How to Split a String Between Numbers and Letters?

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Problem Formulation: Given a string of letters and numbers. How to split the string into substrings of either letters or numbers by using the boundary between a letter and a number and vice versa.

Examples: Have a look at the following examples of what you want to accomplish.

'111A222B333C'     --->    ['111', 'A', '222', 'B', '333', 'C']
'Finxter42'        --->    ['Finxter', '42']
'Hello world'     --->    ['Hello', ' world']

Method 1: re.split()

The re.split(pattern, string) method matches all occurrences of the pattern in the string and divides the string along the matches resulting in a list of strings between the matches. For example, re.split('a', 'bbabbbab') results in the list of strings ['bb', 'bbb', 'b'].

# Method 1: re.split()
import re
s = '111A222B333C'
res = re.split('(\d+)', s)
print(res)
# ['', '111', 'A', '222', 'B', '333', ' C']

The \d special character matches any digit between 0 and 9. By using the maximal number of digits as a delimiter, you split along the digit-word boundary. Note that you don’t consume the split character by wrapping it into a matching group using the parentheses (...). If you leave out the parentheses, it’ll consume the numbers and the result wouldn’t contain any consecutive numbers.

Method 2: re.findall()

The re.findall(pattern, string) method scans string from left to right, searching for all non-overlapping matches of the pattern. It returns a list of strings in the matching order when scanning the string from left to right.

# Method 2: re.findall()
import re
s = '111A222B333C'

res = re.findall('(\d+|[A-Za-z]+)', s)

print(res)
# ['111', 'A', '222', 'B', '333', 'C']

Method 3: itertools.groupby()

# Method 3: itertools.groupby()
from itertools import groupby
s = '111A222B333C'

res = [''.join(g) for _, g in groupby(s, str.isalpha)]
print(res)
# ['111', 'A', '222', 'B', '333', 'C']
  • The itertools.groupby(iterable, key=None) function creates an iterator that returns tuples (key, group-iterator) grouped by each value of key. We use the str.isalpha() function as key function.
  • The str.isalpha() function returns True if the string consists only of alphabetic characters.

Related Video re.split()

Programmer Humor

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~~~

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