94 – Dynamic width string formatting

String formatting accepts formatting specifiers dynamically if you specify them within an extra set of curly braces {}. This is useful, for example, to compute the maximum width of a column from a list of strings to format them neatly:

fruits = ["banana", "cantalope", "pear"]
max_width = max(map(len, fruits))
# max_width is 9

for idx, fruit in enumerate(fruits, start=1):
    print(f"{fruit:<{max_width}} - {idx}")
#                   ^^^^^^^^^^^

banana    - 1
cantalope - 2
pear      - 3

Note how all fruits are left aligned on a field that is as wide as the word “cantalope”, since the variable max_width has the value 9. To tell the string formatting that the width is supposed to be the value of the variable max_width, you specify the width as {max_width} inside the format.