Python has always had a “batteries included” philosophy - having a rich and versatile standard library which is immediately available, without making the user download separate packages. This is thought to have contributed to Python’s early success. No matter what you’re trying to accomplish, there’s probably a built-in library that can help you do what you want.
The downside to this is that the standard libraries need to maintain backwards compatibility. Some were quick hacks, hard to use, poorly designed and now impossible to fix, or have simply been rendered obsolete. Luckily, Python also makes it easy to install and use external libraries - we’ll cover this later.
There are some great libraries included with Python that you’ll probably end up seeing or using frequently. sys provides system-specific parameters and functions, such as exit(). os has miscellaneous operating system interfaces, and provides the excellent os.path submodule for handling file paths on any operating system. math gives you all the advanced math function. json is an easy-to-use json parser and encoder. Python even gives you built-in libraries for database access, logging, internet protocols, multimedia, debugging, and even libraries for extending Python itself. The full list of standard libraries can be found in the Python documentation.
As a quick example, let’s look at Python’s datetime library. You can easily make a datetime object that represents any given point in time. For example:
>>> import datetime
>>> right_now = datetime.datetime.now()
>>> print(right_now)
2019-03-17 13:41:10.994700
>>> repr(right_now)
'datetime.datetime(2019, 3, 17, 13, 41, 10, 994700)'
We can even make a datetime object for an arbitrary date, and subtract it from right now to get a timedelta object:
>>> new_years = datetime.datetime(2019, 1, 1, 0, 0)
>>> print(new_years)
2019-01-01 00:00:00
>>> delta = right_now - new_years
>>> print(delta)
75 days, 13:41:10.994700
We can easily see that it’s been over 75 days from new_years until right_now. We’ll come back to datetime later in this chapter.