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

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'>