Why does 'nothing' count as a string?

[BashBedlam]

allowable_letters = 'abcdefg'
while True :
    test_string = input ('\nEnter a letter or number :')
    if test_string in allowable_letters :
        print (f' "{test_string}" IS in the allowable letters.')
    else :
        print (f' "{test_string}" is NOT in the allowable letters.')

In the above code, entering a letter or number or even a string like ‘abc’ or ‘BashBedlam’ has the correct and expected result. However, if you press enter without typing anything else in, it will tell you that what your input IS in the allowable letters.

Output:
 "" IS in the allowable letters.

If you add print (ord (test_string)) in between the fourth and fifth line, the error will say :

Output:
TypeError: ord() expected a character, but string of length 0 found

So… my question is, why does python think that nothing or a zero length string IS in ‘abcdefg’?

[snippsat]

So… my question is, why does python think that nothing or a zero length string IS in ‘abcdefg’?

A empty string is a substring of every string.

>>> '' in 'hello'
True
>>> '' in 'h'
True
>>> '' in ''
True

The easiest solution for your code is to add list('abcdefg') then do not need to test for empty string.

>>> 'h' in list('hello')
True
>>> '' in list('hello')
False

[Gribouillis]

You can also write this

if test_string and test_string in allowable_letters :
    ...

[BashBedlam]

Thank you both