How To 'flatten' Generators In Python?

I have a problem with 'flattening' out some generators in python. Here is my code: import itertools as it test = [[1,2,3],[4,5],[6,7,8]] def comb(possible): if len(possible) !=

Solution 1:

Here's one way to calculate a product of lists without using the built-in

def product (*iters):
  def loop (prod, first = [], *rest):
    if not rest:
      for x in first:
        yield prod + (x,)
    else:
      for x in first:
        yield from loop (prod + (x,), *rest)
  yield from loop ((), *iters)

for prod in product ("ab", "xyz"):
  print (prod)

# ('a', 'x')
# ('a', 'y')
# ('a', 'z')
# ('b', 'x')
# ('b', 'y')
# ('b', 'z')

In python, we can collect the outputs of a generator in a list by using the list constructor. Note we can also calculate the product of more than two inputs as seen below

print (list (product ("+-", "ab", "xyz")))
# [ ('+', 'a', 'x')
# , ('+', 'a', 'y')
# , ('+', 'a', 'z')
# , ('+', 'b', 'x')
# , ('+', 'b', 'y')
# , ('+', 'b', 'z')
# , ('-', 'a', 'x')
# , ('-', 'a', 'y')
# , ('-', 'a', 'z')
# , ('-', 'b', 'x')
# , ('-', 'b', 'y')
# , ('-', 'b', 'z')
# ]

Because product accepts a a list of iterables, any iterable input can be used in the product. They can even be mixed as demonstrated below

print (list (product (['@', '%'], range (2), "xy")))
# [ ('@', 0, 'x')
# , ('@', 0, 'y')
# , ('@', 1, 'x')
# , ('@', 1, 'y')
# , ('%', 0, 'x')
# , ('%', 0, 'y')
# , ('%', 1, 'x')
# , ('%', 1, 'y')
# ]

Because product is defined as a generator, we are afforded much flexibility even when writing more complex programs. Consider this program that finds right triangles made up whole numbers, a Pythagorean triple. Also note that product allows you to repeat an iterable as input as see in product (r, r, r) below

def is_triple (prod):
  (a,b,c) = prod
  return a * a + b * b == c * c

def solver (n):
  r = range (1,n)
  for p in product (r, r, r):
    if is_triple (p):
      yield p

print (list (solution in solver (20)))
# (3, 4, 5)
# (4, 3, 5)
# (5, 12, 13)
# (6, 8, 10)
# (8, 6, 10)
# (8, 15, 17)
# (9, 12, 15)
# (12, 5, 13)
# (12, 9, 15)
# (15, 8, 17)

For additional explanation and a way to see how to do this without using generators, view this answer.