Read list of lists of tuples in Python from file

Question

I'd like to read and write a list of lists of tuples from and to files.

g_faces = [[(3,2)(3,5)],[(2,4)(1,3)(1,3)],[(1,2),(3,4),(6,7)]]

I used

pickle.dump(g_faces, fp)
pickle.load(fp)

But the file is not human readable. Is there an easy way to do it?

*"the file is not human readable"* - so what? It's not supposed to be. — jonrsharpe, Oct 16 '16 at 20:11
you could use `json` which uses the same interface or `eval` if you're brave. You'll have to compromise on the format a bit if you're using `json`. — Reut Sharabani, Oct 16 '16 at 20:11
Possibly a duplicate of [Python human readable object serialization](http://stackoverflow.com/questions/408866/python-human-readable-object-serialization?rq=1) — Tammo Heeren, Oct 16 '16 at 20:36

Tammo Heeren · Accepted Answer · 2016-10-16T20:48:38.437

1

Try the json module.

import json

g_faces = [[(3,2), (3,5)],[(2,4), (1,3), (1,3)],[(1,2), (3,4), (6,7)]]

json.dump(g_faces, open('test.json', 'w'))

g_faces = json.load(open('test.json'))

# cast back to tuples
g_faces = [[tuple(l) for l in L] for L in g_faces]

edited Oct 16 '16 at 20:48

answered Oct 16 '16 at 20:11

Tammo Heeren

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Note that JSON can't distinguish between lists and tuples (both are serialized as a JSON array), so the result will contain *all* lists. – jonrsharpe Oct 16 '16 at 20:12
@jonrsharpe Good point. The OP is asking for a list of tuples. – Tammo Heeren Oct 16 '16 at 20:16
It tells me: TypeError: <_io.TextIOWrapper name='test.json' mode='w' encoding='cp1252'> is not JSON serializable – Mario Stefanutti Oct 16 '16 at 20:25
@MarioStefanutti I swapped the order of argument in the `dump` method. Code has been corrected. – Tammo Heeren Oct 16 '16 at 20:28
Is there a way to make it read the inner elements as tuples instead of lists? – Mario Stefanutti Oct 16 '16 at 20:43
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@MarioStefanutti You could cast it into a tuple after you read it. As noted above, `json` will always cast the tuples as lists. – Tammo Heeren Oct 16 '16 at 20:46
Thanks. It works. I'm going to do like this. But do you know why JSON can't distinguish between lists and tuples. Is there a reason or limitation? – Mario Stefanutti Oct 16 '16 at 21:45
@MarioStefanutti Likely because JSON is used to move data between systems and languages. Not all languages implement tuples. My guess. – Tammo Heeren Oct 16 '16 at 21:47

Read list of lists of tuples in Python from file

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