Extending a class

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Extending a class

 
0
  #1
Dec 16th, 2006
Hi,

I need help please. At first I was understanding the Python language but I got lost somewhere along the line. Can someone please guide me through implementing an addLetterGrade method? I am not very good with computers and I am having a very hard time. This is my first time using a computer language so, please bare with me. I just need someone to help me and maybe answer some of my questions and explain this to me so I can figure out how to do this. Thanks!!


This is what I have so far:
python Syntax (Toggle Plain Text) 
  1.  
  2. import string
  3. import math
  4. class Student:
  5.     def __init__(self, name, hours, qpoints):
  6.         self.name = name
  7.         self.hours = float(hours)
  8.         self.qpoints = float(qpoints)
  9.     def getName(self):
  10.         return self.name
  11.     def getHours(self):
  12.         return self.hours
  13.     def getQpoints(self):
  14.         return self.qpoints
  15.     def gpa(self):
  16.         return self.qpoints/self.hours
  17.  
  18. ##I AM STUCK HERE
  19.     def addLetterGrade(self, Letter, credits):
  20.         self.hours = credits
  21.         for ch in Letter:
  22.             print ord(ch)
  23.         self.qpoints = credits*Letter
  24.         if grade_str = "A":
  25.             grade_str = 4.0
  26.         elif grade_str = "B":
  27.             grade_str = 3.0
  28.         elif grade_str = "C":
  29.             grade_str = 2.0
  30.         elif grade_str = "D":
  31.             grade_str = 1.0
  32.         else:
  33.             grade_str = 0.0
  34.             return
  35.  
  36. def main():
  37.     print "This program is a modified version of the student class. It adds"
  38.     print "a mutator method that records a grade and calculates the GPA for"
  39.     print "the student"
  40.     print
  41.     print
  42.     grade = raw_input("Enter grade for next course, or nothing to finish: ")
  43.     print
  44.     credits = input("Enter the number of credit hours for this course: ")
  45.  
  46.     stu = Student("stu", 0.0, 0.0)
  47.     while 1:
  48.         grade_str = raw_input("Enter grade: ")
  49.         if grade_str == "":
  50.             break
  51.         try:
  52.             grade = float(grade_str)
  53.         except ValueError:
  54.             print "Error, use floating point number"
  55.             return
  56.         credits_str = raw_input("Enter credits: ")
  57.         try:
  58.             credits = float(credits_str)
  59.         except ValueError:
  60.             print "Error, use floating point number"
  61.             return
  62.         stu.addGrade(grade, credits)
  63.  
  64.     if stu.getHours() == 0.0:
  65.         print "Zero credit hours recorded"
  66.     else:
  67.         print "Final GPA = ", stu.gpa()
  68.  
  69.  
  70.  
  71. main()
Last edited by vegaseat; Dec 16th, 2006 at 12:30 pm. Reason: added code tags
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Re: Extending a class

 
0
  #2
Dec 16th, 2006
At first look, when you compare two items use == in your if statements ...
python Syntax (Toggle Plain Text) 
  1.     def addLetterGrade(self, Letter, credits):
  2.         self.hours = credits
  3.         for ch in Letter:
  4.             print ord(ch)
  5.         self.qpoints = credits*Letter
  6.         if grade_str == "A":    # use == !!!!!!!!!!!!
  7.             grade_str = 4.0
  8.         elif grade_str == "B":
  9.             grade_str = 3.0
  10.         elif grade_str == "C":
  11.             grade_str = 2.0
  12.         elif grade_str == "D":
  13.             grade_str = 1.0
  14.         else:
  15.             grade_str = 0.0
  16.             return
May 'the Google' be with you!
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Re: Extending a class

 
0
  #3
Dec 17th, 2006
O.K. This is what I have changed in my program:

import string
import math
class Student:
def __init__(self, name, hours, qpoints):
self.name = name
self.hours = float(hours)
self.qpoints = float(qpoints)
def getName(self):
return self.name
def getHours(self):
return self.hours
def getQpoints(self):
return self.qpoints
def gpa(self):
return self.qpoints/self.hours
def addLetterGrade(self, LetterGrade, credits):
self.hours = credits
self.LetterGrade = Letter
for ch in Letter:
print ord(ch)
self.qpoints = credits*Letter
if Letter == "A":
grade_str = 4.0
elif Letter == "B":
grade_str = 3.0
elif Letter == "C":
grade_str = 2.0
elif Letter == "D":
grade_str = 1.0
else:
grade_str = 0.0
return

def main():
print "This program is a modified version of the student class. It adds"
print "a mutator method that records a grade and calculates the GPA for"
print "the student"
print
print
grade = raw_input("Enter grade for next course, or nothing to finish: ")
print
credits = input("Enter the number of credit hours for this course: ")

stu = Student("stu", 0.0, 0.0)
while 1:
grade_str = raw_input("Enter grade: ")
if grade_str == "":
break
try:
grade = grade_str
except ValueError:
print "Error, use A, B, C, D or F "
return
credits_str = raw_input("Enter credits: ")
try:
credits = float(credits_str)
except ValueError:
print "Error, use floating point number"
return

stu.addLetterGrade(Letter, credits)

if stu.getHours() == 0.0:
print "Zero credit hours recorded"
else:
print "Final GPA = ", stu.gpa()



main()





But it keeps giving me this error:

Enter grade for next course, or nothing to finish: A
Enter the number of credit hours for this course: 3.0
Enter grade: B
Enter credits: 3.0
Traceback (most recent call last):
File "C:\Python23\p6extstclass.py", line 88, in ?
main()
File "C:\Python23\p6extstclass.py", line 78, in main
stu.addLetterGrade(Letter, credits)
NameError: global name 'Letter' is not defined


By the way, thank you for your help so far.
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