Matlab to Python Conversion binary file read

Question

I am new to both Matlab and Python and I have to convert a program in Matlab to Python. I am not sure how to typecast the data after reading from the file in Python. The file used is a binary file.

Below is the Matlab code:

fid = fopen (filename, 'r');
 fseek (fid, 0, -1);
 meta = zeros (n, 9, 'single');
 v = zeros (n, 128, 'single');
 d = 0;
 for i = 1:n
   meta(i,:) = fread (fid, 9, 'float');
   d = fread (fid, 1, 'int');
   v(i,:) = fread (fid, d, 'uint8=>single');
 end

I have written the below program in python:

fid = open(filename, 'r')
fid.seek(0 , 0)
meta = np.zeros((n,9),dtype = np.float32)
v = np.zeros((n,128),dtype = np.float32)

for i in range(n):
  data_str = fid.read(9);
  meta[1,:] = unpack('f', data_str)

For this unpack, I getting the error as

"unpack requires a string argument of length 4"

. Please suggest someway to make it work.

You should check out this thread: stackoverflow.com/questions/3162191/…. Not necessarily hard, but quite a challege for a beginner in both languages. — jake77
– jake77, Commented Oct 24, 2015 at 15:35

jake77 · Accepted Answer · 2015-10-24 16:20:25Z

0

I looked a little in the problem mainly because I need this in the near future, too. Turns out there is a very simple solution using numpy, assuming you have a matlab matrix stored like I do.

import numpy as np

def read_matrix(file_name):
    return np.fromfile(file_name, dtype='<f')  # little-endian single precision float

arr = read_matrix(file_path)

print arr[0:10]  #sample data
print len(arr)  # number of elements

The data type (dtype) you must find out yourself. Help on this is here. I used fwrite(fid,value,'single'); to store the data in matlab, if you have the same, the code above will work. Note, that the returned variable is a list; you'll have to format it to match the original shape of your data, in my case len(arr) is 307200 from a matrix of the size 15360 x 20.

answered Oct 24, 2015 at 16:20

jake77

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