issue converting bash script to python

Question

I have the following code in shell:

case ${daterange} in
  *[Mm][Oo]*)
    factor=2592000
    ;;
  *[Ww]*)
    factor=604800
    ;;
  *[Dd]*)
    factor=86400
    ;;
  *[Hh]*)
    factor=3600
    ;;
  *)
    factor=60
    ;;
esac
num=`expr x"$TMFR" : x"[^0-9]*\([0-9]*\)"`
expr 0$num \* $factor

I wrote the following to convert it into python, but where I get stuck is the num= and expr lines. I dont know how to transfer them to python.

    if re.search(r'[Mm][Oo]', daterange):
        print "A"
    elif re.search(r'[Ww]', daterange):
        print "B"
    elif re.search(r'[Dd]', daterange):
        print "C"
    elif re.search(r'[Hh]', daterange):
        print "D"
    elif re.search(r'[Mm]', daterange):
        print "E"
    else:
        print "F"

daterange can contain values such as:

4h = which means 4 hours
4mo = which means 4 months
4w = which means 4 weeks
4d = which means 4 days
4m = which means 4 minutes
4s = which means 4 seconds

The goal here is to take the value in daterange and translate it into seconds.

re.search() seems overkill, as if 'mo' in daterange.lower(): would work too. — Martijn Pieters
– Martijn Pieters, Commented Jun 23, 2018 at 19:00
Have you checked out what expr does? Type man expr in your shell. You have a STRING : REGEXP test, so the matched text is stored in num. — Martijn Pieters
– Martijn Pieters, Commented Jun 23, 2018 at 19:01
Can these duration strings appear multiple times? Should they be combined when they do? So 1mo 2w 3d is 1 month, 2 weeks, and 3 days, totaling 4060800 seconds? — Martijn Pieters
– Martijn Pieters, Commented Jun 23, 2018 at 19:15
Should repeated patterns with no spaces in between be supported? — Martijn Pieters
– Martijn Pieters, Commented Jun 23, 2018 at 19:20

Martijn Pieters · Accepted Answer · 2018-06-23 19:25:51Z

expr executes expressions:

expr x"$TMFR" : x"[^0-9]*$[0-9]*$" matches the string x followed by the value of $TMFR against the regulare expression x[^0-9]*([0-9]*), printing out the part between the parentheses (which are escaped to prevent them from being interpreted by bash instead).
expr 0$num \* $factor multiplies the number $num by $factor, defaulting to 0.

So it basically finds the first numeric value in the string $TMFR and multiplies that number by the factor already calculated.

If you always have a number followed by a duration string, I'd just use a regular expression to extract both in one go, and use a dictionary to map the duration string to a factor:

import re

durations = {
    'mo': 2592000,
    'w': 604800,
    'd': 86400,
    'h': 3600,
    'm': 60,
    's': 1
}
# match on digits followed directly by one of the duration strings, ignoring case
# the duration strings are sorted by descending length to ensure shorter
# sub-patterns are considered after the longer options (compare 'mo' and m')
pattern = re.compile(r'(\d+)({})\b'.format(
    '|'.join(sorted(durations, key=len, reverse=True))),
    flags=re.IGNORECASE) 

def duration_from_string(s):
    return sum(
        int(m.group(1)) * durations[m.group(2)]
        for m in pattern.finditer(s))

I've assumed you need to support compound durations that are space separated, so 1mo 2w 3d is 4060800 seconds (1 month, 2 weeks and 3 days):

>>> duration_from_string('foo bar spam 1mo 2w 3d')
4060800

If the format should work without spaces too, drop the \b anchor from the regex pattern.

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