How to apply a function to an element at a particular position in every tuple inside a tuple of tuples?

Question

I have this tuple of tuples;

Tuple = ( ('AA', 'BB', datetime.datetime(2014, 3, 2, 0, 0) ), ('CC', 'DD', datetime.datetime(2014, 3, 2, 0, 1) )  )

I want to convert it to look like this;

Output= ( ('AA', 'BB', '2014-3-2 00:00:00' ), ('CC', 'DD', '2014-3-2 00:00:00'  )

The 3rd element of each tuple is to be converted into a string representing the datetime. This can be done with something like this Tuple[0][2].strftime('%Y-%m-%d %H:%M:%S')

The problem which I am stuck at is how do I apply this function strftime() to the 3rd element of every tuple inside this tuple of tuples?

Answer 1

You'll have to generate the tuples again. You can do so with the following list comprehension.

>>> [(a, b, date.strftime('%Y-%m-%d %H:%M:%S')) for (a, b, date) in Tuple]
[('AA', 'BB', '2014-03-02 00:00:00'), ('CC', 'DD', '2014-03-02 00:01:00')]

If the end result needs to be a tuple, use tuple() . This one uses a generator expression, but basically works the same:

>>> tuple((a, b, date.strftime('%Y-%m-%d %H:%M:%S')) for (a, b, date) in Tuple)
(('AA', 'BB', '2014-03-02 00:00:00'), ('CC', 'DD', '2014-03-02 00:01:00'))

Answer 2

List comprehension as @msvalkon mentioned, or using map and lambda :

In [731]: map(lambda tup: (tup[0], tup[1], tup[2].strftime('%Y-%m-%d %H:%M:%S')), Tuple)
Out[731]: [('AA', 'BB', '2014-03-02 00:00:00'), ('CC', 'DD', '2014-03-02 00:01:00')]

Answer 3

Here's a generator function that does the trick.

import datetime

def convert_nested(nested_tuples):
    for a, b, time in nested_tuples:
        yield (a, b, time.strftime('%Y-%m-%d %H:%M:%S'))

if __name__ == '__main__':
    nested_tuples = (('AA', 'BB', datetime.datetime(2014, 3, 2, 0, 0)),
                     ('CC', 'DD', datetime.datetime(2014, 3, 2, 0, 1)))

    output = tuple(convert_nested(nested_tuples))

    print(output)

Or more concisely as a generator comprehension.

import datetime

if __name__ == '__main__':
    nested_tuples = (('AA', 'BB', datetime.datetime(2014, 3, 2, 0, 0)),
                     ('CC', 'DD', datetime.datetime(2014, 3, 2, 0, 1)))

    output = tuple((a, b, time.strftime('%Y-%m-%d %H:%M:%S')) 
                   for a, b, time in nested_tuples)

    print(output)