How to create a nested data structure in Python?

Question

Since I recently started a new project, I'm stuck in the "think before you code" phase. I've always done basic coding, but I really think I now need to carefully plan how I should organize the results that are produced by my script.

It's essentially quite simple: I have a bunch of satellite data I'm extracting from Google Earth Engine, including different sensors, different acquisition modes, etc. What I would like to do is to loop through a list of "sensor-acquisition_mode" couples, request the data, do some more processing, and finally save it to a variable or file.

Suppose I have the following example:

sensors = ['landsat','sentinel1']
sentinel_modes = ['ASCENDING','DESCENDING']
sentinel_polarization = ['VV','VH']

In the end, I would like to have some sort of nested data structure that at the highest level has the elements 'landsat' and 'sentinel1'; under 'landsat' I would have a time and values matrix; under 'sentinel1' I would have the different modes and then as well the data matrices.

I've been thinking about lists, dictionaries or classes with attributes, but I really can't make up my mind, also since I don't have that much of experience. At this stage, a little help in the right direction would be much appreciated!

Pick either dictionaries (if you just need to hold values) or objects (if you need behaviour too), as keys/attributes are more readable than indices. Apart from that, just start writing something and see how it goes; you can always refactor if you need to. — jonrsharpe
– jonrsharpe, Commented Jun 22, 2016 at 14:49
I would also go with dictionary as the highest level. Also you get better ideas when you start coding than thinking abstractly. — Dataman
– Dataman, Commented Jun 22, 2016 at 14:51
Agreed. In addition this site is a really great place to just sort of mess around with coding ideas via Python. Check out the docs too for further information. codeskulptor.org — terratunaz
– terratunaz, Commented Jun 22, 2016 at 14:51

Delioth · Accepted Answer · 2016-06-22 14:56:26Z

Lists: Don't use lists for nested and complex data structures. You're just shooting yourself in the foot- code you write will be specialized to the exact format you are using, and any changes or additions will be brutal to implement.
Dictionaries: Aren't bad- they'll nest nicely and you can use a dictionary whose value is a dictionary to hold named info about the keys. This is probably the easiest choice.
Classes: Classes are really really useful for this if you need a lot of behavior to go with them - you want the string of it to be represented a certain way, you want to be able to use primitive operators for some functionality, or you just want to make the code slightly more readable or reusable.

From there, it's all your choice- if you want to go through the extra code (it's good for you) of writing them as classes, do it! Otherwise, dictionaries will get you where you need to go. Notably the only thing a dictionary couldn't do would be if you have two things that should be at the key level in the dictionary with the same name (Dicts don't do repetition).

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