Discard a numeric value’s fractional part toward zero.
What You Will Learn
trunc(value) is based on the __trunc__ protocol and differs from floor() for negative numbers.
For floating-point results, remember that stored values are approximations. Rounding a displayed value does not change the exact value used by later calculations.
Step-by-Step Example
The example below makes the behavior visible with small input values that you can change safely.
import math
print(math.trunc(-3.9))How the Example Works
- The imports provide the standard-library tools used in the demonstration: math.
- The print() calls make the return values or state visible so you can compare them with the explanation and check your prediction.
For the chosen input, the expression math.trunc(-3.9) prints -3. Compare that result with the rule above before you change the argument.
Expected output from the example:
-3Another Example: Compare the Results
Try a second input and compare it with the first. Notice whether the result changes in type, value, order, or number of items.
import math
print(math.trunc(3.99), math.trunc(-3.99))Expected output:
3 -3When You Would Use This
This operation can support measurements, numeric reports, simulations, or input validation. Choose integer operations when exact integer answers are required, and check floating-point rounding when displaying measured values. Validate units and input domains before using the result in a calculation.
Practice: Modify the Code
Compare trunc(), floor(), and ceil() for -2.7.
Verify the changed output against the behavior described above, including the relevant invalid or boundary case.
For complete parameters and version details, consult the official Python documentation.
Common Beginner Mistakes
- Expecting truncation to round to the nearest integer.
- Skipping invalid or boundary inputs when adapting a numeric function to real user data.
Key Takeaways
- Discard a numeric value’s fractional part toward zero.
- trunc(value) is based on the __trunc__ protocol and differs from floor() for negative numbers.
- Apply this operation only after checking the assumptions and input conditions shown in the example.