Adding metadata to existing python objects

Question

I am currently reading lines from a .csv file and storing the data in a list of array.array('f') objects. Since I will be passing the individual lines to different processes I would like to store an (line) id with every array.array object.

I know I can do this obviously by defining a new class and encapsulating the data, but I was wondering if there is a different way by adding dynamically a custom attribute to array.array. The benefit would be not having an additional look up when accessing the data itself and not having to define a class with just the id and the data.

I know a list of tuples are an option too, but in the near future I will want to store mutable attributes.

What is the python way to do this?

array.array objects don't allow for arbitrary attributes, no. Encapsulation is your only option there. — Martijn Pieters
– Martijn Pieters, Commented May 22, 2015 at 16:23

jatal · Accepted Answer · 2015-05-22 16:52:38Z

2

One option would be to store each line in a Dict that included additional metadata. This is analogous to using Decorator pattern to add metadata field(s) to your type.

For example, suppose you had a test file like so:

$ cat test.file 
line_1
line_2

You could do something like the following to add metadata:

>>> with open('./test.file','rb') as fin:
...   for line in fin:
...     linecount += 1
...     d = {'line':line,'metadata':'a line %d' % linecount}
...     lines.append(d)
... 
>>> print(lines)
[{'line': 'line_1\n', 'metadata': 'a line 1'}, {'line': 'line_2\n', 'metadata': 'a line 2'}]

answered May 22, 2015 at 16:52

jatal

8602 gold badges11 silver badges21 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Aktaeon Over a year ago

Yes, this is similar as laike9m suggestion. I guess this is the solution if I don't want to add a new class. Thanks.

Jean-François Fabre · Accepted Answer · 2019-05-07 14:00:44Z

1

You should define a MyArray class and delegates everything to array.array. So what do you think of this even simpler solution?

id = "your_id"
array = array.array('f', [...])
data = {id: array}

edited May 7, 2019 at 14:00

Jean-François Fabre♦

141k24 gold badges179 silver badges246 bronze badges

answered May 22, 2015 at 16:50

laike9m

19.6k23 gold badges117 silver badges154 bronze badges

3 Comments

Aktaeon Over a year ago

I am not refusing to define a new class, I was merely asking if there was a dynamic way to add attributes to an existing class. Your suggestion is an option though.

laike9m Over a year ago

In general, you can add new attr to an existing class/instance, but not array.array. If you modify the built-in objects like array, it may not behave what it should be then do you harm, so Python prevent people from doing this.

Aktaeon Over a year ago

Yes this is what I noticed when I tried adding a new function to the class. I guess it makes sense. I will wait a bit for other suggestions and benchmark the impact but I will probably go for this solution. Not exactly what I wanted but it seems to be the only way.

Collectives™ on Stack Overflow

Adding metadata to existing python objects

2 Answers 2

1 Comment

3 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

3 Comments

Your Answer

Sign up or log in

Post as a guest

Related