python dynamically create attributes class

Question

I am facing issues adding class attributes dynamically from a list of strings, consider the following scenario:

This is my class:

class Customer(object):
    def __init__(self,**kw):
        self.__dict__ = kw

    def add_attributes(self,**kw):
        self.__dict__.update(kw)  

#a group of attributes i want to associate with the class
list = []
list.append("name")
list.append("age")
list.append("gender")

Customer c

for i in list:
    # i is the attribute name for the class
    c.add_attributes( i = "test")

The issue seems to be the fact that it is treating the attribute name as a string, can someone please advise

OT: do not use 'list' as a variable, otherwise this will override standard 'list' function... — Don
– Don, Commented Feb 14, 2014 at 13:11

Ashwini Chaudhary · Accepted Answer · 2014-02-14 12:53:16Z

2

i = "test" is actually converted to {'i':'test'} when passed to **kwargs inside add_attributes, so you need to do something like this:

for i in my_list:
    c.add_attributes(**{ i : "test"})

answered Feb 14, 2014 at 12:53

Ashwini Chaudhary

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4 Comments

Martijn Pieters Over a year ago

This produces dictionaries with i as the key, and 'test' as the value, then uses the **kw syntax to apply the dictionary as keyword arguments to the c.add_attributes() method.

Ashwini Chaudhary Over a year ago

@godzilla Read about keyword arguments: docs.python.org/2/tutorial/controlflow.html#keyword-arguments

godzilla Over a year ago

thanks Ashwini, i will do, one last question, if i wanted to iterate over the attributes and print them along with their corresponding values, how would i go about doing that?

Ashwini Chaudhary Over a year ago

@godzilla self.__dict__.items() will return key, value pairs.

Sunny Nanda · Accepted Answer · 2014-02-14 12:57:54Z

1

Instead of directly updating __dict__, you can use the setattr builtin method:

for i in list:
    # i is the attribute name for the class
    setattr(c, i, "test")

In my opinion, playing with internal attributes should be the last resort.

answered Feb 14, 2014 at 12:57

Sunny Nanda

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Comments

unutbu · Accepted Answer · 2014-02-14 13:06:06Z

0

Instead of a for-loop, you could use dict.fromkeys:

c.add_attributes(**dict.fromkeys(seq, "test"))

since

In [13]: dict.fromkeys(seq, "test")
Out[13]: {'age': 'test', 'gender': 'test', 'name': 'test'}

The ** tells Python to unpack the dict into keyword arguments. The syntax is explained here and in the docs, here.

By the way, it's best not to use list as a variable name, since it makes it difficult to access the builtin of the same name.

edited Feb 14, 2014 at 13:06

answered Feb 14, 2014 at 12:59

unutbu

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