A calculation gives <type 'exceptions.TypeError'> unsupported operand type(s) for -: 'str' and 'str'

[mostwanted]

I am trying to calculate the number of days and use that value in another calculation in my database.

I used this method below which used to to work perfectly but todays its giving me an error

db.define_table('invoice',
                Field('loaning_date', 'date', label=SPAN('Date Loaned', _style="font-weight: bold;"), requires=IS_NOT_EMPTY()),
                Field('returning_date', 'date', label=SPAN('Date Returned', _style="font-weight: bold;"), requires=IS_NOT_EMPTY()),
                              #Number of days calculation
                Field('daysLoaned', compute=lambda r: (r['returning_date']-r['loaning_date']).days),
                Field('price', 'float', label=SPAN('Price', _style="font-weight: bold;"), requires=IS_MATCH('[0-9]+', error_message=T('Enter Money in Proper Figures'))),
                Field('totalPrice', compute=lambda r: float(r['price'])* int(r['daysLoaned']), label=SPAN('Total Price', _style="font-weight: bold;")))

Why am i getting this error? How do i rectify it, maybe i am missing something!

Regards;

Mostwanted

[villas]

Check in DB what kind of field is 'daysLoaned'.  Maybe it is defined as a Str field?

Try:  Field('daysLoaned', compute=lambda r: str(r['returning_date']-r['loaning_date']).days)

Just an idea...

[mostwanted]

My understanding of the error is that i can not subtract strings, which is true, but these fiends on which i am performing subtraction are dates and i was trying to pick their days when i put them into ().days  so they wont be treated as strings because they are date fields, i cant figure out why it is not working!

[Dave S]

On Tuesday, August 13, 2019 at 10:12:07 AM UTC-7, mostwanted wrote:

My understanding of the error is that i can not subtract strings, which is true, but these fiends on which i am performing subtraction are dates and i was trying to pick their days when i put them into ().days  so they wont be treated as strings because they are date fields, i cant figure out why it is not working!

They are date fields.  Subtract them directly to get a datetime.timedelta object:
    compute = lambda r: {tdelta = r.returning_date - r.loaning_date; return tdelta.days}
See Sec 8.1 (8.1.2, especially) of the Python standard Library

/dps

[mostwanted]

Someone suggested that i try this:

from datetime import datetime

(datetime.strptime(r['returning_date'], '%Y/%m/%d %H:%M') - datetime.strptime(r['loaning_date'], '%Y/%m/%d %H:%M')).days

and it solved the problem

https://stackoverflow.com/questions/57483293/how-to-calculate-the-number-of-days-between-dates-picked-on-a-date-picker-calend

Regards;

Mostwanted