如何用Python将变量写成二进制数据？

Question

I need to write a long list of ints and floats with Python the same way fwrite would do in C - in a binary form.

This is necessary to create input files for another piece of code I am working with.

What is the best way to do this?

Answer 1

You can do this quite simply with the struct module.

For example, to write a list of 32-bit integers in binary:

import struct

ints = [10,50,100,2500,256]
with open('output', 'w') as fh:
    data = struct.pack('i' * len(ints), *ints)
    fh.write(data)

Will write '\\n\\x00\\x00\\x002\\x00\\x00\\x00d\\x00\\x00\\x00\\xc4\\t\\x00\\x00\\x00\\x01\\x00\\x00'

Answer 2

Have a look at numpy: numpy tofile :

With the array-method 'tofile' you can write binary-data:

# define output-format
numdtype = num.dtype('2f')

# write data
myarray.tofile('filename', numdtype)

Another way is to use memmaps: numpy memmaps

# create memmap                                              
data = num.memmap('filename', mode='w+', dtype=num.float, offset=myoffset, shape=(my_shape), order='C')
# put some data into in:
data[1:10] = num.random.rand(9)
# flush to disk:
data.flush()
del data