Python in a Nutshell

Name

qsize

Synopsis

                     q.qsize( )

Returns the number of items that are currently in q.

Queue offers a good example of the idiom “it’s easier to ask forgiveness than permission” (EAFP), covered in Chapter 6. Due to multithreading, each non-mutating method of q can only be advisory. When some other thread executes and mutates q, things can change between the instant a thread gets the information and the very next moment, when the thread acts on the information. Relying on the “look before you leap” (LBYL) idiom is futile, and fiddling with locks to try and fix things is a substantial waste of effort. Just avoid LBYL code such as:

if q.empty( ): print "no work to perform"
else: x=q.get_nowait( )

and instead use the simpler and more robust EAFP approach:

try: x=q.get_nowait( )
except Queue.Empty: print "no work to perform"