Python: Concatenate two strings for getting a variable from a class

Question

I have a Python class , having some variables. The definition of the class is as follows:

class student:
    def __init__(self,name,rollno,DOB,branch):
       self.name=name
       self.rollno=rollno
       self.DOB=DOB
       self.branch=branch
       self.books=[]
       self.fines=[]

I am adding new attributes for a student , and need to store the corresponding values as well (for future use). This is done using the setattr method, and works fine.

Code snippet:

setattr(student,"date_of_join",date())

Now I am approaching the problem as, if the user adds a new attribute (say, "date_of_join"), then I update a list (studattr), initially containing ["name","rollno",DOB","branch","books","fines"] to update the list of attributes. This means that the updated list will also have "date_of_join" now appended to it.

Now if I want to access this list of attributes of a student Instance, then how do I do it? ( Since the records are dynamically updated, and let us suppose I have to access x.date_of_join, then how do I join the two strings? Is there anything similar to python's os.path.join, or rather linux's system call, (merging two strings)? )

Problem:

for attribute in studattr:
    print attribute,x.attribute

{ This throws an Exception since the instance x has no variable or method named "attribute")

PS: I tried using inspect,inspect.getmembers(x) as well as dirs(x), vars(x) ,(mentioned on stackoverflow), but it only gives me a list of variables/methods in main class body and not in init.

Instead of using an object instance on which you set attributes, isn't a normal dictionary a better fit for what you're trying to do? — RemcoGerlich
– RemcoGerlich, Commented Feb 10, 2014 at 13:24
If you're getting a list of variables/methods in the main class body, then you're not running dir on the instance. — Ricardo Cárdenes
– Ricardo Cárdenes, Commented Feb 10, 2014 at 13:26

Alfe · Accepted Answer · 2014-02-10 13:26:52Z

5

Use getattr() to access dynamic attributes:

for attr in student.studattr:
    print attr, getattr(student, attr)

or use vars() will give you a dictionary of current attributes on a student:

for attr, value in vars(student).iteritems():
    print attr, value

edited Feb 10, 2014 at 13:26

Alfe

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answered Feb 10, 2014 at 13:23

Martijn Pieters

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1 Comment

Dref D Over a year ago

Thanks! Worked perfectly!

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