Python isdigit() Method

What You’ll Learn

The isdigit() method returns True when every character in a string is a digit and the string is not empty. It is one of the most common ways to validate numeric input from users before converting strings to integers or performing calculations.

Definition and Usage

In Python, isdigit() inspects each character in a string. If every character is a digit (including Unicode digit characters and some compatibility forms like superscript digits) and the string has at least one character, it returns True. Otherwise it returns False. For example, "12345".isdigit() is True, but "Hello123".isdigit() is False because of the letters.

📝 Syntax

The isdigit() method takes no parameters:

string.isdigit()

Syntax Rules

• string — any valid Python str object.
• Return value — True if all characters are digits and the string is non-empty; otherwise False.
• No arguments — passing arguments raises TypeError.
• Read-only — the original string is never modified.
• Unicode — accepts digit characters from various scripts, plus some compatibility digits that isdecimal() rejects.

↩ Return Value

isdigit() always returns a boolean. It returns True only when the string contains one or more characters and every character is a digit. It returns False for empty strings, strings with letters, and strings with punctuation such as ., -, or spaces.

print("12345".isdigit())    # True
print("Hello123".isdigit()) # False (letters)
print("".isdigit())         # False (empty)
print("3.14".isdigit())      # False (decimal point)
print("-42".isdigit())       # False (minus sign)

Examples Gallery

Run these examples in any Python 3 interpreter. Each one shows a common numeric validation scenario.

numeric_string = "12345"
result = numeric_string.isdigit()

print("Text:  ", numeric_string)
print("Result:", result)

Text:   12345
Result: True

text = "Hello123"
result = text.isdigit()

print("Text:  ", text)
print("Result:", result)

Text:   Hello123
Result: False

samples = ["", "007", "3.14", "-42", "12 34"]

for text in samples:
    print(repr(text), "→", text.isdigit())

'' → False
'007' → True
'3.14' → False
'-42' → False
'12 34' → False

def double_if_numeric(value):
    if not value:
        return "Input cannot be empty."
    if not value.isdigit():
        return "Please enter digits only."
    return f"Double of {value} is {int(value) * 2}"

for entry in ["10", "10.5", "ten"]:
    print(repr(entry), "→", double_if_numeric(entry))

'10' → Double of 10 is 20
'10.5' → Please enter digits only.
'ten' → Please enter digits only.

samples = ["12345", "\u0661\u0662\u0663", "\u2460", "\u00b2"]

for text in samples:
    print(repr(text))
    print("  isdigit():  ", text.isdigit())
    print("  isdecimal():", text.isdecimal())
    print()

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

'١٢٣'
  isdigit():   True
  isdecimal(): True

'①'
  isdigit():   True
  isdecimal(): False

'²'
  isdigit():   True
  isdecimal(): False

🚀 Common Use Cases

• Menu choices — verify the user typed a numeric option before processing.
• Quantity fields — ensure order counts contain digits only.
• Pre-conversion checks — call isdigit() before int(text).
• Game scores — validate that a score entry is numeric text.
• Data filtering — identify digit-only columns in imported text data.

📝 Notes

• Decimal points, minus signs, plus signs, and spaces all cause False.
• An empty string "" always returns False—there must be at least one digit.
• isdigit() accepts some Unicode compatibility digits that isdecimal() rejects.
• Negative numbers and floats fail because - and . are not digits.
• isdigit() does not check length—combine it with len() for fixed-width codes.

💡 Best Practices