How to determine appropriate strftime format from a date string?

Question

The dateutil parser does a great job of correctly guessing the date and time from a wide variety of sources.

We are processing files in which each file

Answer 1

You can write your own parser:

import datetime

class DateFormatFinder:
    def __init__(self):
        self.fmts = []

    def add(self,fmt):
        self.fmts.append(fmt)

    def find(self, ss):
        for fmt in self.fmts:            
            try:
                datetime.datetime.strptime(ss, fmt)
                return fmt
            except:
                pass
        return None

You can use it as follows:

>>> df = DateFormatFinder()
>>> df.add('%m/%d/%y %H:%M')
>>> df.add('%m/%d/%y')
>>> df.add('%H:%M')

>>> df.find("01/02/06 16:30")
'%m/%d/%y %H:%M'
>>> df.find("01/02/06")
'%m/%d/%y'
>>> df.find("16:30")
'%H:%M'
>>> df.find("01/02/06 16:30")
'%m/%d/%y %H:%M'
>>> df.find("01/02/2006")

However, It is not so simple as dates can be ambiguous and their format can not be determined without some context.

>>> datetime.strptime("01/02/06 16:30", "%m/%d/%y %H:%M") # us format
datetime.datetime(2006, 1, 2, 16, 30)
>>> datetime.strptime("01/02/06 16:30", "%d/%m/%y %H:%M") # european format
datetime.datetime(2006, 2, 1, 16, 30)