How to print binary numbers using f"" string instead of .format()?

Here is my take:

In the old .format() the 0 represented the 1st element passed to the format function. "{0:>2} in binary is {0:>08b}".format(i). 0 was used twice to access the first variable twice. Another way of writing it would be: "{:>2} in binary is {:>08b}".format(i,i) omitting the indices.

In the new f'' format we pass variables/expressions instead.

Your f-string should have expressions in it rather than indices:

f'{i:>2} in binary is {i:>08b}'

Anywhere you had 0 in the original format string should be replaced by the actual first argument: in this case i.

Caveat

The expression in the f-string is evaluated twice, but the argument to format is only evaluated once when you access it by index. This matters for more complicated expressions. For example:

"{0:>2} in binary is {0:>08b}".format(i + 10)

Here the addition i + 10 only happens once. On the other hand

f"{i+10:>2} in binary is {i+10:>08b}"

does the addition twice because it is equivalent to

"{:>2} in binary is {:>08b}".format(i + 10, i + 10)

Or

"{0:>2} in binary is {1:>08b}".format(i + 10, i + 10)

The workaround is to pre-compute the results of expressions that appear in your f-string more than once:

j = i + 10
f"{j:>2} in binary is {j:>08b}"

Now j is evaluated multiple times, but it's just a simple reference.