command-line arguments or fetching data from standard input. When you execute a script, you will not be able to interactively define the code that the Python interpreter is executing. The execution of the code starts from the starting line and goes line by line. If youre new to Python modules, see the tutorial section My code is terminated without output when I remove the if. News difficulty : Medium. Main function is like the entry point of a program. the phrase variable would be global to the entire module. Now, the main function is like any other function in Python. Youll see the words file, module, and script used throughout this article. contains a collection of tutorials and references on how to distribute and The first string after the function is called the Document string or Docstring in short. A-143, 9th Floor, Sovereign Corporate Tower, We use cookies to ensure you have the best browsing experience on our website. // This main function to convert infix expression //to postfix expression function infixToPostfix(s) { . in the standard library. Scrapy Tutorial: How To Make A Web-Crawler Using Scrapy? for a __main__.py file within a package, because its __name__ Join us and get access to thousands of tutorials, hands-on video courses, and a community of expert Pythonistas: Whats your #1 takeaway or favorite thing you learned? Most often, you will see this recommended when youre using pip: python3 -m pip install package_name. Code within this block wont run unless the module is executed in the We have been learning the concepts of Object Oriented Programming and their advantages for a long time. Working with PDF files to Python - GeeksforGeeks Easily compile and run Python code online with our powerful Python compiler. This import style can be used when referencing modules within a Django ModelForm Create form from Models, Django CRUD (Create, Retrieve, Update, Delete) Function Based Views, Class Based Generic Views Django (Create, Retrieve, Update, Delete), Django ORM Inserting, Updating & Deleting Data, Django Basic App Model Makemigrations and Migrate, Connect MySQL database using MySQL-Connector Python, Installing MongoDB on Windows with Python, Create a database in MongoDB using Python, MongoDB python | Delete Data and Drop Collection. What is the difference between "main()" and "main(_)" in python? If you are not familiar with Python packages, see section Packages ", "The variable __name__ tells me which context this file is running in.". though. Creating a GUI using Tkinter is an easy task. A 101 Guide On The Least Squares Regression Method, Python Career Opportunities: Your Career Guide To Python Programming, Top Python developer Skills you need to know, Learn How To Make A Resume For A Python Developer. What is the Russian word for the color "teal"? With our online interpreter, you can test and debug your code in real-time, all from your web browser. (Source). If this file is being imported from another module, __name__ will be set to the modules name.__name__ is a built-in variable which evaluates to the name of the current module. My data read from the Web that has been modified, Importing Into a Module or the Interactive Interpreter, Use if __name__ == "__main__" to Control the Execution of Your Code, Create a Function Called main() to Contain the Code You Want to Run, Summary of Python Main Function Best Practices, Get a sample chapter from Python Tricks: The Book, Python Modules and Packages An Introduction, How to Publish an Open-Source Python Package to PyPI, Python import: Advanced Techniques and Tips, get answers to common questions in our support portal, What the best-practices are for what code to put into your, Running a computation that takes a long time, Printing information that would clutter the users terminal, Prints some output to tell the user that the data processing is starting, Pauses the execution for three seconds using, Prints some output to tell the user that the processing is finished, Reads a data file from a source that could be a database, a file on the disk, or a web API, Writes the processed data to another location, The name of the module, if the module is being imported. acknowledge that you have read and understood our, Data Structure & Algorithm Classes (Live), Data Structures & Algorithms in JavaScript, Data Structure & Algorithm-Self Paced(C++/JAVA), Full Stack Development with React & Node JS(Live), Android App Development with Kotlin(Live), Python Backend Development with Django(Live), DevOps Engineering - Planning to Production, GATE CS Original Papers and Official Keys, ISRO CS Original Papers and Official Keys, ISRO CS Syllabus for Scientist/Engineer Exam, Taking multiple inputs from user in Python. A variable created in the main body of the Python code is a global variable and belongs to the global scope. PyQt5 How to change background color of Main window ? Some modules contain code that is intended for script use only, like parsing Sometimes, when you are importing from a module, you would like to know whether a particular modules function is being used as an import, or if you are just using the original .py (Python script) file of that module. Now, you can run the whole processing pipeline from the command line, as shown below: In the output from this execution, you can see that the Python interpreter executed main(), which executed read_data_from_web(), process_data(), and write_data_to_database(). A Beginner's Guide to learn web scraping with python! named main encapsulates the programs primary behavior: Note that if the module didnt encapsulate code inside the main function we later package it as a console script entry-point in a pip-installable Here are four key best practices about main() in Python that you just saw: Put code that takes a long time to run or has other effects on the computer in a function or class, so you can control exactly when that code is executed. Has the cause of a rocket failure ever been mis-identified, such that another launch failed due to the same problem? By proactively following this convention ourselves, our module will have the Fortunately, since the partially populated __main__ There are two special symbols: Example 1: Variable length non-keywords argument, Example 2: Variable length keyword arguments. Modules section of the tutorial. Can my creature spell be countered if I cast a split second spell after it? Now you should execute the execution_methods.py script from the command line, as shown below: In this example, you can see that __name__ has the value '__main__', where the quote symbols (') tell you that the value has the string type. You can read more about defining strings in Basic Data Types in Python. By using our site, you This is especially handy in one particular situation - As mentioned previously, when a module is imported for the first time, the main block in that module is run. You will recieve an email from us shortly. Now lets take a look at the second way that the Python interpreter will execute your code: imports. How to write an empty function in Python - pass statement? line with my_name = "Dinsdale" fixes the program and now it exits with running within that same program can import the top-level environments scope The first line of "executable code" "This is my file to test Python's execution methods. In this way, you can control the execution of the code, rather than letting the Python interpreter execute it as soon as it imports the module. What is Python JSON and How to implement it? Example 2: Polymorphic len () function Then, you changed the conditional block so that it executes main(). same behavior when run directly (i.e. The third print() will first print the phrase The value of __name__ is, and then it will print the representation of the __name__ variable using Pythons built-in repr(). acknowledge that you have read and understood our, Data Structure & Algorithm Classes (Live), Data Structures & Algorithms in JavaScript, Data Structure & Algorithm-Self Paced(C++/JAVA), Full Stack Development with React & Node JS(Live), Android App Development with Kotlin(Live), Python Backend Development with Django(Live), DevOps Engineering - Planning to Production, GATE CS Original Papers and Official Keys, ISRO CS Original Papers and Official Keys, ISRO CS Syllabus for Scientist/Engineer Exam, Python Language advantages and applications, Download and Install Python 3 Latest Version, Statement, Indentation and Comment in Python, How to assign values to variables in Python and other languages, Taking multiple inputs from user in Python, Difference between == and is operator in Python, Python | Set 3 (Strings, Lists, Tuples, Iterations). Whether to apply this practice to your code is a judgment call on your part. Thats an It essentially serves as a starting point for the execution of a program. No spam ever. The last two lines of the script are the conditional block that checks __name__ and runs main() if the if statement is True. How is main executed and why do I need this strange if to execute main. You can read more about modules in Python Modules and Packages An Introduction. Absolute difference betwe python - Why use def main()? - Stack Overflow Easy Normal Medium Hard Master. Its top-level because it imports all other modules that the program needs. Python MySQL Environment Setup Database Connection Creating New Database Creating Tables Insert Operation Read Operation Update Operation Join Operation Performing Transactions Python MongoDB Python MongoDB Python SQLite Python SQLite Python Questions The main (no pun intended) benefit of this (IMHO) is that you can unit test it. You will learn about four best practices to make sure that your code can serve a dual purpose: Remember that the Python interpreter executes all the code in a module when it imports the module. How you utilize this mechanism See venv for an example of a package with a minimal __main__.py __name__ is one such special variable. // The main function to convert infix expression //to postfix printer function infixToPostfix(s) . You can actually give the entry point function in a Python script any name you want! This is because when the Python interpreter encounters the def or class keywords, it only stores those definitions for later use and doesnt actually execute them until you tell it to.