How to use self-docummenting equals (debugging) specifier with str.format()?

Question

Python 3.8 introduced = specifier in f-strings (see this issue and pull request).

It allows to quickly represent both the value and the name of the variable:

from math import pi as π
f'{π=}'
# 'π=3.141592653589793'

I would like to use this feature on a pre-defined string with str.format():

'{π=}'.format(π=π)

However, it raises an exception:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
KeyError: 'π='

Is there a way to make it work (e.g. with a special dunder method)?

Why it may be useful?

• one could have a programmatic template for multiple values of the same variable (in a loop)
  • in contrasts, f-strings have to be hardcoded; think about internationalization
• one could reference constants defined in a module in its docstring (module.__doc__.format(**vars(module));
  • workaround: define an f-string variable at the end of the module, overwrite the module.__doc__ at runtime.