Convert \"unknown format\" strings to datetime objects in Python

Dates can be in many formats like "2009/05/13 19:19:30", "May 13 2009 07:19PM", and "2009-05-13 19:19". Python provides several approaches to convert these unknown format strings into datetime objects using the datetime and dateutil modules.

A Python datetime object contains complete information about date and time including year, month, day, hours, minutes, seconds, and time zones. This article shows how to convert unknown format date strings to datetime objects.

Input-Output Example

Here's what we want to achieve ?

Input string (unknown format): 20050607T090650
Output Datetime object: 2005-06-07 09:06:50
Data type: <class 'datetime.datetime'>

Using datetime.strptime() Method

The strptime() method parses a string into a datetime object using specific format codes.

Syntax

datetime.strptime(date_string, format_string)

Common Format Codes

Example 1: ISO Format with Timezone

from datetime import datetime

date_string = '20151002151700-0800'
print("Input string:", date_string)

obj = datetime.strptime(date_string, "%Y%m%d%H%M%S%z")
print("Output Datetime object:", obj)
print('Data type:', type(obj))

Input string: 20151002151700-0800
Output Datetime object: 2015-10-02 15:17:00-08:00
Data type: <class 'datetime.datetime'>

Example 2: Readable Format

from datetime import datetime

date_string = 'Wed Mar 16 16:12:05 2016 +0800'
print("Input string:", date_string)

obj = datetime.strptime(date_string, '%a %b %d %H:%M:%S %Y %z')
print("Output Datetime object:", obj)
print('Data type:', type(obj))

Input string: Wed Mar 16 16:12:05 2016 +0800
Output Datetime object: 2016-03-16 16:12:05+08:00
Data type: <class 'datetime.datetime'>

Using dateutil.parser.parse() Function

The dateutil library provides a more flexible parse() function that automatically detects date formats without specifying format codes.

Example 1: Automatic Format Detection

from dateutil.parser import parse

date_string = 'Wed Mar 16 16:12:05 2016 +0800'
print("Input string:", date_string)

obj = parse(date_string)
print("Output Datetime object:", obj)
print('Data type:', type(obj))

Input string: Wed Mar 16 16:12:05 2016 +0800
Output Datetime object: 2016-03-16 16:12:05+08:00
Data type: <class 'datetime.datetime'>

Example 2: Handling Ambiguous Dates

The parse() function has parameters like dayfirst to handle ambiguous dates ?

from dateutil.parser import parse

date_string = '06/07/2005'
print("Input string:", date_string)

# Default: month first (US format)
obj1 = parse(date_string)
print("Default parsing:", obj1)

# Day first (European format)
obj2 = parse(date_string, dayfirst=True)
print("Day first parsing:", obj2)

Input string: 06/07/2005
Default parsing: 2005-06-07 00:00:00
Day first parsing: 2005-07-06 00:00:00

Comparison

Conclusion

Use datetime.strptime() when you know the exact format for better performance. Use dateutil.parser.parse() for unknown or varying formats as it automatically detects the format and handles ambiguous dates.