In Python, how do I find the date of the first Monday of a given week?
Question:
If I have a certain week number (eg 51) and a given year (eg 2008), how do I find the date of the first Monday of that same week?
Many thanks
Answers:
>>> import time
>>> time.asctime(time.strptime('2008 50 1', '%Y %W %w'))
'Mon Dec 15 00:00:00 2008'
Assuming the first day of your week is Monday, use %U instead of %W if the first day of your week is Sunday. See the documentation for strptime for details.
Update: Fixed week number. The %W directive is 0-based so week 51 would be entered as 50, not 51.
This seems to work, assuming week one can have a Monday falling on a day in the last year.
from datetime import date, timedelta
def get_first_dow(year, week):
d = date(year, 1, 1)
d = d - timedelta(d.weekday())
dlt = timedelta(days = (week - 1) * 7)
return d + dlt
Use the string formatting found in the time module. Detailed explanation of the formats used
>>> import time
>>> time.strptime("51 08 1","%U %y %w")
(2008, 12, 22, 0, 0, 0, 0, 357, -1)
The date returned is off by one week according to the calendar on my computer, maybe that is because weeks are indexed from 0?
PEZ’s and Gerald Kaszuba’s solutions work under assumption that January 1st will always be in the first week of a given year. This assumption is not correct for ISO calendar, see Python’s docs for reference. For example, in ISO calendar, week 1 of 2010 actually starts on Jan 4, and Jan 1 of 2010 is in week 53 of 2009. An ISO calendar-compatible solution:
from datetime import date, timedelta
def week_start_date(year, week):
d = date(year, 1, 1)
delta_days = d.isoweekday() - 1
delta_weeks = week
if year == d.isocalendar()[0]:
delta_weeks -= 1
delta = timedelta(days=-delta_days, weeks=delta_weeks)
return d + delta
I have slightly modified the script of Vaidas K. in a way that it will return the beginning of the week and the end day of the week.
from datetime import datetime, date, timedelta
def weekbegend(year, week):
"""
Calcul du premier et du dernier jour de la semaine ISO
"""
d = date(year, 1, 1)
delta_days = d.isoweekday() - 1
delta_weeks = week
if year == d.isocalendar()[0]:
delta_weeks -= 1
# delta for the beginning of the week
delta = timedelta(days=-delta_days, weeks=delta_weeks)
weekbeg = d + delta
# delta2 for the end of the week
delta2 = timedelta(days=6-delta_days, weeks=delta_weeks)
weekend = d + delta2
return weekbeg, weekend
Soyou can use it that way.
weekbeg, weekend = weekbegend(2009, 1)
begweek = weekbeg.strftime("%A %d %B %Y")
endweek = weekend.strftime("%A %d %B %Y")
from datetime import date, timedelta
def first_monday(year, week):
d = date(year, 1, 4) # The Jan 4th must be in week 1 according to ISO
return d + timedelta(weeks=(week-1), days=-d.weekday())
If I have a certain week number (eg 51) and a given year (eg 2008), how do I find the date of the first Monday of that same week?
Many thanks
>>> import time
>>> time.asctime(time.strptime('2008 50 1', '%Y %W %w'))
'Mon Dec 15 00:00:00 2008'
Assuming the first day of your week is Monday, use %U instead of %W if the first day of your week is Sunday. See the documentation for strptime for details.
Update: Fixed week number. The %W directive is 0-based so week 51 would be entered as 50, not 51.
This seems to work, assuming week one can have a Monday falling on a day in the last year.
from datetime import date, timedelta
def get_first_dow(year, week):
d = date(year, 1, 1)
d = d - timedelta(d.weekday())
dlt = timedelta(days = (week - 1) * 7)
return d + dlt
Use the string formatting found in the time module. Detailed explanation of the formats used
>>> import time
>>> time.strptime("51 08 1","%U %y %w")
(2008, 12, 22, 0, 0, 0, 0, 357, -1)
The date returned is off by one week according to the calendar on my computer, maybe that is because weeks are indexed from 0?
PEZ’s and Gerald Kaszuba’s solutions work under assumption that January 1st will always be in the first week of a given year. This assumption is not correct for ISO calendar, see Python’s docs for reference. For example, in ISO calendar, week 1 of 2010 actually starts on Jan 4, and Jan 1 of 2010 is in week 53 of 2009. An ISO calendar-compatible solution:
from datetime import date, timedelta
def week_start_date(year, week):
d = date(year, 1, 1)
delta_days = d.isoweekday() - 1
delta_weeks = week
if year == d.isocalendar()[0]:
delta_weeks -= 1
delta = timedelta(days=-delta_days, weeks=delta_weeks)
return d + delta
I have slightly modified the script of Vaidas K. in a way that it will return the beginning of the week and the end day of the week.
from datetime import datetime, date, timedelta
def weekbegend(year, week):
"""
Calcul du premier et du dernier jour de la semaine ISO
"""
d = date(year, 1, 1)
delta_days = d.isoweekday() - 1
delta_weeks = week
if year == d.isocalendar()[0]:
delta_weeks -= 1
# delta for the beginning of the week
delta = timedelta(days=-delta_days, weeks=delta_weeks)
weekbeg = d + delta
# delta2 for the end of the week
delta2 = timedelta(days=6-delta_days, weeks=delta_weeks)
weekend = d + delta2
return weekbeg, weekend
Soyou can use it that way.
weekbeg, weekend = weekbegend(2009, 1)
begweek = weekbeg.strftime("%A %d %B %Y")
endweek = weekend.strftime("%A %d %B %Y")
from datetime import date, timedelta
def first_monday(year, week):
d = date(year, 1, 4) # The Jan 4th must be in week 1 according to ISO
return d + timedelta(weeks=(week-1), days=-d.weekday())