Question

PYTHON 3.8

class student():

def __init__(self, name = 'Bill', grade = 9, subjects = ['math','science']):
self.name = name
self.grade = grade
self.subjects = subjects

  def add_subjects(self):
      print('Current subjects:')
      print(self.subjects)
      more_subjects = True
      while more_subjects == True:
          subject_input = input('Enter a subject to add: ')
          if subject_input == '':
              more_subjects = False
              print(self.subjects)
          else:
              self.subjects.append(subject_input)
              print(self.subjects)

m = student()
d = student()

why is it that when i execute function add_subjects that it adds the subject to both class objects

for example m.add_subjects() will add the subject to m and d

Answer 1

For proper Explanation let us add two extra line in the code given (Last two lines) to call the function add_subjects() using both the objects m and d.

Code :

class student():
def __init__(self, name = 'Bill', grade = 9, subjects = ['math','science']):
self.name = name
self.grade = grade
self.subjects = subjects

def add_subjects(self):
print('Current subjects:')
print(self.subjects)
more_subjects = True
while more_subjects == True:
subject_input = input('Enter a subject to add: ')
if subject_input == '':
more_subjects = False
print(self.subjects)
else:
self.subjects.append(subject_input)
print(self.subjects)

m = student()
d = student()
m.add_subjects() #Calling function add_subjects using object m
d.add_subjects() #Calling function add_subjects using object d

Output :

Explanation :

When we call m.add_subjects(), according to the definition of the function add_subjects it will first print the already added subjects i.e.

Current subjects:                                                                                                               

['math', 'science']

Now,it will takes the subject to be added, Here I have added English subjected so it will displays this as following:

Enter a subject to add: English                                                                                                 

['math', 'science', 'English']

To get out of m.add_subjects(), we have given an empty value ('') to the subjected to be added, before getting out it will again print the subjects added:

Enter a subject to add:                                                                                                         

['math', 'science', 'English']

Now, again d.add_subjects(), according to the definition of the function add_subjects it will first print the already added subjects i.e.

Current subjects:                                                                                                               

['math', 'science', 'English']

• Now, it has observed that when we call the d.add_subjects() , the subject we added in m.add_subjects() also appears here, this is because you are calling the same function add_subjects() of the class.
• Also m.add_subjects() has appended the parameters subjects during its execution. Thus when you call the function d.add_subjects(), it will use the subjects list that is appended previously by m.add_subjects().