The semantics are a bit subtle. This is almost always used to separate the portion of code which should be executed from the portions of code which define functionality. So Python code often contains a line like:
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Why use def main()? [duplicate] Ask Question. up vote down vote favorite. It will be possible to import that python code as a module without nasty side-effects. I myself usually start writing small throwaway scripts without any kind of function. If the script grows big enough, or if I feel putting all that code inside a. A module allows you to logically organize your Python code. Grouping related code into a module makes the code easier to understand and use. A module is a Python object with arbitrarily named attributes that you can bind and reference. Simply, a module is a file consisting of Python code. A module. The if __name__ construct will let you easily re-use the functions and classes in the module in other Python scripts. If you don't do that, then everything in the module will run when it is import ed.
It helps us to modularize our code by breaking a program into logical parts where each part is responsible for a specific task. For example, in one of our first programs there was a function called drawSquare that was responsible for having some turtle draw a square of some size.
The actual turtle and the actual size of the square were defined to be provided as parameters. Here is that original program. Screen Set up the window and its attributes wn. Turtle create alex drawSquare alex, 50 Call the function to draw the square wn. Next, we define the function drawSquare.
At this point, we could have defined as many functions as were needed. Finally, there are five statements that set up the window, create the turtle, perform the function invocation, and wait for a user click to terminate the program.
These final five statements perform the main processing that the program will do. Notice that much of the detail has been pushed inside the drawSquare function. However, there are still these five lines of code that are needed to get things done. In many programming languages e. They are required to be part of a special function that is automatically invoked by the operating system when the program is executed.
This special function is called main. Although this is not required by the Python programming language, it is actually a good idea that we can incorporate into the logical structure of our program. In other words, these five lines are logically related to one another in that they provide the main tasks that the program will perform.
Since functions are designed to allow us to break up a program into logical pieces, it makes sense to call this piece main.
The following activecode shows this idea. The five lines of main processing are now placed inside this function. Finally, in order to execute that main processing code, we need to invoke the main function line When you push run, you will see that the program works the same as it did before.
First, import any modules that will be required.When Python interpreter reads a source file, it will execute all the code found in it. When Python runs the "source file" as the main program, it sets the special variable (__name__) to have a value ("__main__"). When you execute the main function, it will then read the "if" statement and checks whether __name__ does equal to __main__.
In contrast, when a module is imported into another module (or is imported in the python REPL), the value in the __name__ attribute is the name of the module itself (i.e. the name of the python file/script in which it is implicitly declared).
Summary For Python programmers, I've got some suggestions on how to write a main() function that's easy to invoke in other contexts, e.g. from the interactive Python prompt when you feel like experimenting.
A module can discover whether or not it is running in the main scope by checking its own __name__, which allows a common idiom for conditionally executing code in a module when it is run as a script or with python -m but not when it is imported.
The if __name__ construct will let you easily re-use the functions and classes in the module in other Python scripts.
If you don't do that, then everything in the module will run when it is import ed. Python modules lausannecongress2018.com files that consist of Python code. Any Python file can be referenced as a module.
Writing a module is just like writing any other Python file. Modules can contain definitions of functions, classes, and variables that can then be utilized in other Python programs.
If we run the.