convert large integer to float in python

Question

an API that I cannot influence is saving certain floating point numbers as contiguousarray with 64 bit, so that a value of -0.30273306 is saved as -4624246862885421056.

Now how can I retrieve the original value from this large integer?

Olvin Roght · Accepted Answer · 2019-09-02 10:10:39Z

2

You can use struct module. Firstly we pack i as long long (8 bytes signed integer). Then we unpack it as double (8-byte floating point number).

import struct

i = -4624246862885421056
f = struct.unpack("d", struct.pack("q", i))

answered Sep 2, 2019 at 10:10

Olvin Roght

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5 Comments

CD86 Over a year ago

that looks cumbersome but thanks a lot =) does this also work for numpy arrays or just for single numbers?

Olvin Roght Over a year ago

@CarstenD, that's best option in my opinion. If you're reading this values from file, you can read them as double. About numpy arrays I don't clearly understand.

CD86 Over a year ago

how would I read the data as double? several of those numbers are stored as meta data in an hdf5 file and I need to access it by a key that returns an np.array which contains multiple numbers

Olvin Roght Over a year ago

@CarstenD, it's much more complicated question. I'm not familiar with this file format, so I can't help you using my own experience. If in codec you use to read this file there's some option to override reader, you can use it.

Olvin Roght Over a year ago

@CarstenD, about numpy array, I think there's an option how to apply same changes to all elements.

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