partial why three words | Python Fiddle

from functools import partial
from bisect import insort

"""
demonstrating reduce with simple functions

"""

# start with an iterable
nums = map(lambda x: x+1, range(10))

# and a binary function (with some type restraints)
add = lambda a, b: a + b
prod = lambda a, b: a * b
pair = lambda a, b: (a, b)

print reduce(add, nums, 0)
# print reduce(prod, nums, 1)
# print reduce(pair, nums, 0)

# let's try to sort
# reduce let's us think of just a single step without worrying about the recursion stuff
# insort inserts an element in sorted order, reduce lets us expand insort into a full sort

def insert_sorted(_list, elem):
    insort(_list, elem)
    return _list

# print reduce(insert_sorted, [2, 6, 8, 3, 4, 153, 8, 1], [])

"""
demonstrating partial and reduce by building a
nested dictionary accessor

"""

letters = {
     "1": {"11": {"111": "a"},
           "12": {"121": "b",
                  "122": "c"}},
     "2": {"21": {"211": "d"},
           "22": {"221": "e",
                  "222": "f"}}
          }

# print reduce(dict.__getitem__, ["1"], letters)
# print reduce(dict.__getitem__, ["2", "21", "211"], letters)

def rdce(iterable, base, func):
    """ allows reduce to take **kwargs """
    return reduce(func, iterable, base)

access = partial(rdce, func=dict.__getitem__)

# print access(["1"], letters)
# print access(["1", "12"], letters)

from_letters = partial(access, base=letters)

# print from_letters(["1", "12", "121"])
# print from_letters(["2", "22", "221"])

# for troubleshooting, there is a bug in access
# which we will discover when using from_letters

# print from_letters(["2", "22", "3"])

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