Welcome back, and this is our module four repetition, another flow control mechanism. And so far we have learned many things about python. As a review, we learned input, output, we learned the variables and operations. We learned the branching as one important type of flow control, and this time we're going to learn repetition, which is another super important flow control mechanism. So the repetition a lot of times, because we have to run programs repeatedly, and we cannot write the same code multiple times. It is not just about time consuming, but also it is hard to debug, it is hard to update or modify your code. If you write the same code again and again, when you have to do modification, you have to modify every piece of code even though you just write them once. We have to update multiple times, it will be easy to make mistakes. So repetition is very important, and we are going to set a repetition flow control, to run the same bunch of codes or statements multiple times. So that we achieve the purpose of we can do the same thing again and again, without have to write the same code, again and again. So in our previous labs, if we want to run a program multiple times, for example to enter a number, get some result. Internet temperature, getting some condition, we have to run a program multiple times. If we want to check three times, I mean at this time you may want to just copy the same code and the pace is three times. So you will get three times inter opportunity, and give the program run three times. But again, that is really time consuming and easy to make a mistake. So we need a repetition flow control to execute the same statements. And we have two ways for approach approaches, to control how we can repeat the same code. One is condition, as long as the condition is satisfied, we're going to continue to do the same thing again and again. So it's like we do something until the condition is not true anymore. The other one is count, to rather than take a condition which is a state, a very simple condition, that is whether or not we have repeat the same code the number of times we want. For example, if we want to run the program three times, then because we know the three as a magic number, then that will be a count based repetition, super easy. If we say whenever the temperature is below, let's say, below below 64 Fahrenheit. We are going to keep running the heat, so we won't feel cold, right? So that will be a condition based repetition, because we really don't know how many times we have to run the heat. Only when we know the condition or the temperature is above a certain threshold, we can stop the heat. So that will be the condition based repetition. We're going to learn these two in this module.