[FIXED] How to setup rounding halves to down in f-string format?

Issue

I'm trying to change the behaviour of my code in this way, expected behaviour:

2249 -> 2.2
2250 -> 2.2
2251 -> 2.3
2349 -> 2.3
2350 -> 2.3
2351 -> 2.4

But f'{num:.3g}' rounds it differently:

from decimal import *
def format_number(num):
  getcontext().prec = 1
  getcontext().rounding = ROUND_HALF_DOWN

  num = Decimal(num)
  print(num)
  num = float(f'{num:.3g}')
  print(num)
  magnitude = 0
  while abs(num) >= 1000:
    magnitude += 1
    num /= 1000.
  num = round(num * 10.) / 10.
  return f"{f'{num:f}'.rstrip('0').rstrip('.')}{['', 'k', 'M', 'B', 'T'][magnitude]}"

format_number(2349)
2349
2350.0
'2.4k'

How can I change it and keep "thouthands to letter" replacement?

Solution

You can change the precision width of your format of num as 2 instead of 3. that will round the digits after the precision width. since you only seem to want precision of the first two digits it will round these using the remaining digits.

from decimal import *


def format_number(num):
    getcontext().prec = 1
    getcontext().rounding = ROUND_HALF_DOWN

    num = Decimal(num)
    #print(num)
    num = float(f'{num:.2g}')
    #print(num)
    magnitude = 0
    while abs(num) >= 1000:
        magnitude += 1
        num /= 1000.
    num = round(num * 10.) / 10.
    return f"{f'{num:f}'.rstrip('0').rstrip('.')}{['', 'k', 'M', 'B', 'T'][magnitude]}"


nums = [2249, 2250, 2251, 2349, 2350, 2351, 2349345, 2351345]
for num in nums:
    print(f"{num} -> {format_number(num)}")

OUTPUT

2249 -> 2.2k
2250 -> 2.2k
2251 -> 2.3k
2349 -> 2.3k
2350 -> 2.3k
2351 -> 2.4k
2349345 -> 2.3M
2351345 -> 2.4M

Answered By - Chris Doyle

Answer Checked By - Terry (PHPFixing Volunteer)