Python – How to format a floating number to fixed width in Python

number-formattingnumberspythonstring

How do I format a floating number to a fixed width with the following requirements:

  1. Leading zero if n < 1
  2. Add trailing decimal zero(s) to fill up fixed width
  3. Truncate decimal digits past fixed width
  4. Align all decimal points

For example:

% formatter something like '{:06}'
numbers = [23.23, 0.123334987, 1, 4.223, 9887.2]

for number in numbers:
    print formatter.format(number)

The output would be like

  23.2300
   0.1233
   1.0000
   4.2230
9887.2000

Best Answer

numbers = [23.23, 0.1233, 1.0, 4.223, 9887.2]                                                                                                                                                   
                                                                                                                                                                                                
for x in numbers:                                                                                                                                                                               
    print("{:10.4f}".format(x))

prints

   23.2300
    0.1233
    1.0000
    4.2230
 9887.2000

The format specifier inside the curly braces follows the Python format string syntax. Specifically, in this case, it consists of the following parts:

  • The empty string before the colon means "take the next provided argument to format()" – in this case the x as the only argument.
  • The 10.4f part after the colon is the format specification.
  • The f denotes fixed-point notation.
  • The 10 is the total width of the field being printed, lefted-padded by spaces.
  • The 4 is the number of digits after the decimal point.
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