Group naming with group and nested regex (unit conversion from text file)

Question

Basic Question:

How can you name a python regex group with another group value and nest this within a larger regex group?

Origin of Question:

Given a string such as 'Your favorite song is 1 hour 23 seconds long. My phone only records for 1 h 30 mins and 10 secs.'

What is an elegant solution for extracting the times and converted to a given unit?

Attempted Solution:

My best guess at a solution would be to create a dictionary and then perform operations on the dictionary to convert to the desired unit.

i.e. convert the given string to this:

string[0]:
 {'time1': {'day':0, 'hour':1, 'minutes':0, 'seconds':23, 'milliseconds':0}, 'time2': {'day':0, 'hour':1, 'minutes':30, 'seconds':10, 'milliseconds':0}}

string[1]:
 {'time1': {'day':4, 'hour':2, 'minutes':3, 'seconds':6, 'milliseconds':30}}

I have a regex solution, but it isn't doing what I would like:

import re

test_string = ['Your favorite song is 1 hour 23 seconds long.  My phone only records for 1h 30 mins and 10 secs.',
                'This video is 4 days 2h 3min 6sec 30ms']

year_units = ['year', 'years', 'y']
day_units = ['day', 'days', 'd']
hour_units = ['hour', 'hours', 'h']
min_units = ['minute', 'minutes', 'min', 'mins', 'm']
sec_units = ['second', 'seconds', 'sec', 'secs', 's']
millisec_units = ['millisecond', 'milliseconds', 'millisec', 'millisecs', 'ms']
all_units = '|'.join(year_units + day_units + hour_units + min_units + sec_units + millisec_units)
print((all_units))

# pattern = r"""(?P<time>               # time group beginning
#               (?P<value>[\d]+)    # value of time unit
#               \s*                 # may or may not be space between digit and unit
#               (?P<unit>%s)        # unit measurement of time
#               \s*                 # may or may not be space between digit and unit
#           )
#           \w+""" % all_units
pattern = r""".*(?P<time>       # time group beginning
            (?P<value>[\d]+)    # value of time unit
            \s*                 # may or may not be space between digit and unit
            (?P<unit>%s)        # unit measurement of time
            \s*                 # may or may not be space between digit and unit
            ).*                 # may be words in between the times 
            """ % (all_units)

regex = re.compile(pattern)
for val in test_string:
    match = regex.search(val)
    print(match)
    print(match.groupdict())

This fails miserably due to not being able to properly deal with nested groupings and not being able to assign a name with the value of a group.

Answer 1

First of all, you can't just write a multiline regex with comments and expect it to match anything if you don't use the re.VERBOSE flag:

regex = re.compile(pattern, re.VERBOSE)

---

Like you said, the best solution is probably to use a dict

for val in test_string:
    while True: #find all times
        match = regex.search(val) #find the first unit
        if not match:
            break
        matches= {} # keep track of all units and their values
        while True:
            matches[match.group('unit')]= int(match.group('value')) # add the match to the dict
            val= val[match.end():] # remove part of the string so subsequent matches must start at index 0
            m= regex.search(val)
            if not m or m.start()!=0: # if there are no more matches or there's text between this match and the next, abort
                break
            match= m
        print matches # the finished dict

# output will be like {'h': 1, 'secs': 10, 'mins': 30}

However, the code above won't work just yet. We need to make two adjustments:

• The pattern cannot allow just any text between matches. To allow only whitespace and the word "and" between two matches, you can use

  pattern = r"""(?P<time> # time group beginning (?P<value>[\d]+) # value of time unit \s* # may or may not be space between digit and unit (?P<unit>%s) # unit measurement of time \s* # may or may not be space between digit and unit (?:\band\s+)? # allow the word "and" between numbers ) # may be words in between the times """ % (all_units)

• You have to change the order of your units like so:

  year_units = ['years', 'year', 'y'] # yearS before year day_units = ['days', 'day', 'd'] # dayS before day, etc...

  Why? Because if you have a text like 3 years and 1 day, then it would match 3 year instead of 3 years and.