CODEWITHSUNDEEP
pythonclassattributeerror
Mantas Marcinkus
Mantas Marcinkus

Reputation: 603

Python: instance has no attribute

I have a problem with list within a class in python. Here's my code :

class Residues:
    def setdata(self, name):
        self.name = name
        self.atoms = list()

a = atom
C = Residues()
C.atoms.append(a)

Something like this. I get an error saying:

AttributeError: Residues instance has no attribute 'atoms'

Upvotes: 23

Views: 130658

Answers (2)

Bao April Lei
Bao April Lei

Reputation: 11

the error means the class Residues doesn't have a function call atoms. The solution could be as follows:

class Residues:
    def setdata(self,  atoms, name=None):
        self.name = name
        self.atoms =[]

C = Residues()
C.setdata(atoms= " a ")

Upvotes: 1

NullUserException
NullUserException

Reputation: 85478

Your class doesn't have a __init__(), so by the time it's instantiated, the attribute atoms is not present. You'd have to do C.setdata('something') so C.atoms becomes available.

>>> C = Residues()
>>> C.atoms.append('thing')

Traceback (most recent call last):
  File "<pyshell#84>", line 1, in <module>
    B.atoms.append('thing')
AttributeError: Residues instance has no attribute 'atoms'

>>> C.setdata('something')
>>> C.atoms.append('thing')   # now it works
>>>

Unlike in languages like Java, where you know at compile time what attributes/member variables an object will have, in Python you can dynamically add attributes at runtime. This also implies instances of the same class can have different attributes.

To ensure you'll always have (unless you mess with it down the line, then it's your own fault) an atoms list you could add a constructor:

def __init__(self):
    self.atoms = []

Upvotes: 35

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