dtpy

Question 1

naive datetimes do not know

Answer 1

what timezone they are in

Question 2

aware datetimes know

Answer 2

what timezone you are in

Question 3

to create a naive date, type

Answer 3

datetime.date(2000, 12, 30)

Question 4

you should not use a local time zone in apps for anything except

Answer 4

converting it to display for users.

Question 5

datetime.datetime.now(), datetime.time.now(), datetime.date.now() return the time/date in

Answer 5

my local timezone from computer, but in a naive form.

Question 6

to return the day of week in 0-6 format, type

Answer 6

my_datetime.weekday()

Question 7

a timedelta represents

Answer 7

the amount of time between 2 dates or times

Question 8

to create a timedelta of 7 days type

Answer 8

datetime.timedelta(days=7)

Question 9

to print out what the date will be in 7 days, type

Answer 9

datetime.date().today() + datetime.timedelta(days=7)

Question 10

if you subtract a date or time from a date or time you get a

Answer 10

timedelta

note: cannot add

Question 11

to return the number of seconds of a timedelta, type

Answer 11

my_time_delta.total_seconds()

Question 12

the parameters to datetime.time() are

Answer 12

hours, minutes, seconds, milliseconds.

Question 13

to get the current datetime in utc

Answer 13

datetime. datetime.now(tz= pytz.UTC)

note: Yes, this gets the time local to there, not my local timeand then just setting UTC as timezone.

Question 14

to make an aware datetime, type

Answer 14

datetime.datetime(2016,10,20, 20, 10, 20000, tzinfo = pytz.UTC)

Question 15

to convert a timezone aware datetime to the concurrent local time in a different timezone, type

Like at this time here, whats the local time there?

Answer 15

my_datetime.astimezone(pytz.timezone(‘TIMEZONE/STRING’))

Question 16

To know when a datetime is timezone aware, you can

Answer 16

return it and see tzinfo
datetime.datetime(2018, 12, 25, 4, 15, 24, 686585, tzinfo=)

or print it and see the plus
2019-10-20 11-25-20.304943+08:00

Question 17

an unaware datetime is effectively just

Answer 17

the numbers that make up all the date and time, but they don’t know what timezone they are in.

If you add a timezone, you get to know the time difference a datetime that knows what timezone it is in, and one that doesnt. If it is in a different timezone, it can account for the timezone difference to know the actually difference. Since there 6pm ET and 6pm PT look the same in numbers, but 6pm PT will happen in the future after 6pm ET.

Question 18

to make a naive datetime into a timezone aware datetime, type

Answer 18

from pytz import timezone

unaware_datetime = datetime.datetime.now()

time_zone = timezone(‘TIMEZONE/STRING’)

aware_datetime = time_zone.localize(unaware_datetime)

Question 19

to convert a datetime to a string, type

Answer 19

my_datetime.strftime(‘%b %d %Y’)

returnstringf -> RSF

https://www.youtube.com/watch?v=eirjjyP2qcQ

Question 20

to convert a string to a datetime, type

Answer 20

datetime.datetime.strptime(“string”, “%b %d %Y”)

returndatetimep -> RDP

Question 21

to convert a timezone aware datetime into a naive datetime, type

Answer 21

aware_datetime.replace(tzinfo=None)

Question 22

to get the timedelta between to times, you need to

Answer 22

put those times into a datetime with the same date first

the bigger later/bigger date must come first to subtract

Question 23

to convert a naive datetime to a timezone aware datetime using the timezone in django’s settings, type

Answer 23

from django.utils.timezone import make_aware

make_aware(naive_datetime)

Question 24

auto_now_add is

Answer 24

timezone aware

Question 25

timedeltas can be

Answer 25

negative

Question 26

to get a datetime representing the monday in a given week, type

Answer 26

datetime.datetime.strptime('2000-07-3', '%Y-%W-%w') ``` %W = week number zero padded %w = day of week 0-6 ```

Question 27

To replace just the time in a datetime, type

Answer 27

datetime.datetime.utcnow().replace(tzinfo= pytz.UTC, hour= 3, minute= 0, second= 0)

Question 28

when I make pivot tables in pandas, I need to always catch

Answer 28

coonditions where there is no data, so I need to render an empty dataframe

Question 29

general dango_pandas rules

Answer 29

after you read_frame, create a new df filtering for just the columns need so model changes don't later change the df To make a pivot table with cell links, include all the links as later columns of the pivot table, and then in template loop using iterrows. Make the df look exactly how you want it to be displayed, dont rely on template a lot, but template filters are ok. Account for the possibility that your data will be empty, make sure table still populates keep in the template to see the real data

Question 30

when filtering for a particular date range in django make sure to use

Answer 30

__gte and __lte instead of just gt or lt, because you need to include the date that set the range.

Question 31

to get the first monday of every week, type

Answer 31

``` def get_monday(year, week): d = datetime.date(year,1,1) if(d.weekday()>3): d = d+datetime.timedelta(7-d.weekday()) else: d = d - datetime.timedelta(d.weekday()) dlt = datetime.timedelta(days = (week-1)*7) return d + dlt ```

Question 32

datetime.date.isocalendar() returns

Answer 32

a tuple containing year, weeknumber and weekday

Question 33

to get the current datetime in a chosen timezone, type

Answer 33

datetime. datetime.now(pytz.timezone('US/Eastern')) | note: this is tz aware