Given a date format and a string date, the task is to write a python program to check if the date is valid and matches the format.
Examples:
Input : test_str = ’04-01-1997′, format = “%d-%m-%Y”
Output : True
Explanation : Formats match with date.
Input : test_str = ’04-14-1997′, format = “%d-%m-%Y”
Output : False
Explanation : Month cannot be 14.
Method #1 : Using strptime()
In this, the function, strptime usually used for conversion of string date to datetime object, is used as when it doesn’t match the format or date, raises the ValueError, and hence can be used to compute for validity.
Python3
# Python3 code to demonstrate working of# Validate String date format# Using strptime()from datetime import datetime# initializing stringtest_str = '04-01-1997'# printing original stringprint("The original string is : " + str(test_str))# initializing formatformat = "%d-%m-%Y"# checking if format matches the dateres = True# using try-except to check for truth valuetry: res = bool(datetime.strptime(test_str, format))except ValueError: res = False# printing resultprint("Does date match format? : " + str(res)) |
Output:
The original string is : 04-01-1997 Does date match format? : True
Method #2 : Using dateutil.parser.parse()
In this, we check for validated format using different inbuilt function, dateutil.parser. This doesn’t need the format to detect for a date.
Python3
# Python3 code to demonstrate working of# Validate String date format# Using dateutil.parser.parsefrom dateutil import parser# initializing stringtest_str = '04-01-1997'# printing original stringprint("The original string is : " + str(test_str))# initializing formatformat = "%d-%m-%Y"# checking if format matches the dateres = True# using try-except to check for truth valuetry: res = bool(parser.parse(test_str))except ValueError: res = False# printing resultprint("Does date match format? : " + str(res)) |
Output:
The original string is : 04-01-1997 Does date match format? : True
Method#3: Using regular expression
Approach
validate a string date format is by using regular expressions. We can define a regular expression pattern that matches the expected format, and then use the re module to check if the string matches the pattern.
Algorithm
1. Import the re module
2. Define the input test string and the regular expression pattern string
3. Use the re.match() method to match the pattern against the test string
4. If the pattern matches the test string:
a. Print “True”
5. Otherwise:
a. Print “False”
Python3
import retest_str = '04-01-1997'pattern_str = r'^\d{2}-\d{2}-\d{4}$'if re.match(pattern_str, test_str): print("True")else: print("False") |
True
Time complexity of this approach is O(n), where n is the length of the input string.
Auxiliary Space is also O(n), since we need to store the regular expression pattern in memory.
