Formatting floats without trailing zeros

python

precision-engineering

formatting

decimal

byNikita Barsukov·Jan 19, 2025

To format floating point numbers effectively and strip trailing decimals and zeros, resort to Python's format function or utilize an f-string with :.2f (modify 2 to adjust required decimals). Implement .rstrip('0').rstrip('.') for the purpose of removing redundant zeros:

num = 3.140000
# Did anyone say "doctor"? Because we're about to trim some zeros!
formatted = f"{num:.2f}".rstrip('0').rstrip('.')  # Outputs: "3.14"

Remember to postpend .rstrip('0').rstrip('.') to ensure your output is succinct and free of trailing zeros.

Managing precision with 'format'

To evade the uncalled-for scientific notation, and get finer control over precision, format function comes to your aid:

num = 1234.56789
# Ready to strip? Let's go streaking!
formatted = format(num, '.15f').rstrip('0').rstrip('.')
print(formatted)  # Outputs: "1234.56789"

The .15f here regulates the precision—feel free to modify as per your necessities.

Harness 'Decimal' for precision

Decimal module of Python boasts of a normalize() method that takes care of decimal precision and abstains from trailing zeros and exponential representation:

from decimal import Decimal

num = '1234.56789000'
# Trimming the fat... I mean, zeros.
formatted = Decimal(num).normalize()  # Outputs: Decimal('1234.56789')

Note that you initialize Decimal with a string to prevent precision loss.

Tackling edge cases

There might be scenarios where the output turns out to be "-0". Handle such cases with:

result = '-0'
# Because nobody likes a negative zero.
formatted = '0' if result == '-0' else result

For neatly formatting complete numbers such as 10, 100, 1000, bring quantize function into the picture:

from decimal import Decimal, ROUND_DOWN

num = '1000.0000'
# Cutting down those zeros faster than a lumberjack!
formatted = Decimal(num).quantize(Decimal('1.'), rounding=ROUND_DOWN)
print(formatted)  # Outputs: "1000"

Different strokes for different folks: formatting routes

There are multiple ways to skin this cat; different methods work for different contexts. Let's examine a couple:

The `.format()` approach

The traditional format "{:f}".format(x) serves the purpose too:

num = 42.0000
# That's one small step for a coder, one giant leap for code readability!
formatted = "{:f}".format(num).rstrip('0').rstrip('.')
print(formatted)  # Outputs: "42"

Dynamic precision with `Decimal`

If dynamically adjusting precision aligns with your needs, use context settings of the Decimal module:

from decimal import Decimal, getcontext

getcontext().prec = 10  # Adjust precision to 10
num = Decimal('3.000') / Decimal('1.100')
print(num.normalize())  # Outputs: "2.7272727273"

Watch out for `%g`

Although %g format specifier strives to eliminate trailing zeros, it may stumble into scientific notation:

num = 0.0000012345
# "%g": A surprise, to be sure, but a welcome one. Or is it...? 
formatted = '%g' % num
print(formatted)  # Might output: "1.2345e-06"

Eschew this technique if scientific notation isn't your cup of tea.

Precision: do or die situations

In mission-critical implementations, precision is of the essence. Let's ensure it:

Kick off Decimal with a string or integer—floating point numbers might introduce premature rounding.
Always explicitly round with quantize to control the rounding craze and protect yourself from unexpected rounding that might occur due to default settings.

Common issues and their fixes

Some potential problems and their troubleshooting:

Negative zero 'issue': Swap '-0' with '0' using a conditional statement.
Whole number formatting: Apply Decimal's quantize method with adequate rounding type.
Large floats resulting in scientific notation: Utilize format function with ample precision value followed by trivia stripping techniques.