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If the string has no letters, both methods return false:
How to Check if a String Is All Uppercase or Lowercase
Theisupper() string method returns true only if all letters in the string are uppercase, and islower() only if all letters are lowercase.>>> a = "UPPERCASE"
>>> b = "lowercase"
>>> c = "MiXeD"
>>> a.isupper()
True
>>> a.islower()
False
>>> b.isupper()
False
>>> b.islower()
True
>>> c.isupper()
False
>>> c.islower()
False
>>>
If the string has no letters, both methods return false:
>>> "!·$%&/)-123".isupper()
False
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