UPDATED ANSWER:

You can compose multiple format specifiers. Below, +.1f is used to keep the sign, and print to only 1 decimal place. and <10 is used to justify the string.

values = [-1.0, 2.2]

for value in values:
    print(f"someLjustedStrings{value:<+10.1f}someLjustedStrings")

OLD ANSWER:

You can try this:

values = [-1.0, 2.2]

for value in values:
    print(f"someLjustedStrings{['+', '-'][value<0]}{abs(value):<10}someLjustedStrings")

Output:

someLjustedStrings-1.0       someLjustedStrings
someLjustedStrings+2.2       someLjustedStrings

< followed by int for ljust

> followed by int for rjust

EDIT:

If you want to ljust by variable:

LJUST = {'value': 10}
values = [-1.0, 2.2]

for value in values:
    print(f"someLjustedStrings{['+', '-'][value<0]}{abs(value):<{LJUST['value']}}someLjustedStrings")

Output:

someLjustedStrings-1.0       someLjustedStrings
someLjustedStrings+2.2       someLjustedStrings