sorting a list containing dates as a substring

Question

I have a list of strings something like this As you can make out there is a date embedded at the start of the string and also at the end of the string.

 a = ["08/19/2014100%ABC10/02/2014F","02/12/2012100%ABC10/02/2014F",
      "08/29/2014100%ABC10/02/2012F"]

I wanted to sort this list based on the date substring.

The way I wanted to implement is by extract the date, sort the date and join the date with the substring, but it's becoming too complicated.

Answer 1

Just call sorted() with the key argument set to a function that extracts and converts the date from the string into a datetime.datetime object.

>>> from datetime import datetime
>>> a = ["08/19/2014100%ABC10/02/2014F","02/12/2012100%ABC10/02/2014F", "08/29/2014100%ABC10/02/2012F"]
>>> sorted_a = sorted(a, key=lambda s: datetime.strptime(s[:10], '%m/%d/%Y'))
>>> sorted_a
['02/12/2012100%ABC10/02/2014F', '08/19/2014100%ABC10/02/2014F', '08/29/2014100%ABC10/02/2012F']

Or, if you want to sort in place:

>>> a.sort(key=lambda s: datetime.strptime(s[:10], '%m/%d/%Y'))
>>> a
['02/12/2012100%ABC10/02/2014F', '08/19/2014100%ABC10/02/2014F', '08/29/2014100%ABC10/02/2012F']

If you actually mean to sort on the last date in the string just change the key function to:

lambda s: datetime.strptime(s[-11:-1], '%m/%d/%Y')