It seems that accumulate keeps the previous results, whereas reduce (which is known as fold in other languages) does not necessarily. e.g. list(accumulate([1,2,3], operator.add)) would return [1,3,6] whereas a plain fold would return 6 Also (just for fun, don’t do this) you can define accumulate in terms of reduce def accumulate(xs, f): return reduce(lambda a, … Read more
To implement Kevin’s answer for an arbitrary number of source iterables, combining reduce and mul: >>> import functools, itertools, operator >>> iters = [[1, 2, 3], [4, 5, 6], [7, 8, 9]] >>> functools.reduce(operator.mul, map(len, iters), 1) 27 >>> len(list(itertools.product(*iters))) 27 Note that this will not work if your source iterables are themselves iterators, rather … Read more
itertools.groupby collects together contiguous items with the same key. If you want all items with the same key, you have to sort self.data first. for mid, group in itertools.groupby( sorted(self.data,key=operator.itemgetter(1)), key=operator.itemgetter(1)):
The primary purpose of itertools.repeat is to supply a stream of constant values to be used with map or zip: >>> list(map(pow, range(10), repeat(2))) # list of squares [0, 1, 4, 9, 16, 25, 36, 49, 64, 81] The secondary purpose is that it gives a very fast way to loop a fixed number of … Read more
itertools.permutations() simply works this way. It takes an arbitrary iterable as an argument, and always returns an iterator yielding tuples. It doesn’t (and shouldn’t) special-case strings. To get a list of strings, you can always join the tuples yourself: list(map(“”.join, itertools.permutations(‘1234’)))
itertools.ifilter() was removed in Python 3 because the built-in filter() function provides the same functionality now. If you need to write code that can run in both Python 2 and Python 3, use imports from the future_builtins module (only in Python 2, so use a try…except ImportError: guard): try: # Python 2 from future_builtins import … Read more
itertools.imap() is in Python 2, but not in Python 3. Actually, that function was moved to just the map function in Python 3 and if you want to use the old Python 2 map, you must use list(map()).
The simplest way is to use itertools.product: a = [“foo”, “melon”] b = [True, False] c = list(itertools.product(a, b)) >> [(“foo”, True), (“foo”, False), (“melon”, True), (“melon”, False)]
An optional boolean keyword argument, strict, is introduced for the built-in zip function in PEP 618. Quoting What’s New In Python 3.10: The zip() function now has an optional strict flag, used to require that all the iterables have an equal length. When enabled, a ValueError is raised if one of the arguments is exhausted … Read more
iter.next() was removed in python 3. Use next(iter) instead. So in your example change itertools.cycle().next() to next(itertools.cycle()) There is a good example here along with various other porting to python 3 tips. It also compares various other next() idioms in python 2.x vs python 3.x