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Diffstat (limited to 'Doc/library/itertools.rst')
| -rw-r--r-- | Doc/library/itertools.rst | 31 |
1 files changed, 24 insertions, 7 deletions
diff --git a/Doc/library/itertools.rst b/Doc/library/itertools.rst index a0d7940..b3decae 100644 --- a/Doc/library/itertools.rst +++ b/Doc/library/itertools.rst @@ -147,10 +147,10 @@ loops that truncate the stream. >>> list(accumulate(data, max)) # running maximum [3, 4, 6, 6, 6, 9, 9, 9, 9, 9] - # Amortize a 5% loan of 1000 with 4 annual payments of 90 - >>> cashflows = [1000, -90, -90, -90, -90] - >>> list(accumulate(cashflows, lambda bal, pmt: bal*1.05 + pmt)) - [1000, 960.0, 918.0, 873.9000000000001, 827.5950000000001] + # Amortize a 5% loan of 1000 with 10 annual payments of 90 + >>> account_update = lambda bal, pmt: round(bal * 1.05) + pmt + >>> list(accumulate(repeat(-90, 10), account_update, initial=1_000)) + [1000, 960, 918, 874, 828, 779, 728, 674, 618, 559, 497] See :func:`functools.reduce` for a similar function that returns only the final accumulated value. @@ -951,7 +951,10 @@ which incur interpreter overhead. nexts = cycle(islice(nexts, num_active)) def partition(pred, iterable): - "Use a predicate to partition entries into false entries and true entries" + """Partition entries into false entries and true entries. + + If *pred* is slow, consider wrapping it with functools.lru_cache(). + """ # partition(is_odd, range(10)) --> 0 2 4 6 8 and 1 3 5 7 9 t1, t2 = tee(iterable) return filterfalse(pred, t1), filter(pred, t2) @@ -1031,7 +1034,7 @@ The following recipes have a more mathematical flavor: return chain.from_iterable(combinations(s, r) for r in range(len(s)+1)) def sieve(n): - "Primes less than n" + "Primes less than n." # sieve(30) --> 2 3 5 7 11 13 17 19 23 29 data = bytearray((0, 1)) * (n // 2) data[:3] = 0, 0, 0 @@ -1068,7 +1071,7 @@ The following recipes have a more mathematical flavor: def matmul(m1, m2): "Multiply two matrices." - # matmul([(7, 5), (3, 5)], [[2, 5], [7, 9]]) --> (49, 80), (41, 60) + # matmul([(7, 5), (3, 5)], [(2, 5), (7, 9)]) --> (49, 80), (41, 60) n = len(m2[0]) return batched(starmap(math.sumprod, product(m1, transpose(m2))), n) @@ -1109,6 +1112,17 @@ The following recipes have a more mathematical flavor: powers = map(pow, repeat(x), reversed(range(n))) return math.sumprod(coefficients, powers) + def polynomial_derivative(coefficients): + """Compute the first derivative of a polynomial. + + f(x) = x³ -4x² -17x + 60 + f'(x) = 3x² -8x -17 + """ + # polynomial_derivative([1, -4, -17, 60]) -> [3, -8, -17] + n = len(coefficients) + powers = reversed(range(1, n)) + return list(map(operator.mul, coefficients, powers)) + def nth_combination(iterable, r, index): "Equivalent to list(combinations(iterable, r))[index]" pool = tuple(iterable) @@ -1297,6 +1311,9 @@ The following recipes have a more mathematical flavor: >>> all(factored(x) == expanded(x) for x in range(-10, 11)) True + >>> polynomial_derivative([1, -4, -17, 60]) + [3, -8, -17] + >>> list(iter_index('AABCADEAF', 'A')) [0, 1, 4, 7] >>> list(iter_index('AABCADEAF', 'B')) |