Nested Regular Expression in Python for

Question

Is there a way to do nested regular expression in Python? For example I have

r1 = re.compile(r'SO ON')

can I have something like

r2 = re.compile(r'WHATEVER AND (r1)*')

to validate "WHATEVER AND SO ON" for this example.

I tried finding about this around but couldn't find any solution.

Does making each pattern a string and concatenating them not work? — Justin Jasmann
– Justin Jasmann, Commented Mar 2, 2014 at 0:37
Yeah but that might be limited functionality to what a string can hold.. — Jack Smother
– Jack Smother, Commented Mar 2, 2014 at 0:43

U2EF1 · Accepted Answer · 2014-03-02 02:19:17Z

1

r1 = re.compile(r'SO ON')
r2 = re.compile(r'WHATEVER AND (%s)*' % r1.pattern)

This isn't actually using any special feature of regex, it's using string formatting. Multiple strings can be passed in as:

r'WHATEVER AND (%s) (%s)' % (r1.pattern, 'hello')

edited Mar 2, 2014 at 2:19

answered Mar 2, 2014 at 0:38

U2EF1

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3 Comments

Jack Smother Over a year ago

Thanks. I know about * to give random example to the question and what the ability of the nested regex is. Will accept when available. Thank you!

Jack Smother Over a year ago

#U2EF1 What would be the syntax to do more than one regex? Or is that not possible? r2 = re.compile(r'WHATEVER AND (%s)*' % r1.pattern, % r3.pattern)

SethMMorton Over a year ago

I feel a moral obligation to point out that this example uses old-style string formatting, and the wave of the future in python is to use new-style string formatting, as in r2 = re.compile(r'WHATEVER AND ({})*'.format(r1.pattern)) There are many reasons why this is superior to the old-style syntax. To read them look here.

whereisalext · Accepted Answer · 2016-09-05 17:27:03Z

0

I feel a moral obligation to point out that this is strictly supportive of regexen with no flags. As soon as you start using flags like re.MULTILINE this approach does not work. Perl was great with regex inside regex. I wish I could find a good Python solution.

answered Sep 5, 2016 at 17:27

whereisalext

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