What is different between str and 'str'?

[xspam1984]

Assertion errors are thrown for only case 2 and case 4 if the if statements contain:

if type(a) == 'str' and type(b) == 'str' and type(c) ==' str'

why do those fail when 1 and 3 work?

[abeanari]

str is the object that is recognized in python. 'str' is just an unassigned value much like 'hello world' and in this case both of these are of type str