Argparse to denote time period, in hours or days

Question

I am trying to write an argument (for argparse) in which, I am trying to define the inputs in terms of hours or days.

For example:

def setup_args():
    ....
    parser.add_argument(
        "--time",
        type=str,
        help="Define the time period (only hours or days). Eg. 3h or 3d"
    ) 

def time_input(user_input):
    if user_input.endswith('h'):
        ...
        # using datetime module to forward current time X hours later
    elif user_input.endswith('d'):
        ...
        # I may specify it to a max 2 days.
        # using datetime module to forward current time X days later

While the function I wrote works, I am wondering if there is a better way to approach this, or is using endswith the only way to go?

Answer 1

Maya might work for you:

>>> maya.when("in 1H").datetime()
datetime.datetime(2018, 6, 27, 22, 16, 42, 371621, tzinfo=<UTC>)
>>> maya.when("in 1 day").datetime()
datetime.datetime(2018, 6, 28, 21, 16, 42, 371621, tzinfo=<UTC>)

You may even specify arbitrary time values and not limit to only hours or days, which causes your app to be even more flexible:

>>> maya.when("now").datetime()
datetime.datetime(2018, 6, 27, 21, 20, 7, 409348, tzinfo=<UTC>)
>>> maya.when("in 1 hour 2 minutes").datetime()
datetime.datetime(2018, 6, 27, 22, 22, 7, 825372, tzinfo=<UTC>)

PS Maya is powered by dateparser . Although you can use dateparser straight out of the bat to handle everything, I think Maya will prove more useful.

Answer 2

A function like this, can be used as a type in argparse . It could also be used after parsing:

def period(astr):
    if astr.lower().endswith('h'):
        units = 'timedelta64[h]'
    elif astr.lower().endswith('d'):
        units = 'timedelta64[D]'
    else:
        raise argparse.ArgumentTypeError('wrong time units')
    return np.array(astr[:-1], dtype=units)

I defined it to return a numpy timedelta64 array, in part because I'm more familiar with it than with the Python timedelta , and it is easy to specify the time units:

In [249]: period('4h')
Out[249]: array(4, dtype='timedelta64[h]')
In [250]: period('3d')
Out[250]: array(3, dtype='timedelta64[D]')

tolist will extract it from the array and return a timedelta object.

In [251]: period('3d').tolist()
Out[251]: datetime.timedelta(3)
In [253]: period('3h').item()
Out[253]: datetime.timedelta(0, 10800)

The function could be changed to work with timedelta directly.

A parser could be:

In [239]: parser = argparse.ArgumentParser()
In [240]: parser.add_argument('--time', type=period, help='time delta');

testing:

In [241]: parser.parse_args('--time 3d'.split())
Out[241]: Namespace(time=array(3, dtype='timedelta64[D]'))
In [255]: parser.parse_args('--time 4h'.split())
Out[255]: Namespace(time=array(4, dtype='timedelta64[h]'))

errors:

In [256]: parser.parse_args('--time 4m'.split())
usage: ipython3 [-h] [--time TIME]
ipython3: error: argument --time: wrong time units
In [257]: parser.parse_args('--time 4.34d'.split())
usage: ipython3 [-h] [--time TIME]
ipython3: error: argument --time: invalid period value: '4.34d'