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datetime ​

The datetime module is the standard library for handling dates and times in Python.

Getting Current Date and Time ​

To obtain the current date and time:

python
from datetime import datetime
now = datetime.now()  # Get current datetime
print(now)
print(type(now))  # <class 'datetime.datetime'>

datetime is both a module and a class within that module. If you import it directly, you access the class.

Specifying a Date and Time ​

You can create a datetime object using specific parameters:

python
dt = datetime(2015, 4, 19, 12, 20)  # Create datetime with specified date and time
print(dt)  # 2015-04-19 12:20:00

Converting datetime to Timestamp ​

To convert a datetime object to a timestamp, use the timestamp() method:

python
timestamp = dt.timestamp()  # Convert datetime to timestamp
print(timestamp)  # 1429417200.0

Converting Timestamp to datetime ​

To convert a timestamp back to a datetime object:

python
t = 1429417200.0
print(datetime.fromtimestamp(t))  # Local time
print(datetime.utcfromtimestamp(t))  # UTC time

Converting String to datetime ​

To convert a string representation of date and time into a datetime object:

python
cday = datetime.strptime('2015-6-1 18:19:59', '%Y-%m-%d %H:%M:%S')
print(cday)  # 2015-06-01 18:19:59

Converting datetime to String ​

To format a datetime object as a string:

python
now = datetime.now()
print(now.strftime('%a, %b %d %H:%M'))  # Mon, May 05 16:28

datetime Arithmetic ​

You can perform arithmetic operations on datetime using the timedelta class:

python
from datetime import timedelta
now + timedelta(hours=10)  # Add 10 hours
now - timedelta(days=1)  # Subtract 1 day

Local Time to UTC Time ​

You can assign a timezone to a datetime object using the timezone class:

python
from datetime import timezone
tz_utc_8 = timezone(timedelta(hours=8))
dt = now.replace(tzinfo=tz_utc_8)

Timezone Conversion ​

To convert between timezones, you can use astimezone():

python
utc_dt = datetime.utcnow().replace(tzinfo=timezone.utc)
bj_dt = utc_dt.astimezone(timezone(timedelta(hours=8)))  # Beijing time
tokyo_dt = utc_dt.astimezone(timezone(timedelta(hours=9)))  # Tokyo time

Summary ​

datetime requires timezone information for specific time representation. It’s best to store datetime as a timestamp, which is timezone-independent.

Exercise ​

Create a function to convert user-input date and time with timezone information into a timestamp:

python
def to_timestamp(dt_str, tz_str):
    pass

# Test:
t1 = to_timestamp('2015-6-1 08:10:30', 'UTC+7:00')
assert t1 == 1433121030.0, t1

t2 = to_timestamp('2015-5-31 16:10:30', 'UTC-09:00')
assert t2 == 1433121030.0, t2

print('ok')