Function format_pretty_dec 

pub fn format_pretty_dec<N: Num + Display + 'static>(num: N) -> String

Pretty print integer and float numbers with base 10, separated by underscores grouping the digits in threes

use parse_int::format_pretty_dec;
assert_eq!("12_345.678_9", format_pretty_dec(12345.6789));
assert_eq!("12_345", format_pretty_dec(12345));