Use f-strings instead of .format()

[Viicos]

Using pyupgrade with the following command:

pyupgrade --py37-plus  `find . -name "*.py"`

• Converted .format to f-strings
• Simplify is_async_available in utils.py

You might want to keep .format in some places, as it could be easier to read

note: pyupgrade is intentionally timid and will not create an f-string if it would make the expression longer or if the substitution parameters are sufficiently complicated (as this can decrease readability).

[adamjmcgrath]

Thanks @Viicos