gh-106318: Add example for str.isdecimal()

Author: adorilson

Doc/library/stdtypes.rst

@@ -2008,7 +2008,16 @@ expression support in the :mod:`re` module).
    otherwise. Decimal characters are those that can be used to form
    numbers in base 10, e.g. U+0660, ARABIC-INDIC DIGIT
    ZERO.  Formally a decimal character is a character in the Unicode
-   General Category "Nd".
+   General Category "Nd". For example::
+
+   .. doctest::
+
+      >>> '0123456789'.isdecimal()
+      True
+      >>> '٠١٢٣٤٥٦٧٨٩'.isdecimal() # ARABIC-INDIC DIGIT ZERO TO NINE
+      True
+      >>> 'alphabetic'.isdecimal()
+      False
 
 
 .. method:: str.isdigit()
@@ -2020,7 +2029,6 @@ expression support in the :mod:`re` module).
    like the Kharosthi numbers.  Formally, a digit is a character that has the
    property value Numeric_Type=Digit or Numeric_Type=Decimal.
 
-
 .. method:: str.isidentifier()
 
    Return ``True`` if the string is a valid identifier according to the language