Python appending each integer in list to each integer in another list

Question

Noob here, Okay so i want to append each integer generated from "range(3,20)" to another similar range "range(22,40)

from itertools import chain

L1 = 3
H1 = 20
L2 = 22
H2 = 40

new_list = [x for x in chain(range(L1,H1))]
new_list2 = [xx for xx in chain(range(L2,H2))]
print (new_list + new_list2)

Results should be:

Current results from above code:

[3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39]

Note: this is not the actual range. It is much bigger, so if someone knows of a more efficient way, please let me know. — Duane Barker
– Duane Barker, Commented Sep 25, 2019 at 1:02

Green Cloak Guy · Accepted Answer · 2019-09-25 01:04:59Z

2

This should work:

L1, H1 = 3, 20
L2, H2 = 22, 40

new_list = [int(str(a) + str(b)) for a in range(L1, H1) for b in range(L2, H2)]
print(new_list)

# [322, 323, ..., 339, 422, 423, ..., 439, 522, ..., 939, 1022, 1023, ..., 1939]

It's a kind of hacky workaround for your kind of hacky use case: for each pair of numbers a and b from your two ranges, we

Convert a and b to strings
Concatenate them (so a=3 and b=22 produces '322')
Convert the result back into an integer

answered Sep 25, 2019 at 1:04

Green Cloak Guy

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3 Comments

Duane Barker Over a year ago

Okay so i tried the line below since memory will be an issue but still ran into MemoryError. new_list = tuple((int(str(a) + str(b)) for a,b in itertools.product(range(L1, H1), range(L2, H2))))

Green Cloak Guy Over a year ago

If your goal is to print out the numbers, rather than store them, then don't do tuple. Just do new_list = (int(str(a) + str(b)) for a in range(L1, H1) for b in range(L2, H2)) - with just the parentheses, and not a tuple(), it produces a generator that doesn't take constant memory. Thereafter you can do a for loop: for n in new_list: print(n)

Duane Barker Over a year ago

i'm getting "<generator object <genexpr> at 0x019610B0>" as a result

John Coleman · Accepted Answer · 2019-09-25 01:14:25Z

2

You are talking about the product of two lists, so an itertools solution would look like:

[int(str(a) + str(b)) for a,b in itertools.product(range(L1, H1), range(L2, H2))]

Note that your chain is superfluous and can simply be dropped. Also, if the ranges are large so that memory becomes an issue, you could use the generator expression

(int(str(a) + str(b)) for a,b in itertools.product(range(L1, H1), range(L2, H2)))

since in many ways the point of itertools is to allow for memory-efficient iteration.

edited Sep 25, 2019 at 1:14

answered Sep 25, 2019 at 1:07

John Coleman

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