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mr1azl/python-recipes.ipynb

Created May 17, 2016 10:09
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python-recipes.ipynb
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"def take(n, iterable):\n",
" \"Return first n items of the iterable as a list\"\n",
" return list(islice(iterable, n))\n",
"\n",
"def tabulate(function, start=0):\n",
" \"Return function(0), function(1), ...\"\n",
" return imap(function, count(start))\n",
"\n",
"def consume(iterator, n):\n",
" \"Advance the iterator n-steps ahead. If n is none, consume entirely.\"\n",
" # Use functions that consume iterators at C speed.\n",
" if n is None:\n",
" # feed the entire iterator into a zero-length deque\n",
" collections.deque(iterator, maxlen=0)\n",
" else:\n",
" # advance to the empty slice starting at position n\n",
" next(islice(iterator, n, n), None)\n",
"\n",
"def nth(iterable, n, default=None):\n",
" \"Returns the nth item or a default value\"\n",
" return next(islice(iterable, n, None), default)\n",
"\n",
"def all_equal(iterable):\n",
" \"Returns True if all the elements are equal to each other\"\n",
" g = groupby(iterable)\n",
" return next(g, True) and not next(g, False)\n",
"\n",
"def quantify(iterable, pred=bool):\n",
" \"Count how many times the predicate is true\"\n",
" return sum(imap(pred, iterable))\n",
"\n",
"def padnone(iterable):\n",
" \"\"\"Returns the sequence elements and then returns None indefinitely.\n",
"\n",
" Useful for emulating the behavior of the built-in map() function.\n",
" \"\"\"\n",
" return chain(iterable, repeat(None))\n",
"\n",
"def ncycles(iterable, n):\n",
" \"Returns the sequence elements n times\"\n",
" return chain.from_iterable(repeat(tuple(iterable), n))\n",
"\n",
"def dotproduct(vec1, vec2):\n",
" return sum(imap(operator.mul, vec1, vec2))\n",
"\n",
"def flatten(listOfLists):\n",
" \"Flatten one level of nesting\"\n",
" return chain.from_iterable(listOfLists)\n",
"\n",
"def repeatfunc(func, times=None, *args):\n",
" \"\"\"Repeat calls to func with specified arguments.\n",
"\n",
" Example: repeatfunc(random.random)\n",
" \"\"\"\n",
" if times is None:\n",
" return starmap(func, repeat(args))\n",
" return starmap(func, repeat(args, times))\n",
"\n",
"def pairwise(iterable):\n",
" \"s -> (s0,s1), (s1,s2), (s2, s3), ...\"\n",
" a, b = tee(iterable)\n",
" next(b, None)\n",
" return izip(a, b)\n",
"\n",
"def grouper(iterable, n, fillvalue=None):\n",
" \"Collect data into fixed-length chunks or blocks\"\n",
" # grouper('ABCDEFG', 3, 'x') --> ABC DEF Gxx\n",
" args = [iter(iterable)] * n\n",
" return izip_longest(fillvalue=fillvalue, *args)\n",
"\n",
"def roundrobin(*iterables):\n",
" \"roundrobin('ABC', 'D', 'EF') --> A D E B F C\"\n",
" # Recipe credited to George Sakkis\n",
" pending = len(iterables)\n",
" nexts = cycle(iter(it).next for it in iterables)\n",
" while pending:\n",
" try:\n",
" for next in nexts:\n",
" yield next()\n",
" except StopIteration:\n",
" pending -= 1\n",
" nexts = cycle(islice(nexts, pending))\n",
"\n",
"def powerset(iterable):\n",
" \"powerset([1,2,3]) --> () (1,) (2,) (3,) (1,2) (1,3) (2,3) (1,2,3)\"\n",
" s = list(iterable)\n",
" return chain.from_iterable(combinations(s, r) for r in range(len(s)+1))\n",
"\n",
"def unique_everseen(iterable, key=None):\n",
" \"List unique elements, preserving order. Remember all elements ever seen.\"\n",
" # unique_everseen('AAAABBBCCDAABBB') --> A B C D\n",
" # unique_everseen('ABBCcAD', str.lower) --> A B C D\n",
" seen = set()\n",
" seen_add = seen.add\n",
" if key is None:\n",
" for element in ifilterfalse(seen.__contains__, iterable):\n",
" seen_add(element)\n",
" yield element\n",
" else:\n",
" for element in iterable:\n",
" k = key(element)\n",
" if k not in seen:\n",
" seen_add(k)\n",
" yield element\n",
"\n",
"def unique_justseen(iterable, key=None):\n",
" \"List unique elements, preserving order. Remember only the element just seen.\"\n",
" # unique_justseen('AAAABBBCCDAABBB') --> A B C D A B\n",
" # unique_justseen('ABBCcAD', str.lower) --> A B C A D\n",
" return imap(next, imap(itemgetter(1), groupby(iterable, key)))\n",
"\n",
"def iter_except(func, exception, first=None):\n",
" \"\"\" Call a function repeatedly until an exception is raised.\n",
"\n",
" Converts a call-until-exception interface to an iterator interface.\n",
" Like __builtin__.iter(func, sentinel) but uses an exception instead\n",
" of a sentinel to end the loop.\n",
"\n",
" Examples:\n",
" bsddbiter = iter_except(db.next, bsddb.error, db.first)\n",
" heapiter = iter_except(functools.partial(heappop, h), IndexError)\n",
" dictiter = iter_except(d.popitem, KeyError)\n",
" dequeiter = iter_except(d.popleft, IndexError)\n",
" queueiter = iter_except(q.get_nowait, Queue.Empty)\n",
" setiter = iter_except(s.pop, KeyError)\n",
"\n",
" \"\"\"\n",
" try:\n",
" if first is not None:\n",
" yield first()\n",
" while 1:\n",
" yield func()\n",
" except exception:\n",
" pass\n",
"\n",
"def random_product(*args, **kwds):\n",
" \"Random selection from itertools.product(*args, **kwds)\"\n",
" pools = map(tuple, args) * kwds.get('repeat', 1)\n",
" return tuple(random.choice(pool) for pool in pools)\n",
"\n",
"def random_permutation(iterable, r=None):\n",
" \"Random selection from itertools.permutations(iterable, r)\"\n",
" pool = tuple(iterable)\n",
" r = len(pool) if r is None else r\n",
" return tuple(random.sample(pool, r))\n",
"\n",
"def random_combination(iterable, r):\n",
" \"Random selection from itertools.combinations(iterable, r)\"\n",
" pool = tuple(iterable)\n",
" n = len(pool)\n",
" indices = sorted(random.sample(xrange(n), r))\n",
" return tuple(pool[i] for i in indices)\n",
"\n",
"def random_combination_with_replacement(iterable, r):\n",
" \"Random selection from itertools.combinations_with_replacement(iterable, r)\"\n",
" pool = tuple(iterable)\n",
" n = len(pool)\n",
" indices = sorted(random.randrange(n) for i in xrange(r))\n",
" return tuple(pool[i] for i in indices)\n",
"\n",
"def tee_lookahead(t, i):\n",
" \"\"\"Inspect the i-th upcomping value from a tee object\n",
" while leaving the tee object at its current position.\n",
"\n",
" Raise an IndexError if the underlying iterator doesn't\n",
" have enough values.\n",
"\n",
" \"\"\"\n",
" for value in islice(t.__copy__(), i, None):\n",
" return value\n",
" raise IndexError(i)"
]
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