How to Check if a String is Numeric in Python

In Python, you can check if a string is numeric using the str.isdigit(), str.isnumeric(), or str.isdecimal() methods. These methods return True if all characters in the string are numeric digits and False otherwise.

Syntax

Python provides three main string methods to check if a string contains only numeric characters:

• str.isdigit(): Returns True if all characters are digits (0-9).
• str.isnumeric(): Returns True if all characters are numeric, including digits and numeric characters from other languages.
• str.isdecimal(): Returns True if all characters are decimal characters (0-9).

python

string.isdigit()
string.isnumeric()
string.isdecimal()

Example

This example shows how to use isdigit(), isnumeric(), and isdecimal() to check different strings for numeric content.

python

samples = ['12345', '²345', '123.45', 'Ⅷ', '123a']

for s in samples:
    print(f"Checking '{s}':")
    print(f"  isdigit(): {s.isdigit()}")
    print(f"  isnumeric(): {s.isnumeric()}")
    print(f"  isdecimal(): {s.isdecimal()}")
    print()

Output

Checking '12345':
  isdigit(): True
  isnumeric(): True
  isdecimal(): True

Checking '²345':
  isdigit(): False
  isnumeric(): True
  isdecimal(): False

Checking '123.45':
  isdigit(): False
  isnumeric(): False
  isdecimal(): False

Checking 'Ⅷ':
  isdigit(): False
  isnumeric(): True
  isdecimal(): False

Checking '123a':
  isdigit(): False
  isnumeric(): False
  isdecimal(): False

Common Pitfalls

Many beginners expect isdigit() to return True for strings with decimal points or negative signs, but it does not. Also, isnumeric() includes numeric characters like superscripts and fractions, which may not be what you want.

To check if a string represents a valid number including decimals or negatives, use float() conversion inside a try-except block instead.

python

s = '-123.45'

# Wrong way: isdigit() returns False
print(s.isdigit())  # False

# Right way: try converting to float
try:
    num = float(s)
    print(True)
except ValueError:
    print(False)

Output

False
True

Quick Reference

Method	Description	Example Returns True For
isdigit()	Checks if all characters are digits (0-9)	'12345'
isnumeric()	Checks if all characters are numeric (digits + numeric chars)	'12345', '²345', 'Ⅷ'
isdecimal()	Checks if all characters are decimal digits (0-9)	'12345'

Key Takeaways

Use str.isdigit() to check if a string contains only digit characters (0-9).

str.isnumeric() is broader and includes numeric characters like superscripts and fractions.

str.isdecimal() is stricter and only returns True for decimal digits.

For numbers with decimals or signs, use float conversion with try-except instead of these methods.

These methods return False for empty strings or strings with spaces or symbols.