Python-string formatting with variable length

Question

I'm trying to pad dynamic elements within a table, but it seems as though the native padding function doesn't work with variables. Just wondering if I'm doing something wrong or if there are simple alternatives to center padding. I know of ljust and rjust but there is no m(iddle)just for some reason.

Simple example:

a=10
b='hi'
print(f'{b:^a}')

or

a=10
b='hi'
print('{:^a}'.format(b))

produces

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: Unknown format code 'a' for object of type 'str'

Typing 10 in place of a in the print statement makes it work as intended, so I'm guessing 'a' is being interpreted as a string by the string formatted. Is a helper function the only way out here?

Answer 1

In [114]: print(f'{b:^{a}}')                                                                                                                                                                                                                                                 
    hi    

In [115]: print(f'"{b:^{a}}"')                                                                                                                                                                                                                                               
"    hi    "