What does <if __name__==&ldquo;__main__&rdquo;:> do?

# Threading example
import time, thread

def myfunction(string,sleeptime,lock,*args):
    while 1:
        lock.acquire()
        time.sleep(sleeptime)
        lock.release()
        time.sleep(sleeptime)
if __name__=="__main__":
    lock=thread.allocate_lock()
    thread.start_new_thread(myfunction, ("Thread #: 1", 2, lock))
    thread.start_new_thread(myfunction, ("Thread #: 2", 2, lock))

python threading_example.py

python myscript.py

if __name__ == "__main__":
    ...

# file one.py
def func():
    print("func() in one.py")

print("top-level in one.py")

if __name__ == "__main__":
    print("one.py is being run directly")
else:
    print("one.py is being imported into another module")

# file two.py
import one

print("top-level in two.py")
one.func()

if __name__ == "__main__":
    print("two.py is being run directly")
else:
    print("two.py is being imported into another module")

python one.py

top-level in one.py
one.py is being run directly

python two.py

top-level in one.py
one.py is being imported into another module
top-level in two.py
func() in one.py
two.py is being run directly

def printStuff(*args):
    for arg in args:
    	print arg

printStuff(1, 2, "Hello World")

1
2
Hello World

args = [4, 5, "Goodbye"]
printStuff(2, 3, *args)

2
3
4
5
Goodbye

# a.py
import b

# b.py
print "Hello World from %s!" % __name__

if __name__ == '__main__':
    print "Hello World from %s!" % __name__

$ python a.py
Hello World from b!

$ python b.py
Hello World from __main__!
Hello World from __main__!

def on_the_menu(arg, *args, **kwargs):
       print arg
       print args
       print kwargs

  >>> on_the_menu(5, "spam", "eggs", "ham", sausage="and spam", spam="plenty")
  5
  ('spam', 'eggs', 'ham')
  {'sausage': 'and spam', 'spam': 'plenty'}