os.fsync(fd)

import os, sys
# Open a file
fd = os.open( "foo.txt", os.O_RDWR|os.O_CREAT )

# Write one string
line="this is test"
b=line.encode()
os.write(fd, b)

# Now you can use fsync() method.
# Infact here you would not be able to see its effect.
os.fsync(fd)

# Now read this file from the beginning
os.lseek(fd, 0, 0)
line = os.read(fd, 100)
b=line.decode()
print ("Read String is : ", b)

# Close opened file
os.close( fd )
print ("Closed the file successfully!!")

Read String is : this is test
Closed the file successfully!!