Calculate date 5 days from today, adding an extra day for each day in the next 5 days that is a weekend day

Question

I am testing using Robot Framework and need to create my own Python keyword.

Taking the current date as day 0 (tomorrow as day 1), I am trying to calculate what the date will be 5 days from today. If any of the days in the next 5 days is a Saturday I need to add an extra day to my calculation. Same if any of the days is a Sunday.

As a Python beginner, I'm a little out of my depth so any help would be much appreciated

Answer 1

Basically you need to add 5 business days... This should do it:

import datetime
def addBusinessDays(from_date, add_days):
    business_days_to_add = add_days
    current_date = from_date
    while business_days_to_add > 0:
        current_date += datetime.timedelta(days=1)
        weekday = current_date.weekday()
        if weekday >= 5: # sunday = 6
            continue
        business_days_to_add -= 1
    return current_date

#demo:
print '5 business days from today:'
print addBusinessDays(datetime.date.today(), 5)

Update:

Here is the explanation:

1. We get the start date(Date that we need to add business days to it)
2. We use a loop to add days 1 at a time to the date(we use datetime.timedelta(days=1) to add 1 day to date)
3. After adding each day we check to see if updated date is weekday. If it's weekday we count it otherwise we don't count it and continue

Answer 2

You can do it mathematically:

from datetime import timedelta

def business_days(date, days):
    if days == 0:
        return date
    day = date.weekday()
    if day in (5, 6):
        date += timedelta(days=7 - day)
        days -= 1
    date += timedelta(days=days / 5 * 7)
    return date + timedelta(days=days % 5)

It will work to get a date n business days from or since whatever date you pass in:

In [6]: dte = datetime.datetime.today()

In [7]: business_days(dte, 5)
Out[7]: datetime.datetime(2016, 1, 6, 11, 28, 38, 264331)

In [8]: business_days(dte, -5)
Out[8]: datetime.datetime(2015, 12, 23, 11, 28, 38, 264331)

Answer 3

Using NumPy, you can find add or subtract business days using np.busday_offset:

Since 2016-03-27 is a Sunday, rolling forward returns the first valid business day, 2016-03-28:

import numpy as np
np.busday_offset('2016-03-27', 0, roll='forward')
# numpy.datetime64('2016-03-28')

To obtain a datetime object, call item():

np.busday_offset('2016-03-27', 0, roll='forward').item()
# datetime.date(2016, 3, 28)

To advance 5 business days, change the second argument to 5:

np.busday_offset('2016-03-27', 5, roll='forward').item()
# datetime.date(2016, 4, 4)

To go back 5 business days, use a negative offset and roll='backward':

np.busday_offset('2016-03-27', -5, roll='backward').item()
# datetime.date(2016, 3, 18)

np.busday_offset('2016-03-28', -5, roll='backward').item()
# datetime.date(2016, 3, 21)

---

Here's a calendar for reference:

      March 2016               April 2016         
 Su Mo Tu We Th Fr Sa     Su Mo Tu We Th Fr Sa    
        1  2  3  4  5                     1  2    
  6  7  8  9 10 11 12      3  4  5  6  7  8  9    
 13 14 15 16 17 18 19     10 11 12 13 14 15 16    
 20 21 22 23 24 25 26     17 18 19 20 21 22 23    
 27 28 29 30 31           24 25 26 27 28 29 30    

Answer 4

If you want to work with a lot of timeseries, have a look at pandas. Adding five business days is quite straightforward:

from datetime import datetime
import pandas as pd

today = datetime.today()
then = today + pd.tseries.offsets.BDay(5)