python struct unpack into a dict

Question

struct.unpack will unpack data into a tuple. Is there an equivalent that will store data into a dict instead?

In my particular problem, I am dealing with a fixed-width binary format. I want to be able, in one fell swoop, to unpack and store the values in a dict (currently I manually walk through the list and assign dict values)

I don't think so. But the `dict` constructor can take a list or iterator of (name, value) pairs to initialize with. That might help you. — Keith, Aug 23 '11 at 01:47
You might also be interested in `namedtuple` if you don't need to modify the object after creating it. — kindall, Aug 23 '11 at 01:56

score 11 · Answer 1 · answered Aug 23 '11 at 02:15

If you're on 2.6 or newer you can use namedtuple + struct.pack/unpack like this:

import collections
import struct

Point = collections.namedtuple("Point", "x y z")

data = Point(x=1, y=2, z=3)

packed_data = struct.pack("hhh", *data)
data = Point(*struct.unpack("hhh", packed_data))

print data.x, data.y, data.z

score 9 · Answer 2 · answered Aug 23 '11 at 02:09

9

Do you want something like this?

keys = ['x', 'y', 'z']
values = struct.unpack('<III', data)
d = dict(zip(keys, values))

answered Aug 23 '11 at 02:09

FogleBird

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that's what im doing now. I was hoping for something a bit slicker – Foo Bah Aug 23 '11 at 02:12
its a list that is being walked through (unless zip does something clever that doesnt involve walking through the list). – Foo Bah Aug 23 '11 at 02:22
3

I feel this solution is fine, and already slicker than mucking around with `collections.namedtuple` – wim Aug 23 '11 at 03:59
just as an aside this method is **MUCH** faster than the named tuple version – Joran Beasley Dec 21 '19 at 21:45

score 6 · Accepted Answer · answered Aug 23 '11 at 02:23

6

The struct documentation shows an example of unpacking directly into a namedtuple. You can combine this with namedtuple._asdict() to get your one swell foop:

>>> import struct
>>> from collections import namedtuple
>>> record = 'raymond   \x32\x12\x08\x01\x08'
>>> Student = namedtuple('Student', 'name serialnum school gradelevel')
>>> Student._asdict(Student._make(struct.unpack('<10sHHb', record)))
{'school': 264, 'gradelevel': 8, 'name': 'raymond   ', 'serialnum': 4658}
>>>

If it matters, note that in Python 2.7 _asdict() returns an OrderedDict...

answered Aug 23 '11 at 02:23

mtrw

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Heh probably should have checked the web doc. No indication of this in the python `help(struct)` – Foo Bah Aug 23 '11 at 03:03
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interesting answer. i see it's a dynamically generated function, but why is _asdict() with a prepended underscore? – wim Aug 23 '11 at 03:58
Using private methods - great idea. – FogleBird Aug 24 '11 at 00:44
1

@FogleBird - not sure what you mean by private methods. `namedtuple._asdict()` is documented here: http://www.python.org/doc//current/library/collections.html#collections.somenamedtuple._asdict. And I took the usage of `namedtuple._make()` directly from the documentation linked in the answer. What's the recommended best practice here? – mtrw Aug 24 '11 at 01:38
The spaces after raymond makes me crazy to debug the code. – coanor Feb 06 '14 at 12:44
Why the code can not run under python3: `TypeError: 'str' does not support the buffer interface`? – coanor Feb 06 '14 at 12:49
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You can rewrite the fifth line more concisely as `Student(*struct.unpack('<10sHHb', record))._asdict()` – Alastair Irvine Nov 20 '18 at 09:22
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this solution is significantly slower than `dict(zip(keys,struct.unpack(...)))` – Joran Beasley Dec 21 '19 at 21:46

python struct unpack into a dict

3 Answers3