How to join subsequent digits in a Python list into a double (or more) digit number

Question

I have the following string:

string = 'TAA15=ATT'

I make a list out of it:

string_list = list(string)
print(string_list)

and the result is:

['T', 'A', 'A', '1', '5','=', 'A', 'T', 'T']

I need to detect subsequent digits and join them into a single number, as shown below:

['T', 'A', 'A', '15','=', 'A', 'T', 'T']

I'm also quite concerned with performances. This string conversion is done thousand times.

Thank you for any hints you can provide.

Answer 1

Here is a very short solution

import re

def digitsMerger(source):
    return re.findall(r'\d+|.', source)

digitsMerger('TAA15=ATT')
['T', 'A', 'A', '15', '=', 'A', 'T', 'T']

Answer 2

Using itertools.groupby

Ex:

from itertools import groupby
string = 'TAA15=ATT'

result = []
for k, v in groupby(string, str.isdigit):
    if k:
        result.append("".join(v))
    else:
        result.extend(v)
print(result)

Output:

['T', 'A', 'A', '15', '=', 'A', 'T', 'T']

Answer 3

Another regexp:

import re

s = 'TAA15=ATT'

pattern = r'\d+|\D'

m = re.findall(pattern, s)

print(m)

Answer 4

You can use regular expressions, in Python the library re :

import re
string = 'TAA15=ATT'
num = re.sub('[^0-9,]', "", string)
pos = string.find(num)
str2 = re.sub('\\d+',"", string)
str2 = re.sub('=',"", str2)
print(str2)
l = list()
for el in str2:
    l.append(el)
l.insert(pos, num)
print(l)

Basically re.sub('[^0-9,]', "", string) is telling: take the string, match all the characters that are not ( ^ means negation) numbers ( 0-9 ) and substitute them with the second parameter, ie., an empty string. So basically what's left are only digits that you have to convert to an integer.

If the = is always after the digit instead of

str2 = re.sub('\\d+',"", string)
str2 = re.sub('=',"", str2)

you can do

str2 = re.sub('\\d+=',"", string)

Answer 5

You can create a function that compares the last value seen and the next and use functools.reduce :

from functools import reduce

string_list = ['T', 'A', 'A', '1', '5', 'A', 'T', 'T']

def combine_nums(lst, nxt):
    if lst and all(map(str.isdigit, (lst[-1], nxt))):
        nxt = lst[-1] + nxt
    return lst + [nxt]

print(reduce(combine_nums, string_list, [])

Results:

['T', 'A', 'A', '1', '15', 'A', 'T', 'T']