How to format date string via multiple formats in python

I have three date formats: YYYY-MM-DD, DD.MM.YYYY, DD/MM/YYYY.

Is it possible to validate and parse strings such as 2014-05-18 or 18.5.2014 or 18/05/2019?

Try each format and see if it works:

from datetime import datetime

def try_parsing_date(text):
    for fmt in ('%Y-%m-%d', '%d.%m.%Y', '%d/%m/%Y'):
        try:
            return datetime.strptime(text, fmt)
        except ValueError:
            pass
    raise ValueError('no valid date format found')

>>> import dateutil.parser
>>> dateutil.parser.parse(date_string)

This should take care of most of the standard date formats in Python 2.7+. If you really have super custom date formats, you can always fall back to the one mentioned by Jon Clements.

This actually a problem i was facing and this how i approached it, my main purpose was to the date seperators

class InputRequest:
     "This class contain all inputs function that will be required in this program. "

      def __init__(self, stockTickerName = 'YHOO', stockSite='yahoo', startDate = None, 
             endDate = datetime.date.today()):

      def requestInput(self, requestType =''):
          "Fro requesting input from user"
          self.__requestInput = input(requestType)
          return self.__requestInput


def dateFormat(self, dateType=''):
    '''
        this function handles user date input
        this repeats until the correct format is supplied
        dataType: this is the type of date, eg: DOF, Date of Arriveal, etc 

    '''
    while True:
        try:
            dateString = InputRequest.requestInput(self,dateType)
            dtFormat = ('%Y/%m/%d','%Y-%m-%d','%Y.%m.%d','%Y,%m,%d','%Y\%m\%d') #you can add extra formats needed
            for i in dtFormat:
                try:
                    return datetime.datetime.strptime(dateString, i).strftime(i)
                except ValueError:
                    pass
                
        except ValueError:
            pass
        print('\nNo valid date format found. Try again:')
        print("Date must be seperated by either [/ - , . \] (eg: 2012/12/31 --> ): ")

In order to add a bit to @jon-clements already great answer,

added some verbosity on the exception raised for traceability purposes

from datetime import datetime

def try_parsing_date(possible_date, field):
	"""
	Try to parse a date using several formats, warn about
	problematic value if the possible_date does not match
	any of the formats tried
	"""
	for fmt in ('%Y-%m-%d', '%d/%m/%Y', '%m/%d/%Y'):
		try:
			return datetime.strptime(possible_date, fmt)
		except ValueError:
			pass
	raise ValueError(f"Non-valid date format for field {field}: '{possible_date}'")

Here, possible_date is the text that may contain a date in one of the formats, and field would be the variable or column that you are testing. This makes it easier to find the problematic value

Pure python:

from datetime import datetime
my_datetime = datetime.strptime('2014-05-18', '%Y-%m-%d') 
repr(my_datetime)

>>> 'datetime.datetime(2014,5,18,0,0)'

Check datetime.strptime() format documentation for more format strings.