The tab is working properly, you probably are looking for .ljust(width)

lems = ['scaena', 'persona', 'improbus']
for i in lems:
    print('{}{}'.format(i.ljust(10), 'whatever'))

prints out:

scaena    whatever
persona   whatever
improbus  whatever

Sometimes it's useful to calculate the max length of your strings so the output is more reliable

lems = ['scaena', 'persona', 'improbus']
max_len = max(len(l) for l in lems)
for i in lems:
    print('{}{}'.format(i.ljust(max_len + 1), 'whatever'))

This might be what you want.

>>> test_str = '''
... list {}
... list
...     {}
... '''
>>> values
['1', '2', '3']
>>> print(test_str.format(','.join(values), ',\n\t'.join(values)))

list 1,2,3
list
    1,
    2,
    3

Addendum:

Notice that the function creates the string that it returns in the form of a new-fangled f string, thus allowing the possibility of substitution of the values returned by functions or other expressions within it.

>>> def a_string(v1, v2):
...     def f1(val):
...         return '---'+val
...     def f2(val):
...         return '+++'+val
...     return f'''{f1(v1)} is bigger than {f2(v2)}'''
... 
>>> a_string('2', '1')
'---2 is bigger than +++1'