In short, __name__ variable helps you to check if the file is being run directly or if it has been imported. What are Important Advantages and Disadvantages Of Python? A function that is defined inside another function is known as the inner function or nested function. Unsubscribe any time. Example: Python Function Return Statement. It can run with many data types in Python. What are Sets in Python and How to use them? '__main__'. File1. So, lets learn about the execution modes in Python. The way that you tell the computer to execute code from the command line is slightly different depending on your operating system. Then, you reused process_data() and write_data_to_database() from the best_practices.py file. Those other modules can then be Join us and get access to thousands of tutorials, hands-on video courses, and a community of expertPythonistas: Master Real-World Python SkillsWith Unlimited Access to RealPython. Creating a function in Python We can create a Python function using the def keyword. Word order in a sentence with two clauses, Short story about swapping bodies as a job; the person who hires the main character misuses his body, What was the purpose of laying hands on the seven in Acts 6:6, Allow a module to provide functionality for import into other code while also providing useful semantics as a standalone script (a command line wrapper around the functionality). Python interpreter, however, runs each line serially from the top of the file and has no explicit main () function. functions to execute from other modules. Python exec () Function Example x = 8 exec('print (x==8)') exec('print (x+4)') Output: True 12 Python sum () Function The details of how you can execute Python from your command line are not that important for the purpose of this article, but you can expand the box below to read more about the differences between the command line on Windows, Linux, and macOS. Mathematical Functions in Python | Set 1 (Numeric Functions), Mathematical Functions in Python | Set 2 (Logarithmic and Power Functions), Mathematical Functions in Python | Set 3 (Trigonometric and Angular Functions), Mathematical Functions in Python | Set 4 (Special Functions and Constants), Time Functions in Python | Set-2 (Date Manipulations), Time Functions in Python | Set 1 (time(), ctime(), sleep()), Calendar Functions in Python | Set 1( calendar(), month(), isleap()), Calendar Functions in Python | Set 2(monthrange(), prcal(), weekday()), Natural Language Processing (NLP) Tutorial, Introduction to Heap - Data Structure and Algorithm Tutorials, Introduction to Segment Trees - Data Structure and Algorithm Tutorials. Given an array A of size N of integers. This function is usually called main() and must have a specific return type and arguments according to the language standard. Lets understand how this code executes. Python Programming Tutorial | Partial Functions in Python | GeeksforGeeks GeeksforGeeks 614K subscribers Subscribe 6.6K views 5 years ago Python Programming Tutorials Find Complete Code. Practice | GeeksforGeeks | A computer science portal for geeks Python Main Function and Examples with Code - Great Learning There is also a conditional (or if) statement that checks the value of __name__ and compares it to the string "__main__". main functions are often used to create command-line tools by specifying Creating a GUI using Tkinter is an easy task. So, if you are running the script directly, Python is going to assign __main__ to __name__, i.e., __name__= __main__. defined in the REPL becomes part of the __main__ scope: Note that in this case the __main__ scope doesnt contain a __file__ For example, you may have a script that does the following: If you implement each of these sub-tasks in separate functions, then it is easy for a you (or another user) to re-use a few of the steps and ignore the ones you dont want. Code within this block wont run unless the module is executed in the 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. How to Call a Function in Python Guide | Python Central There are mainly two types of functions in Python. Complete . 565), Improving the copy in the close modal and post notices - 2023 edition, New blog post from our CEO Prashanth: Community is the future of AI. On the other hand, the Python interpreter executes scripts starting at the top of the file, and there is no specific function that Python automatically executes. This is expanded upon a little more at python.berkely.edu, Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. Top 50 Django Interview Questions and Answers You Need to Know in 2023. Why? 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? top-level environment. That is possible in Python as well (specifically for Python 3.5 and above). if __name__ == '__main__' blocks. easily unit-tested and are properly reusable. Python3 def fun (): How To Implement Round Function In Python? for a __main__.py file within a package, because its __name__ You will find identical output if you include a shebang line in your script and execute it directly (./execution_methods.py), or use the %run magic in IPython or Jupyter Notebooks. Example 1: Input: N = 5 . You will recieve an email from us shortly. 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. Python dictionary is a built-in type that supports key-value pairs. There is noting special about the name. For example: This command will cause __main__.py to run. But once we have a default argument, all the arguments to its right must also have default values. though. A variable created in the main body of the Python code is a global variable and belongs to the global scope. __name__ will be equal to: Now youre ready to go write some awesome Python main() function code! When to use yield instead of return in Python? Thus, it can be said that if __name__ == __main__ is the part of the program that runs when the script is run from the command line using a command like Python File1.py. In this case, __name__ will include the string "__main__". If used, an if __name__ == '__main__' block will still work as expected # for demonstration purposes, you can imagine that there is some, # valuable and reusable logic inside this function, """Echo the input arguments to standard output""", # next section explains the use of sys.exit. Apply function to every row in a Pandas DataFrame - GeeksforGeeks Note: The following examples are defined using syntax 1, try to convert them in syntax 2 for practice. Having a main () function allows you to call its functionality if you import the module. The first string after the function is called the Document string or Docstring in short. Python does not use or require a main() function. Ive also defined a function called demo, to include a piece of code, that can be reused as and when necessary. Nested functions are able to access variables of the enclosing scope. The idea is to put some commonly or repeatedly done tasks together and make a function so that instead of writing the same code again and again for different inputs, we can do the function calls to reuse code contained in it over and over again. The syntax for the return statement is: The return statement can consist of a variable, an expression, or a constant which is returned at the end of the function execution. Now, the main function is like any other function in Python. The code block below shows the result of running this file as a script: The output that we can see here is the result of the first print(). On line 21, main() is defined. If your .py file is primarily intended to be used as a module in other code then you might def test_module() and calling test_module() in your if __name__ == '__main__:' suite. For example, print () function prints the given object to the standard output device (screen) or to the text stream file. Instead, those files are kept short, Python program with main() method does not run, The last else clause in python does not work. What is Python JSON and How to implement it? Regardless of your operating system, the output from the Python scripts that you use in this article will be the same, so only the Linux and macOS style of input is shown in this article, and the input line will start at the $. First, the data is created from read_data_from_web(). How to Set a Single Main Title for All the Subplots in Matplotlib? You can read more about these attributes in the Python Data Model documentation and, specifically for modules and packages, in the Python Import documentation. being isolated and importable elsewhere. How to Display Fibonacci Series in Python? import systems reference for details on how this works. What is the top-level code environment. Important Python Data Types You Need to Know, PyCharm Tutorial: Writing Python Code In PyCharm (IDE), Python Visual Studio- Learn How To Make Your First Python Program. Splitting the work into several functions makes reuse easier but increases the difficulty for someone else trying to interpret your code because they have to follow several jumps in the flow of the program. Is it easy to learn? In the above example, we have declared x and y two variables inside the main function. When process_data() executes, it prints some status messages to the output. You should name your entry point function main() in order to communicate the intention of the function, even though Python does not assign any special significance to a function named main(). This happened because the variable __name__ has the value "__main__" when the Python interpreter executes the file as a script, so the conditional statement evaluated to True. Built-in library function: These are Standard functions in Python that are available to use. Python vs C: Know what are the differences, Python vs C++: Know what are the differences. its __name__ is set to the string '__main__'. And this function is called from within the main() itself. This example uses repr() to emphasize that the value of __name__ is a string. a __main__.py file but rather whichever module that received the special Data Structures & Algorithms in Python - Self Pitched. Now, what will happen when you execute this file as a script on the command line? This is almost always used to separate the portion of code which should be executed from the portions of code which define functionality. Did the Golden Gate Bridge 'flatten' under the weight of 300,000 people in 1987? This is because the __name__ variable had the value "best_practices", so Python did not execute the code inside the block, including process_data(), because the conditional statement evaluated to False. Learn How To Make Python Pattern Programs With Examples. How To Best Implement Armstrong Number In Python? Python Object Oriented Programming (With Examples) Example A variable created outside of a function is global and can be used by anyone: x = 300 def myfunc (): print(x) myfunc () print(x) Try it Yourself In this case, you took advantage of reusing your code instead of defining all of the logic in main(). name '__main__'. In Python a function is defined using the def keyword: Example Get your own Python Server def my_function (): print("Hello from a function") Calling a Function To call a function, use the function name followed by parenthesis: Example Get your own Python Server def my_function (): print("Hello from a function") my_function () Try it Yourself In Python, standard library functions are the built-in functions that can be used directly in our program. Now you are able to write Python code that can be run from the command line as a script and imported without unwanted side effects. By using our site, you This is nothing but the main function, or main() as it is usually denoted. During the import process, Python executes the statements defined in the specified module (but only the first time you import a module). I, personally, like these semantics. Hence, having a defined starting point for the execution of your Python program is useful to better understand how your program works. See Special considerations for __main__ in the Python will know that this logic will be inside this function. Using a main function has the added benefit of the echo function itself interpreter startup, and populates it by running top-level code. .py extension: If the file is part of a package, __name__ will also include the parent On Windows, the command prompt typically looks like the example below: The part before the > may look different, depending on your username. The commands that you type will go after the >. In addition, main() should contain any code that you want to run when the Python interpreter executes the file. Almost there! Next, your script called process_data() and passed data in for modification. How to create a virtual ISO file from /dev/sr0. problem. What is Python language? What is the Format Function in Python and How does it work? Add the code below to the bottom of your best_practices.py file: In this code, youve added a conditional statement that checks the value of __name__. Arguments are the values passed inside the parenthesis of the function. You now know how to create Python main() functions. Threading In Python: Learn How To Work With Threads In Python. The most common way is to execute the file as a Python Script. A main function is used so the file can be imported into a REPL without running as a script, this is what the if statement does. This data is passed to process_data(), which returns the modified_data. The variable __name__ tells me which context this file is running in. How to Learn Python 3 from Scratch A Beginners Guide. named main encapsulates the programs primary behavior: Note that if the module didnt encapsulate code inside the main function However, in practice, modules often define many different variables, functions, and classes. No matter which way of running your code youre using, Python defines a special variable called __name__ that contains a string whose value depends on how the code is being used. if __name__ == "__main__" block of the start module. Script: A Python script is a file that you intend to execute from the command line to accomplish a task. To demonstrate the results of importing your execution_methods.py file, start the interactive Python interpreter and then import your execution_methods.py file: In this code output, you can see that the Python interpreter executes the three calls to print(). a command-line interface for a package. You may look at the output below: When you write full-fledged Python programs, there could be numerous functions that could be called and used. Find centralized, trusted content and collaborate around the technologies you use most. And on execution, it prints Hello, World!. 2023 Brain4ce Education Solutions Pvt. Ideally almost every Python module can do something useful if called from the command line. them as entry points for console scripts. Any code that is not protected by that guard will be executed upon execution or importing of the module. Then, the script will exit without doing anything further, because the script does not have any code that executes process_data(). See runpy for more details on the -m flag to the Make a customized data structure which evaluates functions in O(1) Implement Stack or Queue using Deque; . __name__ is one such special variable. 793k+ curious Nerds. What Isinstance In Python And How To Implement It? By using our site, you Practically, there isnt much difference between them.