Add values to a class in Python

Question

Let's say I have the following in Python:

class Test():
    self.value1 = 1
    self.value2 = 2

def setvalue1(self, value):
    self.value1 = value

So one can set up value1 by doing:

Test.setvalue1('Hola')

or

Test.Value1 = 'Hola'

So far so good. My problem is I would like to set the values by reading them somewhere else so for instance I could have the following:

A = [['Value1','Hola'],['Value2','Adios']]

I would like to be able to run something that will do (in pseudo code):

for each in A:
    Test.each[0] = A[1]

Is this possible? Thanks so much!

Is the indention of your code as intended? Is `setvalue1` a member of `Test`? — , May 29 '15 at 12:35
http://stackoverflow.com/questions/285061/how-do-you-programmatically-set-an-attribute-in-python — iced, May 29 '15 at 12:37
isn't `self` undefined at the point you've set `self.value1 = 1`? — Holloway, May 29 '15 at 12:40

score 2 · Answer 1 · answered May 29 '15 at 12:38

2

You could do it like that:

class Test:

    def __init__(self):
        self.val1 = 1



t = Test()
setattr(t, 'val2', 2)

print t.val2

Or like that:

class Test:

    def __init__(self):
        self.val1 = 1

    def setself(self, name, val):
        self.__dict__[name] = val

t = Test()
t.setself('val3', 3)

print t.val3

answered May 29 '15 at 12:38

Maresh

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Unless you know *very exactly* what you're doing, the correct solution is `setattr()`, which will respect the descriptor protocol (computed attributes) while directly setting `self.__dict__` wont. – bruno desthuilliers May 29 '15 at 12:51
Hmm, good to know, I'll look this up – Maresh May 29 '15 at 12:52

James Mills · Answer 2 · 2015-05-29T13:01:16.997

1

Iterate over your data structure and use setattr() on an instance of your class Test:

test = Test()

data = [('Value1', 'Hola'), ('Value2', 'Adios']
for k, v in data:
    setattr(test, k, v)

This kind of data structure btw is generally considered a "key/value" pair and you could use a Python dictionary (dict) here.

Example:

test = Test()

data = {"value1": "Hola", "Value2": "Adios"}
for k, v in data.items()
    setattr(test, k, v)

Now let's fix up your Test class:

class Test(object):

    def __init__(self):
        self.value1 = 1
        self.value2 = 2

    def setvalue1(self, value):
        self.value1 = value

edited May 29 '15 at 13:01

answered May 29 '15 at 12:41

James Mills

18,669
3
49
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In which way is adding useless properties a "fix" ? The only broken things in the OP's class were indentation and the lack of the `__init__` method (or more exactly what should have been in the `__init__` method directly at the class level). – bruno desthuilliers May 29 '15 at 12:55
@brunodesthuilliers You are quite right; I've removed the useless properties :) – James Mills May 29 '15 at 13:01

Add values to a class in Python

2 Answers2