Python Coding Dat 15 | Python Number Crunching: math.ceil() vs round()
Python Number Crunching: math.ceil() vs round()Watch the lesson tutorial 🔻
When working with numbers in Python, you often end up with decimals (floats) that you need to convert into whole numbers (integers). However, not all conversion methods work the same way.
Today, we will look at two distinct ways to handle this: forcing a number up with math.ceil() and finding the nearest number with round().
1. The math.ceil() Function
The ceil() function stands for Ceiling. Just like a ceiling is at the top of a room, this function always rounds the number up to the next highest integer. It doesn't matter if the decimal is small (.1) or large (.9); it always pushes the value upward.
Note: To use this, you must import the math module first.
Practical Examples
import math
# Example 1: Small decimal
print(math.ceil(4.2))
# Output: 5
# Explanation: Even though .2 is small, ceil forces the number UP to the next integer (5).
# Example 2: Large decimal
print(math.ceil(4.8))
# Output: 5
# Explanation: The number is already close to 5, so it goes UP to 5.
# Example 3: Negative numbers
print(math.ceil(-4.2))
# Output: -4
# Explanation: This is tricky! On a number line, -4 is higher (to the right) than -4.2.
# Therefore, the "ceiling" of -4.2 is -4.
Key Takeaway:
math.ceil()never looks down. It always looks for the next highest whole number.
2. The round() Function
The round() function is a built-in Python function (no import needed). It tries to find the nearest whole number.
If the decimal is less than .5, it goes down.
If the decimal is greater than .5, it goes up.
The Tie-Breaker: If the decimal is exactly .5, Python 3 uses a strategy called "Round Half to Even." It rounds to the nearest even number.
Practical Examples
# Example 1: Rounding down
print(round(4.2))
# Output: 4
# Explanation: 4.2 is closer to 4 than it is to 5. So, it rounds down.
# Example 2: Rounding up
print(round(4.8))
# Output: 5
# Explanation: 4.8 is closer to 5. So, it rounds up.
# Example 3: The ".5" Tie-Breaker
print(round(4.5))
# Output: 4
# Explanation: 4.5 is exactly in the middle. Python looks for the nearest EVEN integer.
# Between 4 and 5, 4 is the even number, so it rounds to 4.
# Example 4: Another ".5" check
print(round(5.5))
# Output: 6
# Explanation: Again, it is in the middle. Between 5 and 6, the even number is 6.
# So it rounds up to 6.
Summary Table
| Function | Logic | 4.2 becomes... | 4.8 becomes... |
math.ceil() | Always Up (Highest) | 5 | 5 |
round() | Nearest Neighbor | 4 | 5 |
- by Chirana Nimnaka
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