Python os.dup2() Method



The method dup2() duplicates file descriptor fd to fd2, closing the latter first if necessary.

Note − New file description would be assigned only when it is available. In the following example given below, 1000 would be assigned as a duplicate fd in case when 1000 is available.


Following is the syntax for dup2() method −

os.dup2(fd, fd2);


  • fd − This is File descriptor to be duplicated.

  • fd2 − This is Duplicate file descriptor.

Return Value

This method returns a duplicate of file descriptor.


The following example shows the usage of dup2() method.


import os, sys

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

# Write one string
os.write(fd, "This is test")

# Now duplicate this file descriptor as 1000
fd2 = 1000
os.dup2(fd, fd2);

# Now read this file from the beginning using fd2.
os.lseek(fd2, 0, 0)
str =, 100)
print "Read String is : ", str

# Close opened file
os.close( fd )

print "Closed the file successfully!!"

When we run above program, it produces following result −

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