Reduce decimals shown for large numbers but not for small

Question

When formatting floats, is there any python method/formatting for reducing how many decimals that is shown as the number becomes larger?

It could for instance be a limit to how many digits of the number that is shown. Example below:

 100.145 ->  100
   2.392 ->    2.39
  34.827 ->   34.8
4599.298 -> 4599

Answer 1

Update:

As chux points out in his comment, my original solution does not work for boundary cases in which rounding leads to a carry. Also, I didn't pay attention to the fact that log10(100) == 2 != 3. The second bug is easy to come by. To fix the first one, I came up with a recursion. Now it should work but isn't simple anymore.

import math

def flexible_format(num_in, total_digits):
    try:
        digits_before_decimal = math.floor(math.log10(abs(num_in))) + 1
    except ValueError:
        # if num == 0
        return '0'
    digits_after_decimal = max(0, total_digits - digits_before_decimal)
    # if rounding increases number of digits, we have to format once again
    # after that, an additional rounding doesn't increase the number of digits
    # so we can be sure not to land in an infinite recursion 
    num_out = round(num_in, digits_after_decimal)
    if math.floor(math.log10(abs(num_out))) >= digits_before_decimal:
        return flexible_format(num_out, total_digits)
    return f'{num_out:.{digits_after_decimal}f}'

list_nums =  [-100.145,  2.392, -34.827 , 4599.298, 99.95, 100 ]
for num in list_nums:
    print(flexible_format(num, total_digits=3))
 
# -100
# 2.39
# -34.8
# 4599
# 100
# 100

Original false solution:

I don't know a commonly used function achieving that, but it is easy to implement.

import math

def flexible_format(num, total_digits):
    try:
        digits_before_decimal = math.ceil(math.log10(abs(num)))
    except ValueError:
        # if num == 0
        return '0'
    digits_after_decimal = max(0, total_digits - digits_before_decimal)
    return f'{num:.{digits_after_decimal}f}'

list_nums =  [-100.145,  2.392, -34.827 , 4599.298, 0]

for num in list_nums:
    print(flexible_format(num, total_digits=3))

# -100
# 2.39
# -34.8
# 4599
# 0