Python Tutorial - 15. if __name__ == "__main__"

Key Takeaways

hello and welcome to code Basics coding tutorial today we are going to talk about very interesting topic if you have looked at python programs uh you might have noticed this line and this is very common in any Python program let's see what this is it is saying if undor unor name equal toore main let's first check out what is underscore uncore name if you have idle open let me open idle first we will see what is the value of underscore uncore name when I do this it is telling me the value of this particular variable is mean so this is a predefined variable in Python which is which gets set to mean if you run here for example if if you run area. py directly then this will be set as mean so let's just run it you see it is now calculating the area Okay so this thing is used as kind of like an entry point for any Python program now if you have done any coding in C or Java uh the entry point in those programming languages is main function as shown here so if you recall call if you're in C Java this is the function from where your program execution begins that's why it is called an entry point similarly in Python this thing is often used as an entry point inside the program okay now when does the value of underscore uncore name is something other than main well if you have another file called caller. py where you are importing area module so you are importing area meaning you are importing all the code in area. py file which is here and I'm saying I'm in color. py and you're calculating the area okay now if you're in here in area I'm just going to print uh the value of the name okay so underscore underscore let's see what is the value of underscore name when we call it from caller. py okay so I'm saying I am in caller. py let me add one more line here saying that I am in area. py Okay and first I will execute area py and call. py and we will see the difference uh of this print statement okay now this time I'm going to execute it in a little different way usually I run it from py Cham uh editor itself but today I'm going to show you how you can run any python file using Windows command prompt okay I have Windows command prompt open here and I am in the directory where I have area. py and color. piy okay now if I if I want to execute uh area. py directly then this is how I will execute it I will say python area. py so python is my interpreter and I'm executing area. py when I say this I get I am in area. py and the value of underscore name isore main okay let's see what happens if you execute caller. p Y when you do that it is saying that I'm in caller. py but the underscore name value is now area so if you compare that with here it begin execution of this program and that's why it printed I'm in caller. py here and from here it went into another file which is area so it went in here and when it started executing calcul Cal area the value of underscore uncore name was area so the summary here is when you execute python area. py directly the value of underscore uncore name is Main and when you execute it from some other file the value of that variable is the name of that module here we are treating area. py as a module okay so that was all all about uh uncore uncore name thanks for watching