how do you reference a class instance with a variable in python?

Question

I'm new to Python and I've searched for an answer but can't find one. Maybe I'm just asking it the wrong way...

As an example, if I have a class as follows:

class Person(object):
    def __init__(self, name):
        self.name = name

I create a couple instances as follows and can get their attributes like this:

person1 = Person("John")
person2 = Person("Mike")
print person1.name
print person2.name

What I want to do is substitute "personX" with a variable, and this is the part I haven't figured out yet. I'd like to to use this to iterate through a list of names that map to class instances and get/set their attributes.

name1 = "person1"
print "%s".name % (name1) <--- this fails with "AttributeError: 'str' object has no attribute 'name'

Consider using a list or a map for storing the instances rather that individual variables - this way you can easily iterate over any number of those. Coming back to your original questions, `eval` could be used for getting a variable by name, but that should preferably be avoided. — Vadim Landa, May 21 '15 at 12:45

deceze · Accepted Answer · 2015-05-22T12:04:00.570

1

Whenever you want to create variableX where X is an incrementing number, you really want a list:

people = []
people.append(Person('John'))
people.append(Person('Mike'))

for person in people:
    print person.name

print people[0].name

edited May 22 '15 at 12:04

answered May 21 '15 at 12:46

deceze

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Or a dictionary, see below. – Malik Brahimi May 21 '15 at 12:50
Why would I want `people['person0']` over `people[0]`. That's just redundant. – deceze May 21 '15 at 12:51
Well, he did after all want to map a name to a Person object. – Malik Brahimi May 21 '15 at 12:52
If the "name" is just `"person1"`, then no, that's not really what they want. – deceze May 21 '15 at 12:53
He wanted a variable name, but `exec` is a bad option to do that. So a dictionary would be the best bet. – Malik Brahimi May 21 '15 at 12:55
Sure, if the name actually matters and a key-value mapping is required, a dictionary is the answer. I simply don't see that from the given sample. – deceze May 21 '15 at 12:56
Thanks deceze. That's what I needed. Note the typo and that it should be "print poeple[0].name" in your example. – zend0 May 21 '15 at 22:59

score 0 · Answer 2 · answered May 21 '15 at 12:46

0

Use eval() to get instance referenced by the created string this way

name1 = "person1"
print eval(name1).name

answered May 21 '15 at 12:46

farhawa

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don't use `eval()` if you can reasonably avoid it. – knitti May 21 '15 at 12:48
this solve his problem and can be the solution he's looking for.. but you'r wright – farhawa May 21 '15 at 12:49
Don't take everything an OP asks literally if it's a bad idea. – deceze May 21 '15 at 12:52

Malik Brahimi · Answer 3 · 2015-05-21T12:58:29.370

0

Typically, this is considered bad practice, especially with the use of eval and exec to do so:

people = {'person1': Person('Bob'), 'person2': Person('Sam')}

edited May 21 '15 at 12:58

answered May 21 '15 at 12:49

Malik Brahimi

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how do you reference a class instance with a variable in python?

3 Answers3