cpython/Lib/functools.py

"""functools.py - Tools for working with functions and callable objects
"""
# Python module wrapper for _functools C module
# to allow utilities written in Python to be added
# to the functools module.
# Written by Nick Coghlan <ncoghlan at gmail.com>
# and Raymond Hettinger <python at rcn.com>
#   Copyright (C) 2006-2010 Python Software Foundation.
# See C source code for _functools credits/copyright

__all__ = ['update_wrapper', 'wraps', 'WRAPPER_ASSIGNMENTS', 'WRAPPER_UPDATES',
           'total_ordering', 'cmp_to_key', 'lru_cache', 'reduce', 'partial']

from _functools import partial, reduce
from collections import namedtuple
try:
    from _thread import allocate_lock as Lock
except:
    from _dummy_thread import allocate_lock as Lock


################################################################################
### update_wrapper() and wraps() decorator
################################################################################

# update_wrapper() and wraps() are tools to help write
# wrapper functions that can handle naive introspection

WRAPPER_ASSIGNMENTS = ('__module__', '__name__', '__qualname__', '__doc__',
                       '__annotations__')
WRAPPER_UPDATES = ('__dict__',)
def update_wrapper(wrapper,
                   wrapped,
                   assigned = WRAPPER_ASSIGNMENTS,
                   updated = WRAPPER_UPDATES):
    """Update a wrapper function to look like the wrapped function

       wrapper is the function to be updated
       wrapped is the original function
       assigned is a tuple naming the attributes assigned directly
       from the wrapped function to the wrapper function (defaults to
       functools.WRAPPER_ASSIGNMENTS)
       updated is a tuple naming the attributes of the wrapper that
       are updated with the corresponding attribute from the wrapped
       function (defaults to functools.WRAPPER_UPDATES)
    """
    wrapper.__wrapped__ = wrapped
    for attr in assigned:
        try:
            value = getattr(wrapped, attr)
        except AttributeError:
            pass
        else:
            setattr(wrapper, attr, value)
    for attr in updated:
        getattr(wrapper, attr).update(getattr(wrapped, attr, {}))
    # Return the wrapper so this can be used as a decorator via partial()
    return wrapper

def wraps(wrapped,
          assigned = WRAPPER_ASSIGNMENTS,
          updated = WRAPPER_UPDATES):
    """Decorator factory to apply update_wrapper() to a wrapper function

       Returns a decorator that invokes update_wrapper() with the decorated
       function as the wrapper argument and the arguments to wraps() as the
       remaining arguments. Default arguments are as for update_wrapper().
       This is a convenience function to simplify applying partial() to
       update_wrapper().
    """
    return partial(update_wrapper, wrapped=wrapped,
                   assigned=assigned, updated=updated)


################################################################################
### total_ordering class decorator
################################################################################

def total_ordering(cls):
    """Class decorator that fills in missing ordering methods"""
    convert = {
        '__lt__': [('__gt__', lambda self, other: not (self < other or self == other)),
                   ('__le__', lambda self, other: self < other or self == other),
                   ('__ge__', lambda self, other: not self < other)],
        '__le__': [('__ge__', lambda self, other: not self <= other or self == other),
                   ('__lt__', lambda self, other: self <= other and not self == other),
                   ('__gt__', lambda self, other: not self <= other)],
        '__gt__': [('__lt__', lambda self, other: not (self > other or self == other)),
                   ('__ge__', lambda self, other: self > other or self == other),
                   ('__le__', lambda self, other: not self > other)],
        '__ge__': [('__le__', lambda self, other: (not self >= other) or self == other),
                   ('__gt__', lambda self, other: self >= other and not self == other),
                   ('__lt__', lambda self, other: not self >= other)]
    }
    # Find user-defined comparisons (not those inherited from object).
    roots = [op for op in convert if getattr(cls, op, None) is not getattr(object, op, None)]
    if not roots:
        raise ValueError('must define at least one ordering operation: < > <= >=')
    root = max(roots)       # prefer __lt__ to __le__ to __gt__ to __ge__
    for opname, opfunc in convert[root]:
        if opname not in roots:
            opfunc.__name__ = opname
            opfunc.__doc__ = getattr(int, opname).__doc__
            setattr(cls, opname, opfunc)
    return cls


################################################################################
### cmp_to_key() function converter
################################################################################

def cmp_to_key(mycmp):
    """Convert a cmp= function into a key= function"""
    class K(object):
        __slots__ = ['obj']
        def __init__(self, obj):
            self.obj = obj
        def __lt__(self, other):
            return mycmp(self.obj, other.obj) < 0
        def __gt__(self, other):
            return mycmp(self.obj, other.obj) > 0
        def __eq__(self, other):
            return mycmp(self.obj, other.obj) == 0
        def __le__(self, other):
            return mycmp(self.obj, other.obj) <= 0
        def __ge__(self, other):
            return mycmp(self.obj, other.obj) >= 0
        def __ne__(self, other):
            return mycmp(self.obj, other.obj) != 0
        __hash__ = None
    return K

try:
    from _functools import cmp_to_key
except ImportError:
    pass


################################################################################
### LRU Cache function decorator
################################################################################

_CacheInfo = namedtuple("CacheInfo", ["hits", "misses", "maxsize", "currsize"])

def lru_cache(maxsize=100, typed=False):
    """Least-recently-used cache decorator.

    If *maxsize* is set to None, the LRU features are disabled and the cache
    can grow without bound.

    If *typed* is True, arguments of different types will be cached separately.
    For example, f(3.0) and f(3) will be treated as distinct calls with
    distinct results.

    Arguments to the cached function must be hashable.

    View the cache statistics named tuple (hits, misses, maxsize, currsize) with
    f.cache_info().  Clear the cache and statistics with f.cache_clear().
    Access the underlying function with f.__wrapped__.

    See:  http://en.wikipedia.org/wiki/Cache_algorithms#Least_Recently_Used

    """
    # Users should only access the lru_cache through its public API:
    #       cache_info, cache_clear, and f.__wrapped__
    # The internals of the lru_cache are encapsulated for thread safety and
    # to allow the implementation to change (including a possible C version).

    def decorating_function(user_function):

        cache = dict()
        hits = misses = 0
        kwd_mark = (object(),)          # separate positional and keyword args
        cache_get = cache.get           # bound method to lookup key or return None
        _len = len                      # localize the global len() function
        lock = Lock()                   # because linkedlist updates aren't threadsafe
        root = []                       # root of the circular doubly linked list
        root[:] = [root, root, None, None]      # initialize by pointing to self
        PREV, NEXT, KEY, RESULT = 0, 1, 2, 3    # names for the link fields

        def make_key(args, kwds, typed, tuple=tuple, sorted=sorted, type=type):
            # helper function to build a cache key from positional and keyword args
            key = args
            if kwds:
                sorted_items = tuple(sorted(kwds.items()))
                key += kwd_mark + sorted_items
            if typed:
                key += tuple(type(v) for v in args)
                if kwds:
                    key += tuple(type(v) for k, v in sorted_items)
            return key

        if maxsize == 0:

            @wraps(user_function)
            def wrapper(*args, **kwds):
                # no caching, just do a statistics update after a successful call
                nonlocal misses
                result = user_function(*args, **kwds)
                misses += 1
                return result

        elif maxsize is None:

            @wraps(user_function)
            def wrapper(*args, **kwds):
                # simple caching without ordering or size limit
                nonlocal hits, misses
                key = make_key(args, kwds, typed) if kwds or typed else args
                result = cache_get(key, root)   # root used here as a unique not-found sentinel
                if result is not root:
                    hits += 1
                    return result
                result = user_function(*args, **kwds)
                cache[key] = result
                misses += 1
                return result

        else:

            @wraps(user_function)
            def wrapper(*args, **kwds):
                # size limited caching that tracks accesses by recency
                nonlocal hits, misses
                key = make_key(args, kwds, typed) if kwds or typed else args
                with lock:
                    link = cache_get(key)
                    if link is not None:
                        # record recent use of the key by moving it to the front of the list
                        link_prev, link_next, key, result = link
                        link_prev[NEXT] = link_next
                        link_next[PREV] = link_prev
                        last = root[PREV]
                        last[NEXT] = root[PREV] = link
                        link[PREV] = last
                        link[NEXT] = root
                        hits += 1
                        return result
                result = user_function(*args, **kwds)
                with lock:
                    last = root[PREV]
                    link = [last, root, key, result]
                    cache[key] = last[NEXT] = root[PREV] = link
                    if _len(cache) > maxsize:
                        # purge least recently used cache entry
                        old_prev, old_next, old_key, old_result = root[NEXT]
                        root[NEXT] = old_next
                        old_next[PREV] = root
                        del cache[old_key]
                    misses += 1
                return result

        def cache_info():
            """Report cache statistics"""
            with lock:
                return _CacheInfo(hits, misses, maxsize, len(cache))

        def cache_clear():
            """Clear the cache and cache statistics"""
            nonlocal hits, misses
            with lock:
                cache.clear()
                root[:] = [root, root, None, None]
                hits = misses = 0

        wrapper.cache_info = cache_info
        wrapper.cache_clear = cache_clear
        return wrapper

    return decorating_function