Doctest with datetime

Question

I have done a search but could not find what I was after.

My code is as followed:

import datetime
import doctest
import os


def parseOptions():

    import optparse
    parser = optparse.OptionParser(usage= '-h')
    parser.add_option('-d', '--difference', \
                      type= 'int')
    (options, args) = parser.parse_args()
    return options

now = datetime.datetime.now()
subtract = datetime.timedelta(days=10, hours=11)
difference = now - subtract

def checktime(now - b):
    """Returns a - b

    >>> checktime(now - 10)
    'now - 10'

    >>> checktime(now - 20)
    'now - 20'

    >>> checktime(now - 30)
    'now - 30'
    """
    return now - b

if__name__== "__main__":
    doctest.testmod()


print
print 'The time now is =', now.strftime("%I:%M:%S%p %a, %B %d %Y")
print 'The time minus the difference =', difference.strftime("%I:%M:%S%p %a, %B %d %Y")
print

I want the doctest to test that the time now minus the number (10, 20, 30 in hours) is giving the correct output before proceeding.

When I run the script in command prompt I get the following mesage:

2 items had no tests:
    time
    time.struct_time
0 tests in 2 items.
0 passed and 0 failed.
Test passed.

I have attempted to changes bits and pieces to find what is being defined with time and time.struct_time and have failed miserably.

Any help would be greatly appreciated!

Answer 1

Doctest is useful if you want to test that the function is doing what was intended. In your case, I presume you want to subtract b hours from the datetime argument and return the difference.

Re-writing your function to subtime

def subtime(a,b):
    subtract = datetime.timedelta(hours=b)
    difference = a - subtract
    return difference

To run doctests, you'll need to provide some sample calling values and the expected results. Think about the corner cases for your function (Places where something wierd might happen). Now let us form some test-cases

1. Subtract less than 24 hours
2. Subtract exactly 24 hours
3. Subtract more than 24 hours
4. Subtract 0 hours
5. Add some hours (-ve arguments)

Now write down how the function will be called in each case. Use the same datetime as first argument for simplicity. (Do not use script variables such as now because you cannot predict their values when the script runs)

1. subtime(datetime.datetime(2013,11,11,11,0),10)
2. subtime(datetime.datetime(2013,11,11,11,0),24)
3. subtime(datetime.datetime(2013,11,11,11,0),30)
4. subtime(datetime.datetime(2013,11,11,11,0),0)
5. subtime(datetime.datetime(2013,11,11,11,0),-5)

Now calculate (using a pen and paper) what should be the ideal result for each case

1. datetime.datetime(2013, 11, 11, 1, 0)
2. datetime.datetime(2013, 11, 10, 11, 0)
3. datetime.datetime(2013, 11, 10, 5, 0)
4. datetime.datetime(2013, 11, 11, 11, 0)
5. datetime.datetime(2013, 11, 11, 16, 0)

Add this to your function in the documentation string """ """

def subtime(a,b):
    """ (datetime,int) -> datetime 
    Subtract b hours from a datetime.datetime and return the new datetime object

    >>> subtime(datetime.datetime(2013,11,11,11,0),10)
    datetime.datetime(2013, 11, 11, 1, 0)

    >>> subtime(datetime.datetime(2013,11,11,11,0),24)
    datetime.datetime(2013, 11, 10, 11, 0)

    >>> subtime(datetime.datetime(2013,11,11,11,0),30)
    datetime.datetime(2013, 11, 10, 5, 0)

    >>> subtime(datetime.datetime(2013,11,11,11,0),0)
    datetime.datetime(2013, 11, 11, 11, 0)

    >>> subtime(datetime.datetime(2013,11,11,11,0),-5)
    datetime.datetime(2013, 11, 11, 16, 0)

    """
    subtract = datetime.timedelta(hours=b)
    difference = now - subtract
    return difference

Your script now is

import datetime
import doctest
import os

def parseOptions():

    import optparse
    parser = optparse.OptionParser(usage= '-h')
    parser.add_option('-d', '--difference', \
                      type= 'int')
    (options, args) = parser.parse_args()
    return options
now = datetime.datetime.now()

def subtime(a,b):
    """ (datetime,int) -> datetime 
    Subtract b hours from a datetime.datetime and return the new datetime object

    >>> subtime(datetime.datetime(2013,11,11,11,0),10)
    datetime.datetime(2013, 11, 11, 1, 0)

    >>> subtime(datetime.datetime(2013,11,11,11,0),24)
    datetime.datetime(2013, 11, 10, 11, 0)

    >>> subtime(datetime.datetime(2013,11,11,11,0),30)
    datetime.datetime(2013, 11, 10, 5, 0)

    >>> subtime(datetime.datetime(2013,11,11,11,0),0)
    datetime.datetime(2013, 11, 11, 11, 0)

    >>> subtime(datetime.datetime(2013,11,11,11,0),-5)
    datetime.datetime(2013, 11, 11, 16, 0)

    """
    subtract = datetime.timedelta(hours=b)
    difference = a - subtract
    return difference

if __name__== "__main__":
    doctest.testmod()    

print
print 'This is the time now -', now.strftime("%I:%M:%S %p %a, %B %d %Y")
difference=subtime(now,10)
print 'This is the time minus the difference -', difference.strftime("%I:%M:%S %p %a, %B %d %Y")
print

And the output

$ python try.py 

This is the time now - 02:40:57 PM Tue, May 28 2013
This is the time minus the difference - 04:40:57 AM Tue, May 28 2013

Note that with doctest you won't get any test related output if all the tests pass. (Everything is OK)