Please explain the second line in below code

Question

Please explain the second line in below code

s = time.strftime("%Y_%m_%d")
theday = datetime.date(*map(int, s.split('_')))
previous_day = theday - datetime.timedelta(days=1)

Answer 1

hi Raj,

the line:

theday = datetime.date(*map(int, s.split('_')))

is doing this:
‘s’ is a string (2019_03_22) and will separated by the split function at the positions ‘_’. Now map is taking the 3 parts of splitted string and applies a function to each of them. Function used is ‘int()’. Map then returns a so called ‘map object’. This can not be printed as it is. So we use the ‘*’ operator which is an ‘unpack operator’ in this case.
I hope this sounds not too complicated.

Answer 2

hi Raj, I have added some print statements to your code that shows what happens.

import datetime
import time

s = time.strftime("%Y_%m_%d")
print(s)
print(type(s))
theday = datetime.date(*map(int, s.split('_')))
print(theday)
print(type(theday))
previous_day = theday - datetime.timedelta(days=1)
print(previous_day)

output:

2019_03_22
<class 'str'>
2019-03-22
<class 'datetime.date'>
2019-03-21

In the first line after imports s is creared as a string Y M D with _ as separator.
in the next line s wiil be split, converted to int and then converted to a datetime object. Then you can calculate with this object in the next line by subtracting -1. You can see what happens in the output.
Hope this helps.

Answer 3

*map why do we use it?