python os.fork() 的返回值是多少？

Question

Python os.pipe() and os.fork() are new to me and I have a few basic questions about them. There is a code taken from here as follows:

# Python program to explain os.fork() method

# importing os module
import os


# Create a child process
# using os.fork() method
pid = os.fork()

# pid greater than 0 represents
# the parent process
if pid > 0 :
    print("I am parent process:")
    print("Process ID:", os.getpid())
    print("Child's process ID:", pid)

# pid equal to 0 represents
# the created child process
else :
    print("\nI am child process:")
    print("Process ID:", os.getpid())
    print("Parent's process ID:", os.getppid())


# If any error occurred while
# using os.fork() method
# OSError will be raised

and the output is:

I am Parent process
Process ID: 10793
Child's process ID: 10794

I am child process
Process ID: 10794
Parent's process ID: 10793

When I print out pid , two integers are displayed, one of which is always 0. According to the code comments, pid greater than 0 represents the parent process , if this is the case then why inside if pid > 0 block, which means pid value corresponds to the parent, there is print("Child's process ID:", pid) where the value of pid is associated with the child's process ID? Also, as pid returns two values how are they handled in both if and else statements as according to the output both if and else are executed?

Answer 1

According to the documentation: os.fork() return 0 in the child and the child's process id in the parent. If an error occurs OSError is raised.