Check if a String is a Number Using a Custom is_number() Function

The following example demonstrates how to create a custom function is_number() to determine if a string is a number.

Example (Python 3.0+)

def is_number(s):
    try:
        float(s)  # Try converting to float
        return True
    except ValueError:
        pass

    try:
        import unicodedata  # Handle Unicode strings
        unicodedata.numeric(s)
        return True
    except (TypeError, ValueError):
        pass

    return False

# Test with strings and numbers
print(is_number('foo'))   # False
print(is_number('1'))     # True
print(is_number('1.3'))   # True
print(is_number('-1.37')) # True
print(is_number('1e3'))   # True

# Test with Unicode characters
# Arabic 5
print(is_number('٥'))  # True
# Thai 2
print(is_number('๒'))  # True
# Chinese number
print(is_number('四')) # True
# Copyright symbol
print(is_number('©'))  # False

Output:

False
True
True
True
True
True
True
True
False

In this example, the is_number() function first attempts to convert the string to a float to determine if it’s a valid number. If that fails, it tries using the unicodedata.numeric() method to handle Unicode representations of numbers.

Additional Methods for Checking Numbers

• isdigit(): This method checks if the string consists only of digits. It does not handle floats or negative numbers.

  print('123'.isdigit())  # True
  print('123.45'.isdigit())  # False

• isnumeric(): This method checks if a string contains only numeric characters and works mainly with Unicode objects.

  print('四'.isnumeric())  # True
  print('123'.isnumeric())  # True