def check_object(<EOL>state, index, missing_msg=None, expand_msg=None, typestr="<STR_LIT>"<EOL>):
<EOL>if v2_only():<EOL><INDENT>extra_msg = "<STR_LIT>"<EOL>state.assert_root("<STR_LIT>", extra_msg=extra_msg)<EOL><DEDENT>if missing_msg is None:<EOL><INDENT>missing_msg = "<STR_LIT>"<EOL><DEDENT>if expand_msg is None:<EOL><INDENT>expand_msg = "<STR_LIT>"<EOL><DEDENT>if (<EOL>not isDefinedInProcess(index, state.solution_process)<EOL>and state.has_different_processes()<EOL>):<EOL><INDENT>raise InstructorError(<EOL>"<STR_LIT>"<EOL>% index<EOL>)<EOL><DEDENT>append_message = {"<STR_LIT>": expand_msg, "<STR_LIT>": {"<STR_LIT:index>": index, "<STR_LIT>": typestr}}<EOL>fallback = lambda: ObjectAssignmentParser.get_part(index)<EOL>stu_part = state.ast_dispatcher("<STR_LIT>", state.student_ast).get(index, fallback())<EOL>sol_part = state.ast_dispatcher("<STR_LIT>", state.solution_ast).get(index, fallback())<EOL>_msg = state.build_message(missing_msg, append_message["<STR_LIT>"])<EOL>state.do_test(DefinedProcessTest(index, state.student_process, Feedback(_msg)))<EOL>child = part_to_child(<EOL>stu_part, sol_part, append_message, state, node_name="<STR_LIT>"<EOL>)<EOL>return child<EOL>
Check object existence (and equality)

    Check whether an object is defined in the student's process, and zoom in on its value in both
    student and solution process to inspect quality (with has_equal_value().

    In ``pythonbackend``, both the student's submission as well as the solution code are executed, in separate processes.
    ``check_object()`` looks at these processes and checks if the referenced object is available in the student process.
    Next, you can use ``has_equal_value()`` to check whether the objects in the student and solution process correspond.

    Args:
        index (str): the name of the object which value has to be checked.
        missing_msg (str): feedback message when the object is not defined in the student process.
        expand_msg (str): If specified, this overrides any messages that are prepended by previous SCT chains.

    :Example:

        Suppose you want the student to create a variable ``x``, equal to 15: ::

            x = 15

        The following SCT will verify this: ::

            Ex().check_object("x").has_equal_value()

        - ``check_object()`` will check if the variable ``x`` is defined in the student process.
        - ``has_equal_value()`` will check whether the value of ``x`` in the solution process is the same as in the student process.

        Note that ``has_equal_value()`` only looks at **end result** of a variable in the student process.
        In the example, how the object ``x`` came about in the student's submission, does not matter.    
        This means that all of the following submission will also pass the above SCT: ::

            x = 15
            x = 12 + 3
            x = 3; x += 12

    :Example:

        As the previous example mentioned, ``has_equal_value()`` only looks at the **end result**. If your exercise is
        first initializing and object and further down the script is updating the object, you can only look at the final value!

        Suppose you want the student to initialize and populate a list `my_list` as follows: ::

            my_list = []
            for i in range(20):
                if i % 3 == 0:
                    my_list.append(i)

        There is no robust way to verify whether `my_list = [0]` was coded correctly in a separate way.
        The best SCT would look something like this: ::

            msg = "Have you correctly initialized `my_list`?"
            Ex().check_correct(
                check_object('my_list').has_equal_value(),
                multi(
                    # check initialization: [] or list()
                    check_or(
                        has_equal_ast(code = "[]", incorrect_msg = msg),
                        check_function('list')
                    ),
                    check_for_loop().multi(
                        check_iter().has_equal_value(),
                        check_body().check_if_else().multi(
                            check_test().multi(
                                set_context(2).has_equal_value(),
                                set_context(3).has_equal_value()
                            ),
                            check_body().set_context(3).\\
                                set_env(my_list = [0]).\\
                                has_equal_value(name = 'my_list')
                        )
                    )
                )
            )

        - ``check_correct()`` is used to robustly check whether ``my_list`` was built correctly.
        - If ``my_list`` is not correct, **both** the initialization and the population code are checked.

    :Example:

        Because checking object correctness incorrectly is such a common misconception, we're adding another example: ::

            import pandas as pd
            df = pd.DataFrame({'a': [1, 2, 3], 'b': [4, 5, 6]})
            df['c'] = [7, 8, 9]

        The following SCT would be **wrong**, as it does not factor in the possibility that the 'add column ``c``' step could've been wrong: ::

            Ex().check_correct(
                check_object('df').has_equal_value(),
                check_function('pandas.DataFrame').check_args(0).has_equal_value()
            )

        The following SCT would be better, as it is specific to the steps: ::

            # verify the df = pd.DataFrame(...) step
            Ex().check_correct(
                check_df('df').multi(
                    check_keys('a').has_equal_value(),
                    check_keys('b').has_equal_value()
                ),
                check_function('pandas.DataFrame').check_args(0).has_equal_value()
            )

            # verify the df['c'] = [...] step
            Ex().check_df('df').check_keys('c').has_equal_value()

    :Example:

        pythonwhat compares the objects in the student and solution process with the ``==`` operator.
        For basic objects, this ``==`` is operator is properly implemented, so that the objects can be effectively compared.
        For more complex objects that are produced by third-party packages, however, it's possible that this equality operator is not implemented in a way you'd expect.
        Often, for these object types the ``==`` will compare the actual object instances: ::

            # pre exercise code
            class Number():
                def __init__(self, n):
                    self.n = n

            # solution
            x = Number(1)

            # sct that won't work
            Ex().check_object().has_equal_value()

            # sct
            Ex().check_object().has_equal_value(expr_code = 'x.n')

            # submissions that will pass this sct
            x = Number(1)
            x = Number(2 - 1)

        The basic SCT like in the previous example will notwork here.
        Notice how we used the ``expr_code`` argument to _override_ which value `has_equal_value()` is checking.
        Instead of checking whether `x` corresponds between student and solution process, it's now executing the expression ``x.n``
        and seeing if the result of running this expression in both student and solution process match.