How to save 2D arrays (lists) in Python?

Question

I need to save a 2D array representing a map in the game world to a configparser. The data looks like this:

[[0, 0, 0, 0, 0], [0, 1, 1, 1, 0], [0, 0, 0, 0, 0]]

As an example.

I can obviously save the data but I can't convert it from a string back to a list after reading it back in...

I don't mind if I have to use a .txt file instead, by the way, and just read it in with the normal text file handler.

Answer 1

Python has a module for saving Python data called pickle . You can use that. From the docs:

The pickle module implements a fundamental, but powerful algorithm for serializing and de-serializing a Python object structure. “Pickling” is the process whereby a Python object hierarchy is converted into a byte stream, and “unpickling” is the inverse operation, whereby a byte stream is converted back into an object hierarchy. Pickling (and unpickling) is alternatively known as “serialization”, “marshalling,” 1 or “flattening”, however, to avoid confusion, the terms used here are “pickling” and “unpickling”.

Demo:

>>> import pickle
>>> data = [[0, 0, 0, 0, 0], [0, 1, 1, 1, 0], [0, 0, 0, 0, 0]]
>>> with open('C:/temp/pickle_test.data', 'w') as f:
    pickle.dump(data, f)


>>> with open('C:/temp/pickle_test.data', 'r') as f:
    new_data = pickle.load(f)


>>> new_data
[[0, 0, 0, 0, 0], [0, 1, 1, 1, 0], [0, 0, 0, 0, 0]]

Answer 2

You can do it using a simple eval

>>> x="[[0, 0, 0, 0, 0], [0, 1, 1, 1, 0], [0, 0, 0, 0, 0]]"
>>> type(x);
<type 'str'>
>>> y=eval(x);
>>> print(y);
[[0, 0, 0, 0, 0], [0, 1, 1, 1, 0], [0, 0, 0, 0, 0]]
>>>type(y);
<type 'list'>

It's a very quick and dirty solution, you should use more secure and good input files parsers (like pickle).

Answer 3

For the transformation of a string to a list you could do something like this:

myList = [x for x in "0,1,2,3".split(",")]
type(myList)
<type 'list'>
print myList
['0', '1', '2', '3']