How to extract specific information with capture groups from an input string, rearrange and replace back inside this string using re.sub() function?

Question

import re

input_text = "estoy segura que empezaria desde las 15:00 pm del 2002_-_11_-_01 hasta las 16:00 hs pm" #example 1
input_text = "estoy segura que empezara desde las 15:00 pm h.s. del 2002_-_11_-_(01_--_15) hasta las 16:10 pm hs, aunque no se cuando podria acabar" #example 2
input_text = "probablemente dure desde las 01:00 am hasta las 16:00 pm del 2002_-_11_-_01 pero seguramente no mucho mas que eso" #example 3
input_text = "desde las 11:00 am hasta las 16:00 pm del 2002_-_11_-_(01_--_17) o quizas desde las 15:00 pm hs hasta las 16:00 pm del 2003_-_11_-_(01_--_17)" #example 4

def standardize_time_interval_associated_to_date(input_text, identify_only_4_digit_years = True):

    if   (identify_only_4_digit_years == True):  
        date_format_capture_01 = r"(\d{4})_-_(\d{2})_-_(\d{2})"
        date_format_capture_02 = r"(\d{4})_-_(\d{2})_-_\((\d{1,2})_--_(\d{1,2})\)"
    elif (identify_only_4_digit_years == False): 
        date_format_capture_01 = r"(\d*)_-_(\d{2})_-_(\d{2})"
        date_format_capture_02 = r"(\d*)_-_(\d{2})_-_\((\d{1,2})_--_(\d{1,2})\)"

    time_format_capture = r"(\d{1,2})[\s|:](\d{0,2})\s*(?:h.s.|h.s|hs|)\s*(?:(am)|(pm))\s*(?:h.s.|h.s|hs|)"



    #replace for the example 1
    input_text = re.sub(r"(?:desde|a[\s|]*partir)[\s|]*(?:de|)[\s|]*(?:las|la|)[\s|]*" + time_format_capture + r"[\s|]*(del|de[\s|]*el|de )[\s|]*(?:" + date_format_capture_02 + r"|" + date_format_capture_01 + r")[\s|]*(?:hasta|al)[\s|]*(?:las|la|)[\s|]*" + time_format_capture,
                        print(lambda m: print(m[1]) ) , 
                        input_text)

    #replace for the example 2
    input_text = re.sub(r"(?:desde|a[\s|]*partir)[\s|]*(?:de|)[\s|]*(?:las|la|)[\s|]*" + time_format_capture + r"[\s|]*(?:hasta|al)[\s|]*(?:las|la|)[\s|]*" + time_format_capture + r"[\s|]*(del|de[\s|]*el|de )[\s|]*(?:" + date_format_capture_02 + r"|" + date_format_capture_01 + r")",
                        print(lambda m: print(m[1])) , 
                        input_text)

    return input_text


#Here I make the call to the function indicating the input string as the first parameter, and as the second I pass an indication about how it should identify the date information
input_text = standardize_time_interval_associated_to_date(input_text, True)

print(repr(input_text)) # --> output

What should I put in the second parameter of the re.sub() function instead of print(lambda m: print(m[1])) so that the following string replacements are possible?

Replacements are expected to comply with this substitution (generic) structure:

(YYYY_-_MM_-_DD hh:mm pm or am_--_hh:mm am or pm)

Bearing in mind that the goal of the program is to search and rearrange information in the main string, the output that I need to get in each of the input example strings:

"estoy segura que empezaria (2002_-_11_-_01 (15:00 pm_--_16:00 pm))" #for example 1

"estoy segura que empezara (2002_-_11_-_(01_--_15) (15:00 pm_--_16:10 pm)), aunque no se cuando podria acabar" #for example 2

"probablemente dure (2002_-_11_-_01 (01:00 am_--_16:00 pm)) pero seguramente no mucho mas que eso" #for example 3

"(2002_-_11_-_(01_--_17) (11:00 am_--_16:00 pm)) o quizas (2003_-_11_-_(01_--_17) (15:00 pm_--_16:00 pm))" #for example 4

score 1 · Accepted Answer · answered Jan 01 '23 at 16:35

First of all, don't wrap that lambda with print as then you are not passing the lambda function to sub, but the return value from executing print (which is None and not a function). Moreover, that print will print a function object which is not interesting.

A working callback function for example #1 would be:

lambda m: (f"({m[10]}_-_{m[11]}_-_{m[12]} ({m[1]}:{m[2]} {m[3] or m[4]}_---_{m[13]}:{m[14]} {m[15] or m[16]}))"),

But using a callback function is overkill when the only thing you need is combining the capture groups. For that you can use a replacement string that uses back-references. So instead of lambda, you could pass this string literal:

r"(\10_-_\11_-_\12 (\1:\2 \3\4_---_\13:\14 \15\16))"

So the thing is to find out which is the number of the capture group you need, and reproduce it with a backslash-escaped number.

I guess you get the pattern here and can also create an expression for other examples.

Thank you very much, the lambda function option worked perfectly for me, the one that did not work at all well and gave me the following error was the second option `raise s.error("invalid group reference %d" % index, pos) re.error: invalid group reference 13 at position 34` — Matt095, Jan 01 '23 at 19:56
That error means you executed it on a regex that has no capture group 13. But it worked fine on the first example for me. See it run [here](https://www.online-python.com/DM34JBjr0N) — trincot, Jan 01 '23 at 20:30

How to extract specific information with capture groups from an input string, rearrange and replace back inside this string using re.sub() function?

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