How do I validate a date string format in python?
I have a python method which accepts a date input as a string.
How do I add a validation to make sure the date string being passed to the method is in the ffg. format:
'YYYY-MM-DD'
if it's not, method should raise some sort of error
>>> import datetime
>>> def validate(date_text):
try:
datetime.datetime.strptime(date_text, '%Y-%m-%d')
except ValueError:
raise ValueError("Incorrect data format, should be YYYY-MM-DD")
>>> validate('2003-12-23')
>>> validate('2003-12-32')
Traceback (most recent call last):
File "<pyshell#20>", line 1, in <module>
validate('2003-12-32')
File "<pyshell#18>", line 5, in validate
raise ValueError("Incorrect data format, should be YYYY-MM-DD")
ValueError: Incorrect data format, should be YYYY-MM-DD
The Python dateutil
library is designed for this (and more). It will automatically convert this to a datetime
object for you and raise a ValueError
if it can't.
As an example:
>>> from dateutil.parser import parse
>>> parse("2003-09-25")
datetime.datetime(2003, 9, 25, 0, 0)
This raises a ValueError
if the date is not formatted correctly:
>>> parse("2003-09-251")
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/Users/jacinda/envs/dod-backend-dev/lib/python2.7/site-packages/dateutil/parser.py", line 720, in parse
return DEFAULTPARSER.parse(timestr, **kwargs)
File "/Users/jacinda/envs/dod-backend-dev/lib/python2.7/site-packages/dateutil/parser.py", line 317, in parse
ret = default.replace(**repl)
ValueError: day is out of range for month
dateutil
is also extremely useful if you start needing to parse other formats in the future, as it can handle most known formats intelligently and allows you to modify your specification: dateutil
parsing examples.
It also handles timezones if you need that.
Update based on comments: parse
also accepts the keyword argument dayfirst
which controls whether the day or month is expected to come first if a date is ambiguous. This defaults to False. E.g.
>>> parse('11/12/2001')
>>> datetime.datetime(2001, 11, 12, 0, 0) # Nov 12
>>> parse('11/12/2001', dayfirst=True)
>>> datetime.datetime(2001, 12, 11, 0, 0) # Dec 11