Specific data conversion in python

Question

I have dates in the form given below:

   "1###-##-##" here # denote uncertainty. e.g.

   "1###-##-##" denotes (1000-00-00 to 1999-12-31)
   "-138 - ## - ##" denotes (0138-01-01 BC, 0138-12-31 BC) 
   "18##-##-##" denotes (1800-01-01, 1899-12-31)
   "1713-##-##" denotes (1713-01-01, 1713-12-31)
   "####-##-##" denotes (0001-01-01, 9999-12-31)

I tried to achieve this conversion by using specific switch cases which did not turn out to be efficient. Is there some other means in python by which I may achieve this?

Here below zero values are converted to BC

EDIT: My desired output is given a pattern like "1###-##-##" find out the minimum and maximum range

What is your desired output? It's not exactly clear. A tuple with minimum and maximum dates? — Ofir Israel
– Ofir Israel, Commented Sep 25, 2013 at 22:58
@OfirIsrael My desired output is given a pattern like "1*--**" find out the minimum and maximum range — Jannat Arora
– Jannat Arora, Commented Sep 25, 2013 at 23:15

Veedrac · Accepted Answer · 2013-09-25 23:17:23Z

Given

dateranges = [
    "1***-**-**", 
    "-138 - ## - ##",
    "18##-##-##",
    "1713-##-##",
    "####-##-##"
]

your best parser will probably be re, assuming that you don't want to do this properly:

import re
matcher = re.compile("(-?[\d*#]+)\s*-\s*([\d*#][\d*#])\s*-\s*([\d*#][\d*#])")

datetuples = [matcher.match(daterange).groups() for daterange in dateranges]

And then you can just go through the tuples,

for year, month, day in datetuples:

convert each unknown to a digit and cap.

    minyear  = int(year.replace("*", "0").replace("#", "0"))
    minmonth = max(1, int(month.replace("*", "0").replace("#", "0")))
    minday   = max(1, int(day.replace("*", "0").replace("#", "0")))

    mindate = (minyear, minmonth, minday)

    maxyear  = int(year.replace("*", "9").replace("#", "9"))
    maxmonth = min(12, int(month.replace("*", "9").replace("#", "9")))
    ### WARNING! MAXIMUM DAY NUMBER DEPENDS ON BOTH MONTH AND YEAR
    maxday  = min(31, int(day.replace("*", "9").replace("#", "9")))

    maxdate = (maxyear, maxmonth, maxday)

    print(mindate, maxdate)

#>>> (1000, 1, 1) (1999, 12, 31)
#>>> (-138, 1, 1) (-138, 12, 31)
#>>> (1800, 1, 1) (1899, 12, 31)
#>>> (1713, 1, 1) (1713, 12, 31)
#>>> (0, 1, 1) (9999, 12, 31)

Bear in mind that this accepts false positives due to the cap and also bear in mind the big, bold warning.

Trevor Merrifield · Accepted Answer · 2013-09-26 00:25:34Z

If I understand correctly you want * to denote a range from 0 to the maximum value, and # to denote a range from 1 to the maximum value. Further, a date that starts with a dash is in BC.

Is this any better than your original approach?

def getdaterange(inputdate):
    inputdate = inputdate.replace(' ', '')

    maxdate = '9999-12-31'
    zerodate = '0000-00-00'
    onedate = '0001-01-01'

    lowdate = list(inputdate)
    highdate = list(inputdate)

    for i, ch in enumerate(inputdate):
        if ch == '*' or ch == '#':
            highdate[i] = maxdate[i]

        if ch == '*':
            lowdate[i] = zerodate[i]
        elif ch == '#':
            lowdate[i] = onedate[i]

    if inputdate[0] == '-':
        lowdate[0], highdate[0] = '0', '0'
        lowdate.append(' BC')
        highdate.append(' BC')

    return (''.join(lowdate), ''.join(highdate))

testins = ('1***-**-**', '-138 - ## - ##', '18##-##-##',
            '1713-##-##', '####-##-##')
for i in testins:
    print(getdaterange(i))

The outputs look correct.

('1000-00-00', '1999-12-31')
('0138-01-01 BC', '0138-12-31 BC')
('1801-01-01', '1899-12-31')
('1713-01-01', '1713-12-31')
('0001-01-01', '9999-12-31')

Of course it doesn't validate input to the function. It may be worth adding some regex to the beginning to verify the input is in the right form.

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