How to use regular expression to separate numbers and characters in strings like "30M1000N20M"

Question

I'm trying to separate the [0-9] and [A-Z] in strings like these:

100M
20M1D80M
20M1I79M
20M10000N80M

I tried using the Python re module, and the following is the code I used:

>>>import re
>>>num_alpha = re.compile('(([0-9]+)([A-Z]))+')
>>>str1="100M"
>>>n_a_match = num_alpha.match(str1)
>>>n_a_match.group(2), n_a_match.group(3)

100,M   #just what I want

>>>str1="20M10000N80M"
>>>n_a_match = num_alpha.match(str1)
>>>n_a_match.groups()

('80M', '80', 'M')  #only the last one, how can I get the first two?
#expected result ('20M','20','M','10000N','10000','N','80M','80','M')

This regular expression works well for strings which contain only one match, but not several groups of matches. How can I handle that using regular expressions?

Answer 1

I suggest using re.findall. If you intend to iterate over the results, rather than building a list, you could use re.finditer instead. Here's an example of how that would work:

>>> re.findall("(([0-9]+)([A-Z]))", "20M10000N80M")
[('20M', '20', 'M'), ('10000N', '10000', 'N'), ('80M', '80', 'M')]

If you don't want the combined numbers+letters string, you can remove the outer parentheses from the match and just get the separate parts:

>>> re.findall("([0-9]+)([A-Z])", "20M10000N80M")
[('20', 'M'), ('10000', 'N'), ('80', 'M')]

Or, if you don't want tuples at all (and you don't need to worry about malformed input, such as strings with several letters in a row), you could change the pattern to an alternation, and get the values one by one:

>>> re.findall("([0-9]+|[A-Z])", "20M10000N80M")
['20', 'M', '10000', 'N', '80', 'M']