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Building Robust Object-Oriented Python Applications and Libraries

Custom Formatters

Explore how to apply Python's custom string formatting capabilities using the format() method and f-strings. Understand how to use positional and named placeholders in templates and consider extending formatting via overriding __format__. This lesson helps you manipulate strings effectively in applications.

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Overview

While these standard formatters apply to most built-in objects, it is also possible for other objects to define nonstandard specifiers. For example, if we pass a datetime object into format, we can use the specifiers used in the datetime.strftime() function, as follows:

Python 3.10.4
import datetime
important = datetime.datetime(2019, 10, 26, 13, 14)
formatted_date = f"{important:%Y-%m-%d %I:%M%p}"
print(formatted_date)

It is even possible to write custom formatters for objects we create ourselves, but that is beyond the scope of this book. Look into overriding the __format__() special method if we need to do this in our code.

The Python formatting syntax is quite flexible, ...