isupper

Isupper is a name given to a function or method used in several programming languages to test whether the alphabetic characters in a string are all uppercase. The check typically ignores digits, punctuation, and other non-cased characters, and it requires at least one cased character to be present for a positive result.

Python provides a string method named isupper, invoked as s.isupper(). It is Unicode-aware: it returns True if every cased character in the string is uppercase and there is at least one cased character; non-cased characters are ignored. It returns False for the empty string or for strings with any lowercase cased character. Examples: 'FOO'.isupper() is True; 'Foo'.isupper() is False; '123'.isupper() is False; '1A'.isupper() is True.

In C, isupper is a function declared in ctype.h. It tests whether a given character is an uppercase letter according to the current locale. The argument must be representable as unsigned char or EOF. The result is nonzero if uppercase, and zero otherwise. Behavior is locale-dependent and not defined for multibyte characters beyond the current locale.

Other languages provide similar functionality under different names. Java offers Character.isUpperCase for single characters, while many languages validate strings by comparing them to their uppercase form, such as s.equals(s.toUpperCase()). In Unicode, casing rules may vary by language and implementation.

Common uses include input validation, formatting checks, and user interface constraints. Limitations include differing definitions of a cased character, locale dependencies in some environments, and edge cases such as strings containing no cased characters.