Given this code:

print(f"Here is that pesky {xxx/2:.3f} again")

The traceback prints:

Traceback (most recent call last):
  File "/home/pablogsal/github/python/main/lel.py", line 1, in <module>
    print(f"Here is that pesky {xxx/2:.3f} again")
           ^^^
NameError: name 'xxx' is not defined

Removing the formatting part ":.3f" makes it work as expected