You might have noticed that the date class doesn't have properties for hours, minutes and seconds. And the time class doesn't have properties for year, month and day.
This is great: concerns are nicely separated, each class does exactly what it needs to do, no more no less, I don't have to create objects more comples than I actually need and so on. But what if I need to represent, say, the time and date of an event, years to milliseconds?
If I want to represent the exact moment of my birth, I need to store both the date and the time. Do I need to use two separate objects for this? If I want to know how many seconds passed from my birth up until now, do I need four objects? Do I need to write all the code to do that?
Fear not, since the datetime module has a datetime class to do this and more.
To create a datetime object you have several options. You can use the contructor:
my_birthdate = datetime(year, month, day[, hour[, minute[, second[, microsecond[, tzinfo]]]]])
It takes many arguments, but only year, month and day are mandatory. Since datetime is a date composed with a time object, the meaning is exactly the same you saw the past weeks.
You can also build an object from a UNIX timestamp (number of seconds since 1/1/1970) using:
my_birthdate = datetime.fromtimestamp(timestamp[, tz])
As usual, the timezone is optional. You can use an "ordinal", that is the number of days since day one of year one:
my_birthdate = datetime.fromordinal(ordinal)
For example, today is:
>>> import datetime
>>> datetime.datetime.now().toordinal()
735072
As you might have guessed, datetime.now() creates an object representing the date and time of the exact moment when the method gets called, and toordinal() converts it to ordinal. Note that this way you are actually only representing the date, not the time.
If you have a formatted string representing date and time, you can create an object using:
my_birthdate = datetime.strptime(date_string, format_string)
where you have to pass both the date and time string, and the format string, which is the same you would pass to the strftime you saw in the date review.
Last but not least, if you already have a date and a time object and just want to stick them together, then use the combine method:
my_birthdate = datetime.combine(date, time)
This variety of factory and constructor methods allows you a great degree of freedom and flexibility in the development of your application. You can represent dates and times using whatever convention suits you best: Python has a method for that!
Next time we'll see what we can do with these objects, but since I'd hate to leave you with a dry mouth, I'll guide you through a simple example in the problem of the week.
So, let's say you actually want to know how many seconds passed from your birth up until now. The docs page has everything you need to do it, but it involves methods and classes that haven't been covered yet in our reviews. So, I've prepared a Gist to assist you in the task.
https://gist.github.com/nofatclips/6061651
Good luck