In Python, the isdecimal() method is a quick and easy way to check if a string contains only decimal digits. It works by returning True when the string consists of digits from 0 to 9 and False otherwise. This method is especially useful when we want to ensure that user inputs or string data are strictly numeric without any special characters or spaces.

a = "12345"
print(a.isdecimal())  # This will print True as all characters are digits

b = "12345a"
print(b.isdecimal())  # This will print False because 'a' is not a decimal character

True
False

Syntax of isdecimal()

string.isdecimal()

Parameters

• The isdecimal() method does not take any parameters. It is simply called on a string object.

Return Type

The method returns:

• True if all characters in the string are decimal characters (i.e., digits 0-9).
• False if any character is not a decimal character (including symbols, spaces, letters, etc.) or if the string is empty.

Example 1: Decimal Point Characters

A string that contains a decimal point or any other non-digit characters will return False. For example, strings like "123.45" or "100,000" will fail the check because the period (.) and the comma (,) are not considered decimal digits.

e = "123.45"
print(e.isdecimal())  # False, because '.' is not a decimal character

f = "100,000"
print(f.isdecimal())  # False, because ',' is not a decimal character

False
False

Example 2: Strings with Spaces or Symbols

The isdecimal() method does not consider spaces or symbols as decimal characters. Let’s see an example:

d = "12 34"
print(d.isdecimal())  
# This will print False because there’s a space between the numbers

False

Example 3: Non-Decimal Numeric Characters

There are certain numeric characters from other writing systems or formats that look like digits but are not considered decimal digits in Python. For example, the Arabic-Indic numerals or other scripts that represent numbers differently.

c = "١٢٣٤٥"  # Arabic-Indic numerals
print(c.isdecimal())  # True, because these characters are considered decimal in their script

True

• However, if the characters belong to a different set, like Roman numerals or fractions, the method will return False.

d = "Ⅻ"  # Roman numeral for 12
print(d.isdecimal())  # False, Roman numerals are not decimal

False

Example 4: Negative Numbers or Symbols

The isdecimal() method also returns False when the string contains negative signs (-) or other symbols like currency symbols ($, €, etc.). The presence of any non-decimal character will cause the method to return False.

g = "-12345"
print(g.isdecimal())  # False, because of the negative sign

h = "$12345"
print(h.isdecimal())  # False, because of the '$' symbol

False
False