Implement IsNumber() function in Python

In this article, we will learn how to implement an isNumber() function in Python. This custom function checks whether a given string represents a valid number and returns True or False accordingly.

The function uses exception handling with try and except statements to determine if a string can be converted to a number. This approach is efficient because Python's built-in conversion functions will raise a ValueError if the string is not a valid number.

Basic Implementation

Here's a simple implementation that checks for integers ?

def isNumber(s):
    # Handle negative numbers
    if s[0] == '-':
        s = s[1:]
    
    # Exception handling
    try:
        n = int(s)
        return True
    # Catch exception if any error is encountered
    except ValueError:
        return False

# Test cases
inp1 = "786"
inp2 = "-786"
inp3 = "Tutorialspoint"

print(isNumber(inp1))
print(isNumber(inp2))
print(isNumber(inp3))

True
True
False

Enhanced Version for Floats

To handle both integers and floating-point numbers, we can use float() instead ?

def isNumber(s):
    try:
        float(s)
        return True
    except ValueError:
        return False

# Test with different number formats
test_cases = ["123", "-45.67", "3.14159", "abc", "12.34.56", ""]

for case in test_cases:
    print(f"'{case}' is number: {isNumber(case)}")

'123' is number: True
'-45.67' is number: True
'3.14159' is number: True
'abc' is number: False
'12.34.56' is number: False
'' is number: False

Using Built-in Methods

Python provides built-in string methods for specific number checks ?

# Using built-in methods
test_string = "12345"
print(f"isdigit(): {test_string.isdigit()}")
print(f"isnumeric(): {test_string.isnumeric()}")
print(f"isdecimal(): {test_string.isdecimal()}")

# Comparison with custom function
def isNumber(s):
    try:
        float(s)
        return True
    except ValueError:
        return False

print(f"Custom isNumber(): {isNumber(test_string)}")

isdigit(): True
isnumeric(): True
isdecimal(): True
Custom isNumber(): True

Comparison of Methods

Conclusion

The custom isNumber() function using exception handling provides the most flexible solution for detecting numeric strings. Use int() for integers only or float() for comprehensive number validation including decimals and negative numbers.