Make an infinite list of natural numbers pasted together and find index python

Question

I need to make an infinite list of numbers and list them like this:

[12345678910111213141516171819...]

or

[1,2,3,4,5,6,7,8,9,1,1,1,2,1,3,1,4,1,5,1,6,1,7,1,8,1,8,9....]

So that the numbers are pasted together and can be separately indexed(find the position of a number eg. 15th number would be 2)

So the user would have to input some numbers like

15 2022 1410169200 2147483646

and my program would output

2 0 1 2

I understand now that I can't use some sort of big list, but have to make a searching algorithm of sorts?

Could anyone help?

Answer 1

I have to say that as hard as it is: You cannot have an infinite list in python. Python's lists actually require the storage for each element. Since there's no machine with infinite memory, there's no infinite python list.

However, what you can do is two things:

1. write a function that maps a natural number (what you call index) to a natural number in (0;10). Writing that function is rather easy. You know how many numbers of each length in digits there are, so finding the right answer doesn't actually require having a pre-generated list -- it can be done for every index you actually require
2. you can use that very same function to implement a [], though that is somewhat of a more advanced python feature.

EDIT:

Definitely don't go for a huge list! Just write a function that based on what the user enters returns the right digit... you know there's 9 numbers with 1 digit, there's 100-10 numbers with two digits, there's 10^3-10^2 numbers with three digits and so on. Write down the number of digits in your list on a piece of paper using normal math notation, and you'll quickly develop a method to get the 15001st digit in your list without having to calculate all the 15000 before it

Answer 2

I'm not sure to understand, you can't list infinity, just chuck norris can do it! :p More seriously, your command can't stop because infinity never stop so it's infinite loop. If you want you can list a lot of number for example:

big_list = [i for i in range(10000000)]

But I'm afraid you can't do better...

Answer 3

Apart from the obvious problems with infinity in finite space this might be what you want.

list = []
for x in xrange(100):   # You could put any number you want until you hit memory limit
    var = 'stored data ' + str(x**2)    # stores text and a math function
    list.append(var)    # Append simply adds current value to the end of the list
    print list[x]    #prints your value for debug purposes

This will create an indexed list withh all the interated data you want, to get your indexed data just type

print list[5] # or whatever number you want. You could also loop through it
for n in xrange(len(list) / 4): print list[x*4] # prints every fourth value

The while version would be:

x = 10
while x == 10: list.append('your data')

But it will just hit memory limit and crash.

Answer 4

You can do this sort of thing with a generator. Look at the function with yield below.

def natural_numbers():
    n = 0
    while True:
        n += 1
        yield n

def find_nth_character(n):
    numbers = ""
    gen = natural_numbers()

    while len(numbers) < n:
        numbers += str(gen.next())

    print numbers
    return numbers[n-1]


def main():
    print find_nth_character(15)

if __name__ == '__main__':
    main()

This code just stores a big string. If you're going to be looking for a very high index number, you'll probably want to find some other method for counting the number of characters. Then you can discard the characters before your target, and don't have to worry about storing a potentially huge string.