Classes and Methods

[thraxas]

Hello everyone,

started this semester with programming in python, and now we have a task where i dont know how to program it.
We get an UML diagram with two classes, one is "student", the other "uniclass".

class student

• name: str
  
• imt_name: str
  
• semester: int
  ________________
  
• Student(name, imt_name, semester)
  
• __str__(): str
  

class UniClass

• name: str
  ________________
  
• UniClass(name)
  
• enroll_student(student)
  
• __str__(): str
  

Further i get following instructions:

• Use getters for all attributes.
  
• The method __str__ of Student returns the string "Jack (jack99) is in semester 20" for the student with name "Jack", IMT-name "jack99" and semester 20. Use exactly this format.
  
• UniClass uses a set to store enrolled students.
  
• enroll_student only inserts objects that are of type Student. Objects of other types should not be inserted.
  
• The method __str__ of UniClass returns set() if no student is enrolled. For example, one returns "{Jack (jack99) is in semester 20}" and two returns "{Jack (jack99) is in semester 20, Jane (jane100) is in semester 20}" The order does not matter.
  
• Tip: This is easy if you overwrite the __repr__ method of Student. For example, __repr__ is used by the __str__ method of the built-in collection types list, set, and dict to create a string representation of the contained objects.
  

So far I have written this code, but don't know what to do:

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class Student:     def __init__(name, imt_name, semester, *args, **kwargs):         self.name = name         self.imt_name = imt_name         self.semester = semester               def get_name(self):         return self.name           def get_imt_name(self):         return self.imt_name           def get_semester(self):         return self.semester       class UniClass:     def __init__(name, *args, **kwargs):         self.name = name

[Larz60+]

you need to direct the running tasks.

you can add at end of script:

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def run_prog():     student = Student()     uni_class = UniClass()     student1 = student('Harry', ...     ...   if __name__ == '__main__':     run_prog()

[Gribouillis]

To complete Larz60+'s idea, add this to your code

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def run_prog():     jack = Student("Jack", "jack99", 20)     assert str(jack) == "Jack (jack99) is in semester 20"     jane = Student("Jane", "jane100", 20)     assert str(jane) == "Jane (jane100) is in semester 20"     cls = UniClass()     cls.enroll_student(jack)     cls.enroll_student(jane)     assert eval(str(cls)) == {str(jack), str(jane)}   if __name__ == "__main__":     run_prog()

Then change your classes code until the program runs.

[thraxas]

Thanks for your replies.

we have already given something to check it with:

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assert type(Student) is type   student_jack = Student("Jack", "jack99", 20) assert student_jack.name == "Jack" assert student_jack.imt_name == "jack99" assert student_jack.semester == 20   student_jack.semester = 21 assert student_jack.semester == 21     assert isinstance(getattr(Student, "name"), property) assert isinstance(getattr(Student, "imt_name"), property) assert isinstance(getattr(Student, "semester"), property)

There i get the Error:

1	assert isinstance(getattr(Student, "name"), property)

Error:
AttributeError: type object 'Student' has no attribute 'name'

[Gribouillis]

Then you're supposed to implement a property named "name" in the class instead of the get_name() method.

[thraxas]

ok i guess something like that?

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class Student:     def __init__(self, name, imt_name, semester, *args, **kwargs):         self.name = name         self.imt_name = imt_name         self.semester = semester               @property        def name(self):         return self.name           def get_imt_name(self):         return self.imt_name           def get_semester(self):         return self.semester           @name.setter     def name(self, name):         self.name = name               def set_imt_name(self, imt_name):         self.imt_name = imt_name               def set_semester(self, semester):         self.semester = semester           def __str__(self):         return(self.name, self.imt_name, self.semester)       class UniClass:     def __init__(name, *args, **kwargs):         self.name = name

But than i get following error:

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--------------------------------------------------------------------------- RecursionError                            Traceback (most recent call last) <ipython-input-21-66ae99a3ea56> in <module>       2 assert type(Student) is type       3 ----> 4 student_jack = Student("Jack", "jack99", 20)       5 assert student_jack.name == "Jack"       6 assert student_jack.imt_name == "jack99"   <ipython-input-20-2d17b754b915> in __init__(self, name, imt_name, semester, *args, **kwargs)       1 class Student:       2     def __init__(self, name, imt_name, semester, *args, **kwargs): ----> 3         self.name = name       4         self.imt_name = imt_name       5         self.semester = semester   <ipython-input-20-2d17b754b915> in name(self, name)      17     @name.setter      18     def name(self, name): ---> 19         self.name = name      20      21     def set_imt_name(self, imt_name):   ... last 1 frames repeated, from the frame below ...   <ipython-input-20-2d17b754b915> in name(self, name)      17     @name.setter      18     def name(self, name): ---> 19         self.name = name      20      21     def set_imt_name(self, imt_name):   RecursionError: maximum recursion depth exceeded

[Gribouillis]

Use a modified attribute to avoid clashes between the property and the attribute, for example

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@property def name(self):     return self._name

[thraxas]

Use a modified attribute to avoid clashes between the property and the attribute, for example

1 2 3

@property def name(self):     return self._name

Ah thank you very much :)

Now my following code passes the first two tests, but now in the third i get another error.
my code so far:

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class Student:     def __init__(self, name, imt_name, semester, *args, **kwargs):         self.name = name         self.imt_name = imt_name         self.semester = semester               @property        def name(self):         return self._name           @property      def imt_name(self):         return self._imt_name           @property     def semester(self):         return self._semester           @name.setter     def name(self, name):         self._name = name           @imt_name.setter     def imt_name(self, imt_name):         self._imt_name = imt_name           @semester.setter     def semester(self, semester):         self._semester = semester           def __str__(self):         return(self.name, self.imt_name, self.semester)       class UniClass:     def __init__(self, name, *args, **kwargs):         self.name = name         #self.students = students               @property     def name(self):         return self.uname           @name.setter     def name(self, name):         self.uname = name               @property     def students(self):         return self._students           @students.setter     def name(self, students):         self._students = students                      def __str__(self):         return(name)

and the code to test my code:

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programming_class = UniClass("Programming") student_jack = Student("Jack", "jack99", 20) student_jane = Student("Jane", "jane100", 20) assert programming_class.students == set() assert type(programming_class.students) is set programming_class.enroll_student(student_jack) programming_class.enroll_student(student_jane) programming_class.enroll_student("student_jane") assert programming_class.students == {student_jack, student_jane}

with the error:

Error:
---------------------------------------------------------------------------
AssertionError                            Traceback (most recent call last)
<ipython-input-38-dcca7e23946b> in <module>
      3 student_jack = Student("Jack", "jack99", 20)
      4 student_jane = Student("Jane", "jane100", 20)
----> 5 assert programming_class.students == set()
      6 assert type(programming_class.students) is set
      7 programming_class.enroll_student(student_jack)

AssertionError: 

its because of the missing method "enroll_student"?
When i insert this method, how can i test if the given object is from type student?

[Gribouillis]

You need to define self._students = set() in the __init__ method.