Splitting tuples in Python - best practice?

Question

I have a method in my Python code that returns a tuple - a row from a SQL query. Let's say it has three fields: (jobId, label, username)

For ease of passing it around between functions, I've been passing the entire tuple as a variable called 'job'. Eventually, however, I want to get at the bits, so I've been using code like this: (jobId, label, username) = job

I've realised, however, that this is a maintenance nightmare, because now I can never add new fields to the result set without breaking all of my existing code. How should I have written this?

Here are my two best guesses: (jobId, label, username) = (job[0], job[1], job[2]) ...but that doesn't scale nicely when you have 15...20 fields

or to convert the results from the SQL query to a dictionary straight away and pass that around (I don't have control over the fact that it starts life as a tuple, that's fixed for me)

Answer 1

@Staale

There is a better way:

job = dict(zip(keys, values))

Answer 2

I'd say that a dictionary is definitely the best way to do it. It's easily extensible, allows you to give each value a sensible name, and Python has a lot of built-in language features for using and manipulating dictionaries. If you need to add more fields later, all you need to change is the code that converts the tuple to a dictionary and the code that actually makes use of the new values.

For example:

job={}
job['jobid'], job['label'], job['username']=<querycode>

Answer 3

This is an old question, but...

I'd suggest using a named tuple in this situation: collections.namedtuple

This is the part, in particular, that you'd find useful:

Subclassing is not useful for adding new, stored fields. Instead, simply create a new named tuple type from the _fields attribute.

Answer 4

Perhaps this is overkill for your case, but I would be tempted to create a "Job" class that takes the tuple as its constructor argument and has respective properties on it. I'd then pass instances of this class around instead.