Python Program to Check if a Number is Positive, Negative, or 0

This is a simple problem statement in which we need to find whether a number is positive, negative or zero using Python. Any number greater than zero is positive, and any number less than zero is called a negative number. The number may be a float or an integer.

This article discusses simple ways to check the number using Python examples.

1. Using if-elif-else Statements

This is the most straightforward way to check the sign of a number in Python using if-elif-else.

• If num is greater than 0, it is positive.
• Else if num is less than 0, it is negative.
• Else num is equal to 0, it is zero.

Code Example

num = 10

if num > 0:
    print("Positive")
elif num < 0:
    print("Negative")
else:
    print("Zero")
     
# Output:
# PositiveCode language: Python (python)

2. Using Ternary (Conditional) Operator

Python doesn’t have a direct ternary operator like other languages, but you can simulate it with conditional expressions to find if the number is positive, negative or zero.

This is a more compact way of writing conditions. The conditional expressions are evaluated from left to right.

• If num > 0, it prints “Positive”.
• Else if num < 0, it prints “Negative”.
• Otherwise, it prints “Zero”.

Code Example

num = -10
sign = "Positive" if num > 0 else "Negative" if num < 0 else "Zero"
print(sign)

# Output:
# NegativeCode language: Python (python)

3. Using Lambda function

A lambda function in Python is a small, anonymous function that is defined using the lambda keyword. It can have multiple arguments but only one expression, which is evaluated and returned.

lambda arguments: expression

• lambda → Keyword to define the function.
• arguments → Input parameters (similar to function arguments).
• expression → A single operation that returns a result.

This is more concise way to perform the same check in a more functional programming style. It works similar to the ternary operator but wrapped inside a lambda.

Code Example

num = -10
check_sign = lambda num: "Positive" if num > 0 else "Negative" if num < 0 else "Zero"
print(check_sign(num))

# Output:
# NegativeCode language: Python (python)

4. Using NumPy’s sign Function

If you are working with NumPy, a popular library for numerical computing, you can use numpy.sign() that returns the sign of a number or an array of numbers.

numpy.sign(num) returns 1 for positive numbers, -1 for negative numbers, and 0 for zero. Based on this, you can print the corresponding message.

Note: The Numpy library is not bundled with the default Python installation. We need to install it separately.

Code Example

import numpy as np

num = 10
sign = np.sign(num)

if sign == 1:
    print("Positive")
elif sign == -1:
    print("Negative")
else:
    print("Zero")

# Output:
# PositiveCode language: Python (python)

Summary

There are various ways in Python to check if a number is positive, negative, or zero, ranging from basic conditional checks to more functional and library-based approaches.