I'm new to python and I'm looking to work with datetime. I have some files generated every Sunday and I like to move the furthest Sunday out of the current folder eg: 2020-04-12, 2020-04-19, 2020-04-26.
I have found some examples on getting a specific date from today's date and I was able to modify it a tab bit. Eg. I can go back and get last week's Sunday with a specific date:
from datetime import date
from datetime import timedelta
import datetime
today = datetime.datetime(2020,4,13)
offset = (today.weekday() + 1) % 7
sunday = today - timedelta(days=offset)
#print (offset)
print(sunday)
I am confused by the offset variable. What is (today.weekday() + 1) % 7 doing? I have read the Python doc and not quite wrapping my head around it. With +1, I get the date 2020-04-12, which is a Sunday, great. When I do -1 (the other thing is if I set it to (today.weekday() - 1) % 7), I get 2020-04-07, a Tuesday. How did it jump from Sunday the 12th to Tuesday the 7th?
Additionally, how do I get it to jump back 3 weeks? that's where I'm also stuck.
Alright, so if today's Wednesday, then today.weekday() is 2, because it starts counting from 0 on Monday. Not sure why, but that's life.
So (2 + 1) % 7) = 3. That means that 3 days ago was Sunday. Hence your code:
offset = (today.weekday() + 1) % 7 # How many days ago was sunday
sunday = today - timedelta(days=offset) # Go backwards from today that many days
You'll notice that if you subtract one instead of add one, that means we're going backwards (because we're sutracting the timedelta object) by two fewer days than before (because 2 - 1 is equivalent to (2 + 1) - 2, that is, two fewer days). If you started by going backwards enough days to get to Sunday, and now you're going backwards two fewer days, you'll end up on Tuesday, which is two days later than Sunday.
The easiest way to shift which week you're headed to is to set the weeks argument in timedelta:
n_weeks = 3
sunday = today - timedelta(days=offset, weeks=n_weeks)
that's equivalent to, but much prettier than:
sunday = today - timedelta(days=offset + n_weeks * 7)
Related
Problem Statement:
Am developing a custom job scheduler that needs to be run on given days. It takes start date and end date as string and third param is list of week days on which job should run.
Start day can be different with given days but first job should run on next valid day
Let suppose Start date is 2022-09-07 (so day name is Wednesday) but given frequency days are ["Monday", "Friday", "Saturday"] so i need to run my first job on coming Friday and for this i need to calculate difference between start date and first valid day (in this case it's Friday)
So how can i do this python to run my first job on valid day (that can be in any position of given frequency days list) and also after one job complete i need to also get next valid day. I did some work but unfortunately its not working. Here is what i did
sorted_week_days_list = ['Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday', 'Sunday']
start_date = "2022-09-07"
valid_frequency_days = ["Monday", "Tuesday", "Friday"] # It can be any days in sorted order
start_date_object = datetime.datetime.strptime(start_date, "%Y-%m-%d")
given_start_day = start_date_object.strftime("%A")
if given_start_day not in valid_frequency_days:
# Need help to implement logic to get date for valid day
You should use the datetime.weekday() method to pull out the day of the week for days of interest. Assuming that you have dates similar to the format you show above, it is easy to convert, and also just use the day index for your "allowable start days" (Monday=0).
Then you can jig up a little function to look for the next start date in your sorted list and figure out how many days you need to wait.
Example below does that and also "rolls over" the weekend as needed.
Code:
from datetime import datetime, timedelta
from bisect import bisect_left
start_date = "2022-09-09"
valid_start_dates = [1, 4] # It can be any days in sorted order
start_date_object = datetime.strptime(start_date, "%Y-%m-%d")
d=start_date_object.weekday()
print(f'the numbered day of the week is: {d}')
def days_till_start(day, valid_start_days):
idx = bisect_left(valid_start_days, day)
if idx >= len(valid_start_days): # wrap around to next start
return valid_start_days[0] + 7 - day
elif day == valid_start_days[idx]:
return 0
else:
return valid_start_days[idx] - day
print(days_till_start(d, valid_start_dates))
start_dates = ['2022-09-05', '2022-09-06', '2022-09-07', '2022-09-08', '2022-09-09', '2022-09-10']
start_wkdys = [datetime.strptime(d, "%Y-%m-%d").weekday() for d in start_dates]
for d in start_wkdys:
print(f'day index is: {d}')
print(f'next start date is {days_till_start(d, valid_start_dates)} away')
print()
Output:
the numbered day of the week is: 4
0
day index is: 0
next start date is 1 away
day index is: 1
next start date is 0 away
day index is: 2
next start date is 2 away
day index is: 3
next start date is 1 away
day index is: 4
next start date is 0 away
day index is: 5
next start date is 3 away
We can find different approaches to determining the week of the month, and even though there are many pages on 1:4 and/or 1:5, there is very few around 1:6 approach.
So to give you a bit of the context, I am working with a pivot table in Excel which gets its values from a Power Query source.
In Power Query, there is a function Date.WeekOfMonth which takes in the date and returns a number between 1 and 6.
In this definition, weeks start from Sunday and ends on Saturday.
So, for example, the first two days of October 2021 -i.e. Fri & Sat- fall in the 1st week of Oct, while the 3rd day of Oct 2021 starts the second week, and then the last day of October 2021,i.e. Oct 31, is the only day in the 6th week.
I had an automation task on hand in which I needed to pull data from the Power Query-generated pivot, so I had to implement a piece of code in VBA which calcs weeks the same.
Unfortunately, I couldn't find any prepared snippet, so after implementing I though it might worth sharing.
(Any comments and suggestions appreciated)
The DatePart function is perfect for this. Using DatePart with the interval set to "weeks" you can find the week of a given date. Then you subtract the number of weeks before the first day of that month (which sets the first day to week = 1).
Function WeekNumOfDate(D As Date) As Integer
WeekNumOfDate = DatePart("ww", D) - DatePart("ww", DateSerial(Year(D), Month(D), 1)) + 1
End Function
Here is a second version of the function that has the ability to set the FirstDayOfWeek argument:
Function WeekNumOfDate(D As Date, Optional FirstDayOfWeek As VbDayOfWeek = vbSunday) As Integer
WeekNumOfDate = DatePart("ww", D, FirstDayOfWeek) - DatePart("ww", DateSerial(Year(D), Month(D), 1), FirstDayOfWeek) + 1
End Function
As an example for using FirstDayOfWeek: With FirstDayOfWeek set to vbThursday, the date "Nov 5th, 2021" will return as Week 2, whereas it would by default be counted as Week 1. November 1st to 3rd of 2021 will be week 1, and then 4th to 10th will be week 2.
Its implementation in VBA is:
Function WeekOfMonth(My_Date As Date)
If Day(My_Date) > Day(My_Date - 1) And Weekday(My_Date) > Weekday(My_Date - 1) Then
WeekOfMonth = WeekOfMonth(My_Date - 1)
ElseIf Day(My_Date) > Day(My_Date - 1) And Weekday(My_Date) < Weekday(My_Date - 1) Then
WeekOfMonth = WeekOfMonth(My_Date - 1) + 1
Else
WeekOfMonth = 1
End If
End Function
Note that even though the above function is recursive, its time and space complexity is an expression of order N, which here cannot exceed 31.
I have 2 columns with timestamp on them, I need the difference between them in seconds in a 3rd column , excluding weekends. How am I supposed to do this in Python/pandas?
I want it to exclude Saturday/Sunday from the timeline.
Ex -
1 . Starts at Thursday/Friday and ends at Monday/Tuesday - Calculate duration only for the time it lied between Thursday/Friday and then directly Monday/Tuesday.
2 . If it starts on Saturday and ends on Monday - Calculate only for Monday.
3 . If ex.Starts on Friday and ends on Sunday, Calculate only for Friday.
4 . If starts and ends on Saturday and Sunday - result is 0 seconds
First, Convert the timestamp in both the columns to DateTime if not it's already in this format.
Second, find if the day is a weekend or a weekday and use total_seconds method to find the diff in seconds in the following way:
def find_diff_in_secs(row):
day_of_week = row["start"].weekday()
if day_of_week<5:
# Find the diff in secs
diff_in_secs =(row["end"]-row["start"]).total_seconds()
return diff_in_secs
else:
return "NA"
df.apply(find_diff_in_secs)
What I want to do is figure out what X of the month this is, and returning the relative delta constant for it (Su Mo Tu...). I have found many examples of jumping to a specific day of the month (1). For instance today is the 3rd Tuesday of December and I can get to it by doing this: + relativedelta(month=12, day=1, weekday=TU(3))) but what I want to do is the opposite:
Put in today's date and subtract the first of the month and get something like TU(3) or if it were the 4th wednesday to get: WE(4)
My ultimate goal is to then be able to transfer this constant to a different month or timedelta object and find the equivalent 3rd Tuesday, or 4th Wednesday, etc...
This is a solution that I have come up with, maybe you'll find it less complicated.
It also seems to be about 4 times faster, which if you process a lot of dates can make a difference.
from datetime import *
from dateutil.relativedelta import *
def weekDayOfTheMonth(xdate):
daylist = [MO,TU,WE,TH,FR,SA,SU]
weekday = xdate.weekday()
firstDayOfTheMonth = datetime(xdate.year, xdate.month, 1)
interval = (weekday + 7 - firstDayOfTheMonth.weekday() ) % 7
firstOfThisWeekDay = datetime(xdate.year, xdate.month, 1 + interval)
n = ((xdate.day - firstOfThisWeekDay.day) / 7) + 1
return daylist[weekday](n)
print(weekDayOfTheMonth(datetime.today()))
print(weekDayOfTheMonth(datetime(2018,11,24)))
Basically what happens is that:
I find what day of the week is the first day of given month.
Based on that information I can easily calculate first day of any given weekday in given month.
Then I can even more easily calculate that for example 18th of December 2018 is third Tuesday of this month.
Ok I found a way using rrule to create a list of days in the month that share the current weekday up until today, then length of this list becomes the Nth. Than I use a list as a lookup table for the weekday constants. Not tested to see if this will work for every day of the month but this is a start.
from datetime import *; from dateutil.relativedelta import *
from dateutil.rrule import rrule, WEEKLY
import calendar
def dayofthemonth(xdate):
daylist = [MO,TU,WE,TH,FR,SA,SU]
thisweekday = daylist[xdate.weekday()]
thisdaylist = list(rrule(freq=WEEKLY, dtstart=xdate+relativedelta(day=1), until=xdate, byweekday=xdate.weekday()))
return thisweekday(len(thisdaylist))
print(dayofthemonth(datetime.today())) #correctly returns TU(+3) for 2018, 12, 18
I am writing code that lets users write down dates and times for things they have on. It takes in the date on which it starts, the start time and finish time. It also allows the user to specify if they want it to carry over into multiple weeks (every Monday for a month for example)
I am using a for loop to do this, and because of the different months having different days I obviously want (if the next Monday for example is in the next month) it to have the correct date.
This is my code:
for i in range(0 , times):
day = day
month = month
fulldateadd = datetime.date(year, month, day)
day = day + 7
if month == ( '01' or '03' or '05' or '07' or '10'or '12'):
if day > 31:
print(day)
day = day - 31
print(day)
month = month + 1
elif month == ( '04' or '06'or '09' or '11'):
if day > 30:
print(day)
day = day - 30
print(day)
month = month + 1
elif month == '02':
if day > 29:
print(day)
day = day - 29
print(day)
month = month + 1
When running this and testing to see if it goes correctly into the new month I get the error:
File "C:\Users\dansi\AppData\Local\Programs\Python\Python36-32\gui test 3.py", line 73, in addtimeslot
fulldateadd = datetime.date(year, month, day)
ValueError: day is out of range for month
Where have I gone wrong?
It's hard to be completely accurate without seeing some of the previous code (for example, where do day, month, year, and times come from?), but here's how you might be able to use timedelta in your code:
fulldateadd = datetime.date(year, month, day)
for i in range(times):
fulldateadd = fulldateadd + datetime.timedelta(7)
A timedelta instance represents a period of time, rather than a specific absolute time. By default, a single integer passed to the constructor represents a number of days. So timedelta(7) gives you an object that represents 7 days.
timedelta instances can then be used with datetime or date instances using basic arithmetic. For example, date(2016, 12, 31) + timedelta(1) would give you date(2017, 1, 1) without you needing to do anything special.