I find particularly difficult reading binary file with Python. Can you give me a hand? I need to read this file, which in Fortran 90 is easily read by
int*4 n_particles, n_groups real*4 group_id(n_particles) read (*) n_particles, n_groups read (*) (group_id(j),j=1,n_particles)
In detail, the file format is:
Bytes 1-4 -- The integer 8. Bytes 5-8 -- The number of particles, N. Bytes 9-12 -- The number of groups. Bytes 13-16 -- The integer 8. Bytes 17-20 -- The integer 4*N. Next many bytes -- The group ID numbers for all the particles. Last 4 bytes -- The integer 4*N.
How can I read this with Python? I tried everything but it never worked. Is there any chance I might use a f90 program in python, reading this binary file and then save the data that I need to use?
Read the binary file content like this:
with open(fileName, mode='rb') as file: # b is important -> binary fileContent = file.read()
then "unpack" binary data using struct.unpack:
The start bytes:
The body: ignore the heading bytes and the trailing byte (= 24); The remaining part forms the body, to know the number of bytes in the body do an integer division by 4; The obtained quotient is multiplied by the string
'i' to create the correct format for the unpack method:
struct.unpack("i" * ((len(fileContent) -24) // 4), fileContent[20:-4])
The end byte: