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I am trying to read in a binary file in Python. The file consists of a thousands of lines each 2957 bytes long (1 byte boolean followed by 739 4 byte integers)

I have tried this suggestion but this does not work (the program runs forever)

This is my current setup, but I am having troubles iterating over the file:

with open("bin-file", "rb") as f:
for line in f:
    # Here I deal with every line

The problem is that every line in the loop is a different length, and the number of lines does not correspond to the actual number of lines in the file. I am assuming Python finds, what it thinks are, end-of-line markers in the binary data, but those do not correspond to the actual ends of the lines.

Another option I tried involves the struct.unpack() function to unpack line by line, since I know exactly how many bytes are on every line. 

import struct
unpack_str = '=?iiiiiiii...' # The actual string contains 739 i's
n_bytes = 2957 # There are 2957 bytes per line

with open("bin-file", "rb") as f:
    line_bin = f.read(n_bytes) 
    line_str = struct.unpack(unpack_str,line_bin)

This works, but only returns the first line. How would I iterate through all of the lines until I hit the EOF, knowing that every line is exactly n_bytes long?

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samuelschaefer
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  • My answer there includes reading binary files in exact chunks. – Martijn Pieters Oct 31 '14 at 20:06
  • As a side comment, your unpack string could be "B739i". And your second block is almost done. Just put it in a "while True" loop and have a test to verify "2957 == len(line_bin)" – Fred S Oct 31 '14 at 23:58

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