Blocking Functions
The following functions can cause the current thread to block (i.e. can take seconds or minutes to complete):
Network-related
The following operations can block, because they need to look up a hostname, or retrieve a remote resource. To do non-blocking retrievals, use select.select or socket.setblocking(0).
socket.accept socket.close socket.connect socket.getfqdn socket.getaddrinfo socket.gethostbyname socket.gethostbyaddr socket.getnameinfo socket.getnameinfo_ex socket.recv socket.recv_into socket.recvfrom socket.recvfrom_into socket.send socket.sendall socket.sendto urllib.urlopen urllib.urlretrieve
File-related
The following operations can block, because disk-access can be slow or even across a network. Even writing to stdin/stdout/stderr can block, or reads from another process. Arno says: these should be safe to use as long as your not on a network file system. If we can't use these, things get complicated ;o)
file.close file.flush file.open file.read file.readlines file.truncate file.write file.writelines file.xreadlines os.access os.chdir os.chmod os.chown os.close os.fchdir os.fdopen os.fstat os.fstatvfs os.fsync os.ftruncate os.listdir os.lstat os.makedirs os.mkdir os.mkfifo os.mknod os.open os.read os.readlink os.remove os.removedirs os.rename os.renames os.rmdir os.stat os.stat_float_times os.statvfs os.symlink os.tempnam os.tmpfile os.tmpnam os.walk os.write
Process-related
The following commands can block because they wait for something to finish (for some, a timeout of zero can be used to avoid blocking):
os.system os.wait os.wait3 os.wait4 os.waitpid threading.Thread.join
Time-related
The following commands can block because they (can) wait for time to pass:
select.select time.sleep
Lock-related
The following commands can block because they need some (user-created) lock. Some of these can be explicitly set to non-blocking:
thread.allocate_lock.acquire threading.BoundedSemaphore.acquire threading.Condition.acquire threading.Condition.wait threading.Event.wait threading.Lock.acquire threading.RLock.acquire threading.Semaphore.acquire