How to format a decimal in python with variable number of decimals

Question

To format the number 20 as 20.00 I can do:

'%.2f' % 20.283928
'20.28'

However, I want to allow the user to be able to specify the number of decimal places. For example:

value = 20.283928
num_decimal_places = 7 # from user input
'%.%sf' % (20, '7')

How could I do something like the above?

Answer 1

If version of python greater or equals to 3.6:

print(f'%.{num_decimal_places}f'%value)

Output:

20.2839280

Answer 2

If you are willing to use newer format you can do this:

>>> n = 4
>>> value = 20.283928
>>> '{:.{count}f}'.format(value, count=n)

'20.2839'