python write c struct to file

binaryfile.py

from ctypes import *
import time
import datetime


class Record(Structure):
    _fields_ = [
        ("time", c_double),
        ("count", c_double)
    ]

    def __str__(self):
        return f"time:{self.time2obj()}\tcount:{self.count}"

    def time2obj(self):
        return datetime.datetime.fromtimestamp(self.time)


class BinaryFile(object):
    def __init__(self, name, T):
        self.T = T
        self.Tsize = sizeof(T)
        self._f = open(name, "ab+")

    def close(self):
        self._f.close()

    def write(self, **args):
        return self._f.write(bytearray(self.T(**args)))

    def _read(self, size):
        return self._f.read(size)

    def readn(self,n=1):
        buffer = self._read(self.Tsize * n)
        newT = self.T * n
        return newT.from_buffer_copy(buffer)
    
    def seek(self, offset, whence):
        return self._f.seek(offset, whence)

    def tell(self):
        return self._f.tell()

    def readfull(self):
        self.seek(0,2)
        fsize = self.tell()
        n = int(fsize / self.Tsize)
        self.seek(0,0)
        return self.readn(n)
    
    def readlast(self):
        self.seek(0,2)
        fsize = self.tell()
        if fsize < self.Tsize:
            return None
        self.seek(fsize-self.Tsize, 0)
        return self.readn()

if __name__ == "__main__":
    bf = BinaryFile("test.bin", Record)
    record = bf.readlast()
    t, count = time.time(), 1
    if record is not None:
        count = record[0].count + 1
    for _ in range(10):
        bf.write(time=t, count=count)
        time.sleep(0.01)
        t = time.time()
        count += 1
    
    rows = bf.readfull()
    for i in rows:
        print(i)