ArielAlon24 / typelate

Python templates with type annotations and validation.

typelate

Python templates with type annotations and validation.

Background

A somewhat hidden feature in Python is the ability to create str templates, they are similar to f-strings but they don't require you to know the values in advance.

template = "Hello, {name}!"

Using it is as simple as calling the format function

>>> template.format(name="World")
"Hello, World!"

>>> template.format(name=123)
"Hello, 123!"

In addition to that, like f-strings we can specify a format specifier to each argument.

template = "Pi is {pi: .2f}"

>>> import math
>>> template.format(pi=math.pi)
"Pi is 3.14"

Usage

With typelate this behavior is extended even more, now you can specify types for each argument in the template, in runtime a template formatting will have validation that can be handled as you wish!

from typelate import Template

template = Template("Hello, {name: str}!")

Notice that Template uses the __call__ instead of format

>>> template(name="World")
"Hello, World!"

Now, let's pass an invalid type.

>>> template(name=123)
TypeError: Incorrect type for replacement 'name', expected: <class 'str'>.

Moreover, you can use the default format specifiers in addition to the type annotation:

from typelate import Template

template = Template("Pi is {pi: float: .2f}")

>>> import math
>>> template(pi=math.pi)
"Pi is 3.14"