I am trying to convert the date format '31-Dec-09' to '2009-12-31' in Python with the following code:
df = ['19-Jan-19', '4-Jan-19']
f = [datetime.datetime.strptime(x,'%d-%mmm-%y').strftime('%Y-%m-%d') for x in df]
print(f)
Getting the following error:
time data '9-Jan-19' does not match format '%d-%mmm-%y'
I have read somewhere that matching a two-digit year '00' would require a lowercase y instead of an upper case one. Either way, I am getting the same error so I guess something else is wrong. Any help?
Your %y and %Y patterns are fine, the issue is that you used %mmm here. The datetime.strptime() method patterns are all single letter patterns, and %mmm is seen as the %m pattern followed by two literal m characters. %m matches a numeric month (1 or 2 digits, zero-padding optional). So 19-1mm-19 would match, but 19-Jan-19 does not because the month is not numeric and the two literal m characters are missing.
The correct pattern to use is '%d-%b-%y' here, where %b matches an abbreviated month name.
Demo:
>>> import datetime
>>> df = ['19-Jan-19', '4-Jan-19']
>>> [datetime.datetime.strptime(x,'%d-%b-%y').strftime('%Y-%m-%d') for x in df]
['2019-01-19', '2019-01-04']
When trying to write such patterns, set yourself down with the Python REPL and try out partial inputs, try out the documented format codes for just that part of your input, and see what comes out. Make sure you use inputs other than the first of January 1900 (1900-01-01), so you can see the difference from the default:
>>> from datetime import datetime
>>> datetime.strptime("4", "%d")
datetime.datetime(1900, 1, 4, 0, 0)
>>> datetime.strptime("4-Feb", "%d-%b")
datetime.datetime(1900, 2, 4, 0, 0)
>>> datetime.strptime("4-Feb-19", "%d-%b-%y")
datetime.datetime(2019, 2, 4, 0, 0)