Wrap-up

Working with Dates and Times in Python

Max Shron

Data Scientist and Author

Recap: Dates and Calendars

The date() class takes a year, month, and day as arguments
A date object has accessors like .year, and also methods like .weekday()
date objects can be compared like numbers, using min(), max(), and sort()
You can subtract one date from another to get a timedelta
To turn date objects into strings, use the .isoformat() or .strftime() methods

The datetime() class takes all the arguments of date(), plus an hour, minute, second, and microsecond
All of the additional arguments are optional; otherwise, they're set to zero by default
You can replace any value in a datetime with the .replace() method
Convert a timedelta into an integer with its .total_seconds() method
Turn strings into dates with .strptime() and dates into strings with .strftime()

A datetime is "timezone aware" when it has its tzinfo set. Otherwise it is "timezone naive"
Setting a timezone tells a datetime how to align itself to UTC, the universal time standard
Use the .replace() method to change the timezone of a datetime, leaving the date and time the same
Use the .astimezone() method to shift the date and time to match the new timezone
dateutil.tz provides a comprehensive, updated timezone database

When reading a csv, set the parse_dates argument to be the list of columns which should be parsed as datetimes
If setting parse_dates doesn't work, use the pd.to_datetime() function
Grouping rows with .groupby() lets you calculate aggregates per group. For example, .first(), .min() or .mean()
.resample() groups rows on the basis of a datetime column, by year, month, day, and so on
Use .tz_localize() to set a timezone, keeping the date and time the same
Use .tz_convert() to change the date and time to match a new timezone

Working with Dates and Times in Python