[0:00] what is going on guys welcome back in
[0:01] this video today we're going to cover
[0:03] multi-threading in python as simply and
[0:05] as quickly as possible so let us get
[0:07] right into it it's not a g it's
[0:12] [Music]
[0:16] AED all right now one thing that I want
[0:18] to mention right away is that there is
[0:20] no actual multi-threading in Python at
[0:22] least not in the most commonly used
[0:24] cpython implementation that you're
[0:25] probably running on your system because
[0:28] of something called the global interpret
[0:30] to lock and we're not going to go into
[0:31] too much detail here but what this
[0:33] essentially means is that we have some
[0:35] sort of pseudo multi-threading where we
[0:37] do stuff concurrently and somewhat at
[0:39] the same time but what's actually
[0:41] happening is that we're switching
[0:43] between the tasks and we're using the
[0:44] down times of the different tasks to
[0:46] execute the other tasks so for example
[0:48] we send a request we wait for a response
[0:51] that is some doubt time or we're waiting
[0:52] for user input that is some downtime or
[0:55] we're just sleeping with time dos sleep
[0:57] that is also some downtime and this can
[0:58] be used for execution of other tasks and
[1:01] this is what the threading module
[1:02] actually does and this is just the
[1:04] theoretical background here in order to
[1:06] work with multi-threading and python
[1:08] with the pseudo multi-threading in
[1:10] Python what you need to do is you need
[1:11] to say import threading uh this is a
[1:14] core python module we don't need to
[1:15] install anything for that uh and in
[1:18] addition to that we're going to also
[1:19] import time which is going to allow us
[1:21] to use the mentioned sleep function to
[1:23] create some downtime and we're going to
[1:26] do a very simple example here to
[1:27] understand the concept of threading in
[1:29] python or for multi-threading in Python
[1:31] what we're going to do is we're going to
[1:32] define a function we're going to call it
[1:34] worker because it's going to be our
[1:36] worker function and this function will
[1:38] do something quite simple we're going to
[1:40] Define a variable up here done we're
[1:42] going to set it to false and inside of
[1:45] our worker function we're going to have
[1:47] a loop while not done so basically an
[1:49] endless loop until this thing is set to
[1:52] True while not done we're going to say
[1:56] uh time do sleep wait 1 second sleep 1
[2:00] second basically and then we're going to
[2:03] print some counter we're going to first
[2:06] of all Define a counter up here being
[2:08] equal to zero we're going to say that
[2:11] the counter is going to be increased by
[2:12] one with each
[2:14] iteration and we're going to print the
[2:16] counter this is what we want to do here
[2:18] nothing too fancy just a simple function
[2:20] that constantly prints 1 2 3 4 until we
[2:24] set done to true so without using any
[2:27] threading stuff here let's just run this
[2:29] function and see what happens this is
[2:31] going to be then running in the main
[2:32] thread and you can see it just prints 1
[2:34] 2 3 4 5 and so on um now what we want to
[2:39] do here is we want to in addition to
[2:41] that function also process some user
[2:43] input so in the main thread for example
[2:45] we want to wait for the user to input
[2:47] something or to just press enter now how
[2:50] would we do that we would do something
[2:52] like while not
[2:53] done we want to say uh wait for the user
[2:57] input so press PR enter to quit for
[3:02] example or actually we don't need to
[3:04] Loop here we can just wait for the input
[3:05] statement here and after the input
[3:07] statement is over so after the user
[3:09] presses uh enter we can just set done to
[3:12] true so the goal is to have this
[3:14] function running counting from uh 1 to
[3:17] two to three to four and so on until we
[3:19] press enter to quit that the problem is
[3:22] however now that um this is running in
[3:25] the main thread and this comes after dys
[3:28] function so we will not get to that
[3:29] statement uh unless this function
[3:32] finishes with the work so unless this
[3:34] function breaks out of the loop and we
[3:35] can continue with the rest of the code
[3:37] if we want to have both things running
[3:39] simultaneously we will have to do
[3:41] multi-threading and this is done the
[3:43] following way we used the threading
[3:44] module to define a thread by saying
[3:46] threading do thread and then we can
[3:49] specify a Target function so Target
[3:51] equals and we can pass the worker
[3:53] function here as an object passing it as
[3:56] an object means not passing it with the
[3:57] parenthesis so not calling it but just
[4:00] uh passing the instance of worker just
[4:03] passing the object worker which is the
[4:05] function The Entity worker um and then
[4:09] this is the object this is the actual
[4:10] threat we can either store it in a
[4:12] variable and then start the variable or
[4:13] we can start it right away like this by
[4:16] setting saying threading do thread
[4:18] Target equals worker. start and this is
[4:20] going to now start the worker function
[4:22] in a separate thread so if I run this um
[4:25] you will be able to see press enter to
[4:27] quit 1 2 3 I'm not pressing anything if
[4:29] I now press enter it goes past the
[4:32] statement and it sets done to true and
[4:34] since done is set to true this also
[4:36] terminates this worker now this would
[4:39] not work of course if I have here an
[4:41] endless loop while true then even if I
[4:44] press enter it's not going to quit
[4:46] because then uh the main thread doesn't
[4:48] have anything to do but this threat is
[4:50] still running however we can also change
[4:53] that by saying that this threat is not
[4:55] an important threat we don't want to
[4:57] keep the program running if everything
[4:59] else has finished finished this is a
[5:00] so-called Damon threat which basically
[5:02] means if nothing else is running you can
[5:04] also quit the script even though this
[5:06] threat is running we can specify here
[5:08] Damon equals true and this basically
[5:11] means what I just said that this is
[5:12] running in the background and as soon as
[5:15] the main threat and the other important
[5:16] threats have finished we can also quit
[5:19] the script we don't have to wait for
[5:20] this particular threat here because it's
[5:23] just a Damon threat so I can run this
[5:24] now and I can press enter And even
[5:27] though this enter doesn't change
[5:29] anything about this Loop even though
[5:30] this threat is still running we're just
[5:32] terminating the whole script because
[5:33] this is just a Damon threat that is what
[5:36] this is for we can also pass arguments
[5:38] by just passing text here for example
[5:41] and saying that we want to print an F
[5:44] string with text and then the counter
[5:47] just making up some stuff here uh we can
[5:50] do that by passing arguments so we can
[5:52] say arcs equals and we can pass a tupal
[5:55] of arguments here and in this case we're
[5:56] going to just pass ABC but since this is
[5:58] a tupal we need need to also pass a
[6:00] comma otherwise this is just going to be
[6:02] treated as a single value but we need a
[6:04] tuple uh we can do the same thing we can
[6:06] run another thread with the same
[6:08] function XYZ here as a text and you're
[6:11] going to see what this actually does you
[6:14] can see that it uh prints ABC counter oh
[6:17] actually I just noticed that we're uh
[6:19] printing counter we need of course to
[6:21] print the actual value of counter you
[6:25] can see here now abc1 xyz1 uh how these
[6:28] are running in parallel and if I press
[6:30] enter since both of them are Damon
[6:32] threats we are quitting the script if I
[6:34] set now one of them not to a Damon
[6:36] threat and the other one uh to a Damon
[6:38] threat uh you will see that if I just
[6:40] press enter now one of them is going to
[6:42] stop um
[6:45] actually doesn't stop any of those oh of
[6:48] course sorry this was uh this was not a
[6:50] correct thought because since one of
[6:52] them is running the other one is going
[6:53] to run as well because if we set one of
[6:56] them to not a Damon thread this is still
[6:58] an important thread and because the
[7:00] script is not finished because there is
[7:02] some threat still running the Damon
[7:03] threat is going to run as well um so
[7:06] setting one of them to false to not
[7:09] being a Damon threat keeps all of them
[7:10] running because Damon doesn't mean that
[7:12] you're just quitting it but it just
[7:14] means that since something is still
[7:16] running we're going to keep this running
[7:18] as well but if nothing else is running
[7:19] we're going to uh not keep this running
[7:22] anymore and the last thing I want to
[7:24] show you here I'm not going to show you
[7:25] here as a demonstration but just as a
[7:27] concept is if you have a list of mult
[7:29] multiple threats if you say for example
[7:31] this is T1 and this is T2 and you don't
[7:34] call the start but you just save them as
[7:36] objects here and then you do T1 start
[7:39] and T2 start this is the same
[7:41] functionality here you can also wait for
[7:43] those threats so if you do something and
[7:45] you don't want to continue with this
[7:47] here until both threats have finished
[7:49] with the execution then you can say t1.
[7:52] jooin and t2. jooin and you would not
[7:55] get to this code section here um until
[7:58] the threats have finished so you can see
[7:59] it doesn't even print press enter to
[8:01] quit because it doesn't get to that line
[8:03] since both threats are still running so
[8:06] that's it for today's video I hope you
[8:07] enjoyed it and hope you learned
[8:09] something if so let me know by hitting a
[8:10] like button and leaving a comment in the
[8:12] comment section down below and of course
[8:13] don't forget to subscribe to this
[8:14] Channel and hit the notification Bell to
[8:16] not miss a single future video for free
[8:18] other than that thank you much for
[8:19] watching see you in the next video and
[8:21] bye
[8:35] [Music]