python sort date

[DeaD_EyE]

from datetime import datetime


def parse_datetime(line):
    date_str, _ = line.split(maxsplit=1)
    date_fmt = "%Y/%m/%d:%H:%M:%S"
    return datetime.strptime(date_str, date_fmt)


with open("in.txt") as fd:
    for line in sorted(fd, key=parse_datetime, reverse=True):
        # line is still a str
        print(line.strip())
        # print(line, end="")

This will still fail with corrupt data.
You can catch these errors and return datetime.min, which is the earliest possible date represented by datetime.

def parse_datetime(line):
    date_fmt = "%Y/%m/%d:%H:%M:%S"
    try:
        date_str, _ = line.split(maxsplit=1)
        return datetime.strptime(date_str, date_fmt)
    except ValueError:
        # invalid format
        return datetime.min
        # datetime.min == datetime.datetime(1, 1, 1, 0, 0)
        # used as minimum value
        # you can't mix if you sort, so all elements must be a datetime

• fd (the file object) is an iterator. Iterating over the fd will split the lines.
  
• sort(fd) will sort all lines of the whole file in lexicographical order.
  
• The key function of sort return a datetime object.
  
• sorting requires comparison. Python has a strong TypeSafety, so you can't for example compare an int with a str. But you can ship around with the key function, which always return the same type.
  
  If you want to put the data into a data-structure (e.g. a dict or namedtuple), I would do the parsing first, put this data into a list and sort the list, when everything has been finished.