Python3 regex escape function

Question

So I am given a string of digits of variable length and I need to find all possible number combinations using the digits in that string where only the digits in between may be changed, for example:

if I am given 123, I need to find the combinations of 1x2y3 where x, y are any digits.

if I am given 5312, I need to find the combinations of 5a3b1c2 where a, b, c are any digits.

I'm thinking this is possible using python's re.escape function, this is as far as I've come:

#Given the digits '123' from STDIN

#create a string "1\d2\d3"
my_regex_string = '\d'.join(input().split())

#Set x as starting point, set y as limit (not the most efficient)
x = 10**(len(my_regex_string)-1) * int(my_regex_string[0])
y = 10**(len(my_regex_string)-1) * (int(my_regex_string[0]) + 1)

while x < y:
    if bool(re.match(re.escape(p), str(x)))
        print(x)
    x+=1

I need feedback, does my approach make sense? Is this task doable with regex or do I need another approach?

Using regex for this is a really bad choice. Use itertools.product. — wolfrevokcats
– wolfrevokcats, Commented Apr 18, 2018 at 19:31
Are you trying to find the total number, or get a list of all solutions? — Sunny Patel
– Sunny Patel, Commented Apr 18, 2018 at 20:11
Are you looking to create a regex that can just match these combinations, or to just create the combinations ? A regex would be 1\d2\d3, etc. To generate, its just simple nested loops that you don't need anything special to do it with. — user557597
– user557597, Commented Apr 18, 2018 at 20:55

Sadiq · Accepted Answer · 2018-04-18 19:59:52Z

3

I think, like what the wolfrevokcats said, the pythonic way of doing this is to use itertools.product function. Something like this code:

from itertools import product

s = input()
r = "{}".join(list(s))
c = [int(r.format(*f)) for f in product(range(0,10), repeat=len(s)-1)]

answered Apr 18, 2018 at 19:59

Sadiq

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1 Comment

Jonathan R Over a year ago

Really clean solution! Good job

Jonathan R · Accepted Answer · 2018-04-18 20:00:28Z

1

Here's one solution using itertools, probably not the most sophisticated but it works:

>>> import itertools
>>> x = map(lambda z: [s[i] + str(z[i]) for i in range(len(s)-1)] + [s[-1]], list(itertools.product(range(10), repeat=len(s)-1)))
>>> y = map(lambda z: "".join(z), x)
>>> list(y)

answered Apr 18, 2018 at 20:00

Jonathan R

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