Format number to at most n digits in python

Question

I know I can use format in order to format a number to whatever format. What I want is to format to at most n digts.

This can be achieved using the g-format-specifier. But there's one caveat here. What if my input is a really small number, e.g. -0.0000000001. With g this prints as -1e-10, but I want it to return simply 0.

I tried to do format(round(mynumber, 7)), but that interestingly gave me -0 (with a leading -) when mynumber is negative near zero.

How can I format mynumber to at most 7 digits without a leading sign, if the number is near zero?

Afterall this is my input and the expected result:

-0.0000000001 -> 0
 0.0000000001 -> 0
 3            -> 3
 3.1415927    -> 3.1415927

I got the output: 1e-07 when input is -0.0000000001. Is that Okay or not? — user30412914
– user30412914, Commented May 16 at 12:38

Kelly Bundy · Accepted Answer · 2025-07-16 12:00:53Z

1

or 0 is a short and quick way to replace negative zero:

for mynumber in -0.0000000001, 0.0000000001, 3, 3.1415927:
    print(round(mynumber, 7) or 0)

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Alternatively, also changing for example 3.0 to 3:

for mynumber in -0.0000000001, 0.0000000001, 3, 3.1415927, 3.0:
    x = round(mynumber, 7)
    if x.is_integer():
        x = int(x)
    print(x)

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edited Jul 16 at 12:00

answered May 16 at 13:16

Kelly Bundy

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3 Comments

MakePeaceGreatAgain Jul 15 at 14:29

what about 3.0? With the above it prints as 3.0, while I want it to print 3.

Kelly Bundy Jul 16 at 12:02

@MakePeaceGreatAgain I don't see a really nice way, but I added a second approach that does it.

MakePeaceGreatAgain Jul 16 at 12:17

yeap, used that already but hoped for a more concise way. Thanks anyway.

kevin41 · Accepted Answer · 2025-05-16 12:48:19Z

0

One option is a quick function using abs() for 0.0 values like the one below.

def round_number(number, digits):
    rounded = round(number, digits)
    return abs(rounded) if rounded == 0.0 else rounded

print(round_number(-0.0000000001, 7))
 >> 0.0
print(round_number(0.0000000001, 7))
 >> 0.0
print(round_number(3, 7))
 >> 3
print(round_number(3.1415927, 7))
 >> 3.1415927

answered May 16 at 12:48

kevin41

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1 Comment

MakePeaceGreatAgain May 16 at 13:14

But I want 0, not 0.0. Anyway that seems really akward. Hoped for a more concise way.

Starship · Accepted Answer · 2025-05-16 15:24:20Z

-1

Just use a special case for if mynumber is -0 when rounded, like this:

if rounded == -0: rounded = 0

answered May 16 at 15:24

Starship

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