maxsize=100):
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'''Least-recently-used cache decorator.
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Arguments to the cached function must be hashable.
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Cache performance statistics stored in f.hits and f.misses.
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Clear the cache using f.clear().
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http://en.wikipedia.org/wiki/Cache_algorithms#Least_Recently_Used
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'''
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def decorating_function(user_function):
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cache = OrderedDict() # ordered least recent to most recent
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kwd_mark = object() # separate positional and keyword args
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@wraps(user_function)
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def wrapper(*args, **kwds):
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key = args
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if kwds:
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key += (kwd_mark,) + tuple(sorted(kwds.items()))
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try:
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result = cache.pop(key)
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wrapper.hits += 1
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except KeyError:
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result = user_function(*args, **kwds)
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wrapper.misses += 1
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if len(cache) >= maxsize:
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cache.popitem(0) # purge least recently used cache entry
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cache[key] = result # record recent use of this key
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return result
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def clear():
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'Clear the cache and cache statistics'
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cache.clear()
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wrapper.hits = wrapper.misses = 0
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wrapper.hits = wrapper.misses = 0
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wrapper.clear = clear
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return wrapper
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return decorating_function
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