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Convert the numeric string with float(), then format the result with .2f when you need exactly two digits after the decimal point:
text = "12.5"
value = float(text)
formatted = f"{value:.2f}"
print(formatted) # 12.50value is a float; formatted is a string. The format specifier controls how the number is written, including trailing zeroes.
Convert a string and format it to two decimal places
Use an f-string with the .2f format specifier after converting the string:
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amount = float(amount_text)
print(f"{amount:.2f}")For fixed-point formatting, the number after the dot is the count of digits after the decimal point. Thus .2f produces exactly two fractional digits. Depending on the value and float representation, formatting may round the displayed result.
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You can use the built-in format() function for the same output:
formatted = format(float("19.995"), ".2f")Python’s format specification documentation describes f precision as the number of digits after the decimal point.
Keep the number and its formatted text distinct
Conversion and formatting do different jobs. float(text) constructs a floating-point value for numeric operations; formatting produces text suitable for a label, report, or display.
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value = float("7.4")
label = f"{value:.2f}" # "7.40"
print(value + 1) # numeric calculation
print(label) # textKeep value for calculations and create label when you need the two-place representation. Formatting does not turn the float into a decimal type or constrain later arithmetic to two decimal places. See Python’s documentation for the float() built-in.
Handle invalid or non-finite input
If a string may not contain a supported number, float() raises ValueError. Catch it where your program can respond appropriately—for example, by showing an error or asking for a corrected value:
def parse_float(text):
try:
return float(text)
except ValueError:
return None
value = parse_float(user_input)
if value is not None:
print(f"{value:.2f}")
else:
print("Enter a valid number.")float() accepts decimal strings with an optional sign and surrounding whitespace, as well as exponent notation such as "1e-003". It also accepts spellings for NaN and infinity. If your application requires ordinary finite numbers, check that separately:
import math
value = float(user_input)
if math.isfinite(value):
print(f"{value:.2f}")
else:
print("Enter a finite number.")Successful conversion alone does not check application-specific limits or rules.
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Choose Decimal for decimal-sensitive arithmetic
For a display label, formatting a float with .2f is usually the direct solution. If the calculation itself must use decimal fixed-point arithmetic, use Decimal and explicitly quantize to two decimal places:
from decimal import Decimal
amount = Decimal("19.995")
rounded = amount.quantize(Decimal("0.01"))
print(f"{rounded:.2f}")Constructing Decimal from the original text avoids first introducing a binary float approximation. The result of quantize() depends on the active Decimal context and its rounding mode, so choose a mode that fits your application. Python documents this fixed-point approach in its Decimal documentation; it does not establish a particular financial or accounting rule.
Do not confuse decimal places with significant digits
Use .2f for exactly two digits after the decimal point. .2g instead requests two significant digits and may omit trailing zeroes, so it does not guarantee a two-place result. Likewise, round(value, 2) returns a numeric result but does not by itself guarantee that its displayed text includes two digits after the decimal point.
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