# Exercises¶

It is often useful to work through some examples in order to understand how a module works; on this page, there are several exercises of varying difficulty that you can use to learn how to use `dateutil`.

If you are interested in helping improve the documentation of `dateutil`, it is recommended that you attempt to complete these exercises with no resources other than dateutil’s documentation. If you find that the documentation is not clear enough to allow you to complete these exercises, open an issue on the dateutil issue tracker to let the developers know what part of the documentation needs improvement.

## Martin Luther King Day¶

Martin Luther King, Jr Day is a US holiday that occurs every year on the third Monday in January?

How would you generate a recurrence rule that generates Martin Luther King Day, starting from its first observance in 1986?

Test Script

To solve this exercise, copy-paste this script into a document, change anything between the `--- YOUR CODE ---` comment blocks.

```# ------- YOUR CODE -------------#
from dateutil import rrule

# -------------------------------#

from datetime import datetime
MLK_TEST_CASES = [
((datetime(1970, 1, 1), datetime(1980, 1, 1)),
[]),
((datetime(1980, 1, 1), datetime(1989, 1, 1)),
[datetime(1986, 1, 20),
datetime(1987, 1, 19),
datetime(1988, 1, 18)]),
((datetime(2017, 2, 1), datetime(2022, 2, 1)),
[datetime(2018, 1, 15, 0, 0),
datetime(2019, 1, 21, 0, 0),
datetime(2020, 1, 20, 0, 0),
datetime(2021, 1, 18, 0, 0),
datetime(2022, 1, 17, 0, 0)]
),
]

def test_mlk_day():
for (between_args, expected) in MLK_TEST_CASES:
assert MLK_DAY.between(*between_args) == expected

if __name__ == "__main__":
test_mlk_day()
print('Success!')
```

A solution to this problem is provided here.

## Next Monday meeting¶

A team has a meeting at 10 AM every Monday and wants a function that tells them, given a `datetime.datetime` object, what is the date and time of the next Monday meeting? This is probably best accomplished using a relativedelta.

Test Script

To solve this exercise, copy-paste this script into a document, change anything between the `--- YOUR CODE ---` comment blocks.

```# --------- YOUR CODE -------------- #
from dateutil import relativedelta

def next_monday(dt):

# ---------------------------------- #

from datetime import datetime
from dateutil import tz

NEXT_MONDAY_CASES = [
(datetime(2018, 4, 11, 14, 30, 15, 123456),
datetime(2018, 4, 16, 10, 0)),
(datetime(2018, 4, 16, 10, 0),
datetime(2018, 4, 16, 10, 0)),
(datetime(2018, 4, 16, 10, 30),
datetime(2018, 4, 23, 10, 0)),
(datetime(2018, 4, 14, 9, 30, tzinfo=tz.gettz('America/New_York')),
datetime(2018, 4, 16, 10, 0, tzinfo=tz.gettz('America/New_York'))),
]

def test_next_monday_1():
for dt_in, dt_out in NEXT_MONDAY_CASES:
assert next_monday(dt_in) == dt_out

if __name__ == "__main__":
test_next_monday_1()
print('Success!')
```

## Parsing a local tzname¶

Three-character time zone abbreviations are not unique in that they do not explicitly map to a time zone. A list of time zone abbreviations in use can be found here. This means that parsing a datetime string such as `'2018-01-01 12:30:30 CST'` is ambiguous without context. Using dateutil.parser and dateutil.tz, it is possible to provide a context such that these local names are converted to proper time zones.

### Problem 1¶

Given the context that you will only be parsing dates coming from the continental United States, India and Japan, write a function that parses a datetime string and returns a timezone-aware `datetime` with an IANA-style timezone attached.

Note: For the purposes of the experiment, you may ignore the portions of the United States like Arizona and parts of Indiana that do not observe daylight saving time.

Test Script

To solve this exercise, copy-paste this script into a document, change anything between the `--- YOUR CODE ---` comment blocks.

```# --------- YOUR CODE -------------- #
from dateutil.parser import parse
from dateutil import tz

def parse_func_us_jp_ind():

# ---------------------------------- #

from dateutil import tz
from datetime import datetime

PARSE_TZ_TEST_DATETIMES = [
datetime(2018, 1, 1, 12, 0),
datetime(2018, 3, 20, 2, 0),
datetime(2018, 5, 12, 3, 30),
datetime(2014, 9, 1, 23)
]

PARSE_TZ_TEST_ZONES = [
tz.gettz('America/New_York'),
tz.gettz('America/Chicago'),
tz.gettz('America/Denver'),
tz.gettz('America/Los_Angeles'),
tz.gettz('Asia/Kolkata'),
tz.gettz('Asia/Tokyo'),
]

def test_parse():
for tzi in PARSE_TZ_TEST_ZONES:
for dt in PARSE_TZ_TEST_DATETIMES:
dt_exp = dt.replace(tzinfo=tzi)
dtstr = dt_exp.strftime('%Y-%m-%d %H:%M:%S %Z')

dt_act = parse_func_us_jp_ind(dtstr)
assert dt_act == dt_exp
assert dt_act.tzinfo is dt_exp.tzinfo

if __name__ == "__main__":
test_parse()
print('Success!')
```

### Problem 2¶

Given the context that you will only be passed dates from India or Ireland, write a function that correctly parses all unambiguous time zone strings to aware datetimes localized to the correct IANA zone, and for ambiguous time zone strings default to India.

Test Script

To solve this exercise, copy-paste this script into a document, change anything between the `--- YOUR CODE ---` comment blocks.

```# --------- YOUR CODE -------------- #
from dateutil.parser import parse
from dateutil import tz

def parse_func_ind_ire():

# ---------------------------------- #
ISRAEL = tz.gettz('Asia/Jerusalem')
INDIA = tz.gettz('Asia/Kolkata')
PARSE_IXT_TEST_CASE = [
('2018-02-03 12:00 IST+02:00', datetime(2018, 2, 3, 12, tzinfo=ISRAEL)),
('2018-06-14 12:00 IDT+03:00', datetime(2018, 6, 14, 12, tzinfo=ISRAEL)),
('2018-06-14 12:00 IST', datetime(2018, 6, 14, 12, tzinfo=INDIA)),
('2018-06-14 12:00 IST+05:30', datetime(2018, 6, 14, 12, tzinfo=INDIA)),
('2018-02-03 12:00 IST', datetime(2018, 2, 3, 12, tzinfo=INDIA)),
]

def test_parse_ixt():
for dtstr, dt_exp in PARSE_IXT_TEST_CASE:
dt_act = parse_func_ind_ire(dtstr)
assert dt_act == dt_exp, (dt_act, dt_exp)
assert dt_act.tzinfo is dt_exp.tzinfo, (dt_act, dt_exp)

if __name__ == "__main__":
test_parse_ixt()
print('Success!')
```