root@vsi:/mnt/d/ctf/pervaki/pwn7/mc# ipython
Python 3.8.0 (default, Oct 28 2019, 16:14:01) 
Type 'copyright', 'credits' or 'license' for more information
IPython 7.13.0 -- An enhanced Interactive Python. Type '?' for help.

In [1]: import struct

In [2]: struct.pack('d', 345.678)
Out[2]: b'\x02+\x87\x16\xd9\x9au@'

In [3]: struct.pack('d', 345.678).hex()
Out[3]: '022b8716d99a7540'

In [4]: struct.pack('d', 1000).hex()
Out[4]: '0000000000408f40'

In [5]: struct.unpack('d', b'\x00\x00\x00\x00\x00\x40\x8f\x40')
Out[5]: (1000.0,)

In [6]: struct.unpack('d', b'ololokek')
Out[6]: (2.2005931559457482e+209,)

In [7]: struct.pack('d', 2.2005931559457482e+209)
Out[7]: b'ololokek'

In [8]:                                                                                        
Do you really want to exit ([y]/n)? 
root@vsi:/mnt/d/ctf/pervaki/pwn7/mc# cat > test.c
#include <stdio.h>
int main() {
  double d;
  d = 2.2005931559457482e+209;
  printf("%s\n", (char*)&d);
}
root@vsi:/mnt/d/ctf/pervaki/pwn7/mc# gcc -o test test.c
root@vsi:/mnt/d/ctf/pervaki/pwn7/mc# ./test
ololokek