Parsing a date that can be in several formats in python

Question

I would like to parse a date that can come in several formats, that I know beforehand. If I could not parse, I return nil. In ruby, I do like this:

DATE_FORMATS = ['%m/%d/%Y %I:%M:%S %p', '%Y/%m/%d %H:%M:%S', '%d/%m/%Y %H:%M', '%m/%d/%Y', '%Y/%m/%d']

def parse_or_nil(date_str)
    parsed_date = nil
    DATE_FORMATS.each do |f|
        parsed_date ||= DateTime.strptime(date_str, f) rescue nil
    end
    parsed_date
end

This is concise and works. How can I do the same thing in Python?

Answer 1

I would just try dateutil. It can recognize most of the formats:

from dateutil import parser
parser.parse(string)

if you end up using datetime.strptime as suggested @RocketDonkey:

from datetime import datetime

def func(s,flist):
    for f in flist:
        try:
            return datetime.strptime(s,f)
        except ValueError:
            pass

Answer 2

You can use try/except to catch the ValueError that would occur when trying to use a non-matching format. As @Bakuriu mentions, you can stop the iteration when you find a match to avoid the unnecessary parsing, and then define your behavior when my_date doesn't get defined because not matching formats are found:

You can use try/except to catch the ValueError that would occur when trying to use a non-matching format:

from datetime import datetime

DATE_FORMATS = ['%m/%d/%Y %I:%M:%S %p', '%Y/%m/%d %H:%M:%S', '%d/%m/%Y %H:%M', '%m/%d/%Y', '%Y/%m/%d']
test_date = '2012/1/1 12:32:11'

for date_format in DATE_FORMATS:
    try:
        my_date = datetime.strptime(test_date, date_format)
    except ValueError:
        pass
    else:
      break
else:
  my_date = None

print my_date # 2012-01-01 12:32:11
print type(my_date) # <type 'datetime.datetime'>

Answer 3

After your tip, RocketDonkey, and the one from Bakuriu, I could write a shorter version. Any problem with it?

def parse_or_none(date):
    for date_format in DATE_FORMATS:
        try:
            return datetime.strptime(date, date_format)
        except ValueError:
            pass
    return None

Answer 4

Modifying root's answer to handle m/d/y:

from dateutil import parser
parser.parse(string, dayfirst=False)

There's also a yearfirst option, to prefer y/m/d.