import re
import sys
from collections import namedtuple

# Simple data objects are handy as hell. Use more of them.

Month = namedtuple('Month', 'name number days')
Culture = namedtuple('Culture', 'format separator indexes regex')
Date = namedtuple('Date', 'year month day')

Months = (
    Month('January', 1, 31),
    Month('February', 2, 28),
    Month('March', 3, 31),
    Month('April', 4, 30),
    Month('May', 5, 31),
    Month('June', 6, 30),
    Month('July', 7, 31),
    Month('August', 8, 31),
    Month('September', 9, 30),
    Month('October', 10, 31),
    Month('November', 11, 30),
    Month('December', 12, 31),
)

Cultures = (
    Culture('yyyy-MM-dd',    '-', (0,1,2), '^\d{4}\-0?([2-9]|1[0-2]?)\-(0?(3[01]|[12][0-9]|[1-9]))$'),
    Culture('yyyy/MM/dd',    '/', (0,1,2), '^\d{4}\/0?([2-9]|1[0-2]?)\/(0?(3[01]|[12][0-9]|[1-9]))$'),
    Culture('MM/dd/yyyy',    '/', (2,0,1), '^0?([2-9]|1[0-2]?)\/(0?(3[01]|[12][0-9]|[1-9]))\/\d{4}$'),
    Culture('MMM dd, yyyy',  ' ', (2,0,1), '^[A-Za-z]{3} (0?(3[01]|[12][0-9]|[1-9])), \d{4}$'),
    Culture('dd MMM, yyyy',  ' ', (2,1,0), '^(0?(3[01]|[12][0-9]|[1-9])) [A-Za-z]{3}, \d{4}$'),
    Culture('MMMM dd, yyyy', ' ', (2,0,1), '^[A-Za-z]{3,9} (0?(3[01]|[12][0-9]|[1-9])), \d{4}$'),
    Culture('dd MMMM, yyyy', ' ', (2,1,0), '^(0?(3[01]|[12][0-9]|[1-9])) [A-Za-z]{3,9}, \d{4}$'),
    Culture('yyyy, MMM dd',  ' ', (0,1,2), '^\d{4}, [A-Za-z]{3} (0?(3[01]|[12][0-9]|[1-9]))$'),
    Culture('yyyy, MMMM dd', ' ', (0,1,2), '^\d{4}, [A-Za-z]{3,9} (0?(3[01]|[12][0-9]|[1-9]))$'),
)

# A purely stylistic point: organize modules the way you want to read them.
# Most humans like to read things top to bottom.

def main(args):
    start, end = args
    ddate = diffdate(start, end)
    print(ddate)

def diffdate(start, end):
    d1 = totaldays(parsedate(start))
    d2 = totaldays(parsedate(end))
    return d2 - d1

def totaldays(date):
    y = date.year
    if date.month <= 2:
        y -= 1
    leaps = y // 4 - y // 100 + y // 400
    m = sum(Months[b].days for b in range(date.month - 1))
    days = (date.year - 1) * 365 + m + date.day + leaps
    return days

def parsedate(date):
    for c in Cultures:
        if re.match(c.regex, date):
            parts = date.replace(',', '').split(c.separator)
            year = int(parts[c.indexes[0]])
            month = parsemonth(parts[c.indexes[1]])
            day = int(parts[c.indexes[2]])
            return Date(year, month, day)
    # Raise an error if we get here.

def parsemonth(month):
    if month.isdigit():
        return int(month)
    else:
        for m in Months:
            if m.name.lower().startswith(month.lower()):
                return m.number
    # Raise an error if we get here.

if __name__ == '__main__':
    main(sys.argv[1:])

import re
import sys
from collections import namedtuple

# Simple data objects are handy as hell. Use more of them.

Month = namedtuple('Month', 'name number days')
Culture = namedtuple('Culture', 'format separator indexes regex')
Date = namedtuple('Date', 'year month day')

Months = (
    Month('January', 1, 31),
    Month('February', 2, 28),
    Month('March', 3, 31),
    Month('April', 4, 30),
    Month('May', 5, 31),
    Month('June', 6, 30),
    Month('July', 7, 31),
    Month('August', 8, 31),
    Month('September', 9, 30),
    Month('October', 10, 31),
    Month('November', 11, 30),
    Month('December', 12, 31),
)

Cultures = (
    Culture('yyyy-MM-dd',    '-', (0,1,2), '^\d{4}\-0?([2-9]|1[0-2]?)\-(0?(3[01]|[12][0-9]|[1-9]))$'),
    Culture('yyyy/MM/dd',    '/', (0,1,2), '^\d{4}\/0?([2-9]|1[0-2]?)\/(0?(3[01]|[12][0-9]|[1-9]))$'),
    Culture('MM/dd/yyyy',    '/', (2,0,1), '^0?([2-9]|1[0-2]?)\/(0?(3[01]|[12][0-9]|[1-9]))\/\d{4}$'),
    Culture('MMM dd, yyyy',  ' ', (2,0,1), '^[A-Za-z]{3} (0?(3[01]|[12][0-9]|[1-9])), \d{4}$'),
    Culture('dd MMM, yyyy',  ' ', (2,1,0), '^(0?(3[01]|[12][0-9]|[1-9])) [A-Za-z]{3}, \d{4}$'),
    Culture('MMMM dd, yyyy', ' ', (2,0,1), '^[A-Za-z]{3,9} (0?(3[01]|[12][0-9]|[1-9])), \d{4}$'),
    Culture('dd MMMM, yyyy', ' ', (2,1,0), '^(0?(3[01]|[12][0-9]|[1-9])) [A-Za-z]{3,9}, \d{4}$'),
    Culture('yyyy, MMM dd',  ' ', (0,1,2), '^\d{4}, [A-Za-z]{3} (0?(3[01]|[12][0-9]|[1-9]))$'),
    Culture('yyyy, MMMM dd', ' ', (0,1,2), '^\d{4}, [A-Za-z]{3,9} (0?(3[01]|[12][0-9]|[1-9]))$'),
)

# A purely stylistic point: organize modules the way you want to read them.
# Most humans like to read things top to bottom.

def main(args):
    start, end = args
    ddate = diffdate(start, end)
    print(ddate)

def diffdate(start, end):
    d1 = totaldays(parsedate(start))
    d2 = totaldays(parsedate(end))
    return d2 - d1

def totaldays(date):
    y = date.year
    if date.month <= 2:
        y -= 1
    leaps = y // 4 - y // 100 + y // 400
    m = sum(Months[b].days for b in range(date.month - 1))
    days = (date.year - 1) * 365 + m + date.day + leaps
    return days

def parsedate(date):
    for c in Cultures:
        if re.match(c.regex, date):
            parts = date.replace(',', '').split(c.separator)
            return Date(
                int(parts[c.indexes[0]]),
                parsemonth(parts[c.indexes[1]]),
                int(parts[c.indexes[2]]),
            )
    # Raise an error if we get here.

def parsemonth(month):
    if month.isdigit():
        return int(month)
    else:
        for m in Months:
            if m.name.lower().startswith(month.lower()):
                return m.number
    # Raise an error if we get here.

if __name__ == '__main__':
    main(sys.argv[1:])

Another case in point: don't drive your algorithm with data that requires parsing. For example, if you think you need a tuple of indexes like (2, 0, 1), don't store it in a comma-delimited string and complicate your algorithmic code with the unpacking logic. Just store the indexes directly as a tuple of integers. The core problem in software writing is reducing and managing complexity, and the greatest complexity is always algorithmic, and it's usually lumpy, in the sense of being concentrated in specific parts of a program. Investing more in creating "smarter" or "richer" data will help you keep the algorithmic parts of the code easier to understand and maintain.

After the simplification from those changes are made, the splitter() function seems unnecessary. Instead, I would suggest a different helper function just to parse the month. And that logic doesn't require regex: you can use simpler things like isdigit() and startswith(). Also, a Month should know its number. Again, use richer data to simplify algorithm. After 30 years of writing code, that's my top piece of advice.

• If you invest more in your regular expressions so that they use named captures, you can drop the tedious details in Culture.separator and Culture.indexes. Instead, you can grab the year, month, and day directly from the re.Match object, by name. Again, smart data, simple code.

• When given invalid input, your code just blows up. Give some thought to whether you want to invest in better error handling/reporting.

• Dates are notoriously complicated. There are probably weird edge-case bugs in your code. Are you sure you don't want to use datetime?

Another case in point: don't drive your algorithm with data that requires parsing. For example, if you think you need a tuple of indexes like (2, 0, 1), don't store it in a comma-delimited string and complicate your algorithmic code with the unpacking logic. Just store the indexes directly as a tuple of integers. The core problem in software writing is reducing and managing complexity, and the greatest complexity is always algorithmic. Investing more in creating "smarter" or "richer" data will help you keep the algorithmic parts of the code easier to understand and maintain.

After the simplification from those changes are made, the splitter() function seems unnecessary. Instead, I would suggest a different helper function just to parse the month. And that logic doesn't require regex: you can use simpler things like isdigit() and startswith(). Also, a Month should know its number. Again, use richer data to simplify algorithm.

• If you invest more in your regular expressions so that they use named captures, you can drop the tedious details in Culture.separator and Culture.indexes. Instead, you can grab the year, month, and day directly from the re.Match object, by name. Yet again, smart data, simple code.

• When given invalid input, your code just blows up. Give some thought to whether you want to invest in better error handling/reporting.

• Dates are notoriously complicated. There are probably weird edge-case bugs in your code. Are you sure you don't want to use datetime?