Write a list of Complex Numbers as Binary Data

Question

I'm trying to output some data from a python script to a binary file.

If I have a list of floats I've been using this

out_file = open("filename", "wb")
float_array.array("f", [])
float_array.fromlist(mylist)
float_array.tofile(out_file)
out_file.close()

This seems to work fine, at least it's resulting in a file with the correct number of bytes.

How can I do the same thing but using a list of complex numbers?

Thanks

For complex numbers there is no standard binary representation (at least that I am aware of), so you will first have to decide how you want them represented. — Björn Pollex
– Björn Pollex, Commented May 17, 2011 at 9:52
I would be happy to have them as a list of doubles or floats. It doesn't really matter as long as I can read them back. — rvabdn
– rvabdn, Commented May 17, 2011 at 10:26

Eli Bendersky · Accepted Answer · 2011-05-17 09:56:43Z

2

Don't invent your own serialization methods when Python offers so many good ones out of the box! I suggest you use pickle - it works with complex numbers as well (*):

>>> import pickle
>>> s = pickle.dumps([1+2j, 5-1j])
>>> pickle.loads(s)
[(1+2j), (5-1j)]

I'm using dumps for demonstration here, you can also use dump which writes to a binary file.

(*) From the doc of pickle:

The following types can be pickled:

None, True, and False

integers, long integers, floating point numbers, complex numbers

normal and Unicode strings

tuples, lists, sets, and dictionaries containing only picklable objects

functions defined at the top level of a module

built-in functions defined at the top level of a module

classes that are defined at the top level of a module

instances of such classes whose __dict__ or __setstate__() is picklable (see section The pickle * protocol for details)

answered May 17, 2011 at 9:56

Eli Bendersky

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3 Comments

Jakob Bowyer Over a year ago

Remember dumping when writing a pickle file to use binary mode ;)

rvabdn Over a year ago

Thanks, I'm not sure if this is going to work. It seems to be writing a lot more data than I expect. I need to be able to read this data from C code so I need raw binary data.

Eli Bendersky Over a year ago

@rvabdn: Python's cPickle is implemented in C, you could probably get it to work from C code. Maybe this is all too complex for your needs, but I'm just leaving it as a suggestion

MartinStettner · Accepted Answer · 2011-05-17 09:58:23Z

1

You could create a flattened list of floats out of your complex array like

flattend = [f for sublist in ((c.real, c.imag) for c in complex_list) for f in sublist]

and write this one to the file.

answered May 17, 2011 at 9:58

MartinStettner

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1 Comment

rvabdn Over a year ago

This is the route I went in the end.

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