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Python Dates and Times in Python (2014) Let's Build a Timed Quiz App Harder Time Machine

Posted by john larson
john larson
16,594 Points

In researching how to solve this code challenge, I came across this and I passed but I don't really get it

import datetime

starter = datetime.datetime(2015, 10, 21, 16, 29)


def time_machine(integer, time_unit):
    if time_unit == "years":
        integer, time_unit = integer * 365, "days"
#  I was trying to get variables to work for the value in timedelta,
#  but it didn't work till I tried what appears to be unpacking
#  Though it doesn't seem to be the same as  unpacking a dictionary 
#  I would love some clarity on this, insights welcome :D 
    return starter + datetime.timedelta(**{time_unit : integer})

1 Answer

Kenneth Love
STAFF
Kenneth Love
Treehouse Guest Teacher
Kenneth Love
Kenneth Love
Treehouse Guest Teacher

The ** unpacks the dictionary into key=value pairs. Since all of the units, other than "years", are valid as keywords, this is a solid shortcut to the function.

Here's an example:

time_unit = "minutes"
integer = 5

When you call time_machine(integer, time_unit) and it gets to that last line (because time_unit isn't "years"), Python creates a new dictionary with {"minutes": 5} and then unpacks that into a minutes=5 argument for the datetime.timedelta call.

john larson
john larson
16,594 Points

Thanks Kenneth. It sounds like your saying that key=value pairs are always considered a dictionary? (this may be an understood concept that I'm just starting to get)

Kenneth Love
Kenneth Love
Treehouse Guest Teacher
Kenneth Love
Kenneth Love
Treehouse Guest Teacher

Uh, no.

If I create a function and use **kwargs as one of the parameters:

def some_function(name, **kwargs):

Then any key=value pairs that come in will be put into (packed) the kwargs dictionary.

If I have a dictionary that I want to use the key/value pairs of as arguments, I can unpack the dict into key=value arguments when I call a function:

some_function("Kenneth", **{"age": "thirty-something", "job": "teacher"})

That's the same as doing:

some_function("Kenneth", age="thirty-something", job="teacher")

but I can do it without knowing all of the keys/values beforehand.