How can we do additional testing for python internal like __repr__ ?

Hi there!

Short story: you can just use the built in function repr() to get the value returned by the __repr __ method. Note that repr()'s job is really just to represent the instance as a string, but as the name suggests, if a class has a __repr __ method, it will return what's in there, for example:

>>>test = SomeClass()
>>>print(repr(test))
<SomeClass object at 0x7f57e1444390>

Long story: If it's okay with you, I'll handle __repr __ and __str __ (from now on I'll just call them repr and str just because it's too annoying to keep escaping them from the markdown lol) together. Both are kind of similar, and actually have the same default value for a user defined class - they just return self. That value is:

<x object at y>
# where
# x = the class name
# y  = the memory address the instance is stored at

We can test that here:

class Test:
    value = "Test Data"

instance = Test()
print(instance)
print(repr(instance))

Will print something like:

<Test object at 0x7f57e1418438>
<Test object at 0x7f57e1418438>

People often get confused about the difference between str and repr (I've heard it's often an interview test!) . Bascially repr is the formal/official/internal name to give an instance, and str is the informal/readable/end user name to display to users. For example, python's built in types - int, float, str, dict, etc,etc return the same information from repr and str, because that's the most important information - not where the int with the value 72 is in memory, but that it's the value 72. However for our own defined classes, like Test above, we often want a publicly facing name, that gives the user the important information, and an internal name that gives the developer a bit more info.

class Test:
    value = "Test Data"

    def __str__(self):
        return self.value

    def __repr__(self):
        return "<Instance of {} class, value={}>".format(self.__class__.__name__, self.value)
instance = Test()
print(instance)
print(repr(instance))

Will print:

Test Data
<Instance of Test class, value=Test Data>

Of course, they can print anything, it's just an example... all that matters is to remember repr == internal representation, str == external

Hope it helps :)