"DEBUG >>> About to print the Zen of Python", "DEBUG >>> Done printing the Zen of Python", DEBUG >>> About to print the Zen of Python, DEBUG >>> Done printing the Zen of Python, Although that way may not be obvious at first unless you're Dutch, "[--help] | [-s
] [first [incr]] last", # If passed to the command line, need to convert, # the optional 3rd argument from string to int, Value: Guido, Expected type for firstname, got , Value: Van Rossum, Expected type for lastname, got , Value: 25, Expected type for age, got , Value: 0, Expected type for age, got , Value: Van, Expected type for lastname, got , Value: Rossum, Expected type for age, got , File "sha1sum_stdin.py", line 32, in , File "sha1sum_stdin.py", line 29, in main, File "sha1sum_stdin.py", line 9, in process_file, return pathlib.Path(filename).read_bytes(), File "/usr/lib/python3.8/pathlib.py", line 1222, in read_bytes, File "/usr/lib/python3.8/pathlib.py", line 1215, in open. Observe that the name of the executable ./main is the sole argument. In the image below, we have declared a variable, and it prints the results: We can also declare the same variable using the main() function, as seen in the image below, giving us the same result. How can I pass arguments to a batch file? Some pip subcommands include list, install, freeze, or uninstall. No spam ever. 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(). Python command line arguments are loose strings. python3 Free Bonus: 5 Thoughts On Python Mastery, a free course for Python developers that shows you the roadmap and the mindset youll need to take your Python skills to the next level. Modify your best_practices.py file so that it looks like the code below: In this example code, the first 10 lines of the file have the same content that they had before. You can use the if __name__ == "__main__" idiom to determine the execution context and conditionally run process_data() only when __name__ is equal to "__main__". The OG. The code below implements a limited version of seq with a regular expression to handle the command line parsing and validation: You can execute the code above by running this command: Try this command with other combinations, including the --help option. You can see that the system has two running instances of the Notepad process. This function is usually called main() and must have a specific return type and arguments according to the language standard. 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. One such a character is the asterisk or star (*): The shell converts main. Theyre not necessarily part of the Unix landscape as they span several operating systems, and theyre deployed with a full ecosystem that requires several commands. The dictionary includes the names of each group as keys and their respective values. You may override this method in a subclass. There are other Python options available at the command line. The answer to this is version- and situation-dependent. It can be characterized by the following elements: Not every command line interface may provide all these elements, but this list isnt exhaustive, either. Why does my stock Samsung Galaxy phone/tablet lack some features compared to other Samsung Galaxy models? The message of the exception is list index out of range. We take your privacy seriously. The parser is a loop that fetches each argument one after another and applies a custom logic based on the semantics of your program. From the sys.argv documentation, you learn that in order to get the original bytes of the Python command line arguments, you can use os.fsencode(). The usual arguments list minus the script name. On the other hand, the Python interpreter executes scripts starting at the top of the file, and there is no specific 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. If I import it as a module would I call the main() function when importing it? In situations like this, however, the main() function is mainly a naming convention, such that we can switch the main with another name, and the function will execute just fine. Guido mentions the definitions of literals, identifiers, operators, and statements like break, continue, or return. You can feed data to the program by typing characters on the keyboard. NOTICE: sys module is named System and written in C that NOT A SOURCE Revisit parse from seq_parse.py to use getopt: getopt.getopt() takes the following arguments: Note that a short option followed by a colon (:) expects an option argument, and that a long option trailed with an equals sign (=) expects an option argument. Python Programming Foundation -Self Paced Course, Data Structures & Algorithms- Self Paced Course, Python | Set 6 (Command Line and Variable Arguments). Now that you can see the differences in how Python handles its different execution modes, its useful for you to know some best practices to use. Python PEP Index PEP 3102; Toggle light / dark / auto colour theme PEP 3102 Keyword-Only Arguments Author: Talin Status: Final Type: Standards Track Created: 22-Apr-2006 Python-Version: 3.0 Post-History: 28-Apr-2006, 19-May-2006 Once the Python interpreter imports the file, you can use any variables, classes, or functions defined in the module youve imported. Python programmers have come up with several conventions to define this starting point. Now youre going to explore a few approaches to apprehend options, option-arguments, and operands. We make use of First and third party cookies to improve our user experience. At the end of this tutorial, we should have learned whether or not it is good practice to have arguments inside main(). If youre interested in researching solutions that rely exclusively on the graphical user interface, then you may consider checking out the following resources: In this tutorial, youve navigated many different aspects of Python command line arguments. Nevertheless, having a defined starting point for the execution of a program is useful for understanding how a program works. Commenting Tips: The most useful comments are those written with the goal of learning from or helping out other students. Leave a comment below and let us know. The content of the shell variable, IFS, can be displayed by running the following command: From the result above, ' \t\n', you identify three delimiters: Prefixing a space with a backslash (\) bypasses the default behavior of the space as a delimiter in the string "Real Python". long_options This is optional parameter and if specified, must be a list of strings with the names of the long options, which should be supported. In most cases, a custom launcher should simply be able to call Py_Main with a hard-coded command line. Overview; ResizeMethod; adjust_brightness; adjust_contrast; adjust_gamma; adjust_hue When you are developing a module or script, you will most likely want to take advantage of modules that someone else has already built, which you can do with the import keyword. Many programming languages have a special function that is automatically executed when an operating system starts to run a program. This means that signals cant be used as a means of inter-thread communication. You can combine -l and -s into -ls, which changes the information displayed in the terminal: An option can take an argument, which is called an option-argument. The team members who worked on this tutorial are: Master Real-World Python Skills With Unlimited Access to RealPython. So fundamental they just call it "C." These articles will walk you through the basics of one of the most foundational computer languages in the world. And the notation If arg_line is -s T 10, then the dictionary becomes {'SEP': 'T', 'OP1': '10'}. For a more gentle introduction to Python command-line parsing, have a look at the argparse tutorial. Lets spice up this example by passing a few Python command line arguments to the same program: The output shows that the number of arguments is 5, and the list of arguments includes the name of the program, main, followed by each word of the phrase "Python Command Line Arguments", which you passed at the command line. The command can take more than one file as arguments: Thanks to the wildcards expansion feature of the Unix terminal, its also possible to provide Python command line arguments with wildcard characters. It is a question of why you must have arguments inside the main() function. The following is my updated Python module based on Jonathan's suggestions: This looks correct to me, and yes if you're looking to use this as a module you would import main. NOTICE: argv[0] is file name. Bryan is a core developer of Cantera, the open-source platform for thermodynamics, chemical kinetics, and transport. The thread executes the function function with the argument list args (which must be a tuple). 2. Next, you are going to learn about how to write your code to make it easy for other Python programmers to follow what you mean. So, we can see here that the first instance is easier to grasp and a better way to write the code because it is briefer. Click offers many niceties that will help you craft a very professional command line interface: There are many other features as well. This is better than putting the code directly into the conditional block because a user can reuse main() if they import your module. As mentioned I'm trying to be able to use the following as a script when used directly or imported as a module into my other code and run from there. Secure your applications and networks with the industry's only network vulnerability scanner to combine SAST, DAST and mobile security. python3 Both main and main2 are arguments, or operands, of the program cp. The program calculates the SHA1 hash of each of the files in the argument list. 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. To allow small programs to be combined, you may have to take into account the three standard streams: The output of a program becomes the input of another one, allowing you to chain small utilities. It is a question of why you must have arguments inside the main () function. -c, --check read SHA1 sums from the FILEs and check them, --tag create a BSD-style checksum, -t, --text read in text mode (default). A: The args list holds the command line args. Below is an example of how to execute tasklist in a command prompt on Windows: Note that the separator for an option is a forward slash (/) instead of a hyphen (-) like the conventions for Unix systems. sqlite3--- SQLite DB-API 2.0 . However, it helps to bridge the gap between an arcane command line interface and a full-fledged graphical user interface. To use Python command line arguments in this tutorial, youll implement some partial features of two utilities from the Unix ecosystem: Youll gain some familiarity with these Unix tools in the following sections. This serves two purposes . sys.argv is globally available to your running Python program. A default argument is an argument that assumes a default value if a value is not Represents a potentially large set of elements. In the function greeting, the argument name is expected to be of type str and the return type str.Subtypes are accepted as arguments. The examples in the following sections show you how to handle the Python command line arguments stored in sys.argv and to overcome typical issues that occur when you try to access them. At this point, you know a few ways to extract options and arguments from the command line. What is the Modify sha1sum.py to handle one or more files as arguments. The validation fails. parse() is applying re.match() to the argument line to extract the proper values and store the data in a dictionary. As a result, the program raises SystemExit with an error message. All modules imported during the execution of the process have direct access to sys.argv. sys.argv is the list of command-line arguments.. len(sys.argv) is the number of command-line arguments. Using Python optional arguments using **kwargs **kwargs is a dictionary of keyword arguments. The module sys holds interfaces to the operating system, and in particular it contains a list with the unfortunate name argv which holds the command line arguments. This manual approach of parsing the Python command line arguments may be sufficient for a simple set of arguments. The second is the list of program arguments left after the option list was stripped. This method getopt.getopt() returns value consisting of two elements: the first is a list of (option, value) pairs. When process_data() executes, it prints some status messages to the output. On Windows, the conventions regarding Python command line arguments are slightly different, in particular, those regarding command line options. Syntax: getopt.getopt(args, options, [long_options])Parameters:args: List of arguments to be passed. 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(). First, youll see an example that introduces a straight approach relying on list comprehensions to collect and separate options from arguments. It then automatically unpacks the arguments from each tuple and passes them to the given function: For example, if you attempt to execute sha1sum_stdin.py with an incorrect file name as an argument, then you get the following: bad_file.txt doesnt exist, but the program attempts to read it. Although never is often better than *right* now. Python Command Line Arguments provides a convenient way to accept some information at the command line while running the program. By using this website, you agree with our Cookies Policy. The input may incorporate any characters, including the carriage return Enter. During the import process, Python executes the statements defined in the specified module (but only the first time you import a module). Site design / logo 2022 Stack Exchange Inc; user contributions licensed under CC BY-SA. rev2022.12.9.43105. The way that you tell the computer to execute code from the command line is slightly different depending on your operating system. Another common practice in Python is to have main() execute other functions, rather than including the task-accomplishing code in main(). When I tried to do it in a jupyter notebook obviously that wasn't going to work. If you are new to Python, you might have noticed that it is possible to run a Python script with or without a main method. Some code is left to be done as an exercise in the file affirm-exercise.py. Help us identify new roles for community members, Proposing a Community-Specific Closure Reason for non-English content, Calling a function of a module by using its name (a string). The first two print some introductory phrases. Argument List: ['test.py', 'arg1', 'arg2', 'arg3'] NOTE As mentioned above, the first argument is always the script name and it is also being counted in Look at the example image below where we have defined the main() function: You will see that in the second image, we switched the main name to alpha, and we can see that the function executes just fine. This chapter documents all the available commands. Python Enhancement Proposals. By using our site, you Take note that m.update() takes a bytes-like object as an argument and that the result of invoking read() after opening a file with the mode rb will return a bytes object. In Python, repr() displays the printable representation of an object. The following example works on Windows and, though it isnt as concise as the original main.py, the same code behaves similarly across platforms: In main_win.py, expand_args relies on glob.glob() to process the shell-style wildcards. I'm currently busy updating my existing modules so that that can be run as script or imported as a module into my other code. When the function returns, the thread silently exits. Another example shows how to invoke Python with -h to display the help: Try this out in your terminal to see the complete help documentation. Unsubscribe any time. To ensure both arguments are stored, youd need to surround the overall string with double quotes ("). Find centralized, trusted content and collaborate around the technologies you use most. The standard library also exposes optparse but its officially deprecated and only mentioned here for your information. You can read more about modules in Python Modules and Packages An Introduction. However, there are slight differences in meaning that emphasize the purpose of a piece of code: File: Typically, a Python file is any file that contains code. If youre using Windows 10, then the most convenient method is to run sha1sum and seq in a Linux environment installed on the WSL. You can read more about repr() in the Python documentation. Python knows the usual control flow statements that other languages speak if, for, while and range with some of its own twists, of course. Following is an example which makes simple use of argparse to accept a name parameter:<>/p>. To log metrics, predictions and model checkpoints to W&B use the command line argument --logger wandb and use the prefix "wandb-" to specify arguments for initializing the wandb run. This method parses command line options and parameter list. An additional if block would also be needed in main(). Although that way may not be obvious at first unless you're Dutch. Overview; ResizeMethod; adjust_brightness; adjust_contrast; adjust_gamma; adjust_hue The arguments that are given after the name of the program in the command line shell of the operating system are known as Command Line Arguments. Introduction to main() function. LockType . unittest.mock provides a core Mock class removing the need to create a host of stubs throughout your test suite. The execution of the code starts from the starting line and goes This could be any of the following: The new seq implementation barely scratches the surface. This is the type of lock objects. In most cases, a custom launcher should simply be able to call Py_Main with a hard-coded command line. More control flow tools in Python 3 "This is my file to test Python's execution methods. There is also a conditional (or if) statement that checks the value of __name__ and compares it to the string "__main__". Notably, they add the long option thats a fully named option prefixed with two hyphens (--). They considered the order of the arguments so that options would not be placed after operands. Negative integers are valid seq arguments. Well start with adding a main() function to the hello.py program above. How do I make function decorators and chain them together? Unsubscribe any time. Python allows mandatory and optional arguments, keyword arguments, and even arbitrary argument lists. What if you want process_data() to execute when you run the script from the command line but not when the Python interpreter imports the file? This is done by parsing Python command line arguments. This is especially useful when you can compose your overall task from several smaller sub-tasks that can execute independently. It handles several commands, each possibly with their own set of options, option-arguments, and arguments. The ** allows us to pass any number of keyword arguments. Module: A Python module is a file that you intend to import from within another module or a script, or from the interactive interpreter. For example, the command cp, which is used to copy one or more files to a file or a directory, takes at least one source and one target: It then copies the content of main to a new file named main2. For something uncomplicated, the following pattern, which doesnt enforce ordering and doesnt handle option-arguments, may be enough: The intent of the program above is to modify the case of the Python command line arguments. Youll delve into argument separators in a later section. The pattern validates the following: For the regular expression to be able to handle these things, it needs to see all Python command line arguments in one string. In the reverse.py example you saw earlier, the first and only argument is "Real Python", and the result is "nohtyP laeR". To address this issue, you want to send traces to the standard errors stream, stderr, instead: Execute zen_sort_stderr.py to observe the following: Now, the traces are displayed to the terminal, but they arent used as input for the sort command. All parameters (arguments) in the Python language are passed by reference. You can actually give the entry point function in a Python script any name you want! To execute that function, we first need to define the function, which is where we will need to define the main() function. The concept of subcommands isnt documented in the POSIX or GNU standards, but it does appear in docopt. _thread. NOTICE: because python written in c , C have main(int argc , char *argv[]); but argc in sys module does not exits. To this effect, youll modify main() and add init_argparse to instantiate argparse.ArgumentParser: For the cost of a few more lines compared to the previous implementation, you get a clean approach to add --help and --version options that didnt exist before. Obtain closed paths using Tikz random decoration on circles. Check out Emulating switch/case Statements in Python if youve never encountered this Python idiom before. The expected arguments (the files to be processed) are all available in field files of object argparse.Namespace. It shows we can declare a simple variable without the need to define main(). You may override this method in a subclass. As Guido Van Rossum wrote in An Introduction to Python for Unix/C Programmers in 1993, C had a strong influence on Python. Execute the script argv.py above with a list of arbitrary arguments as follows: The output confirms that the content of sys.argv[0] is the Python script argv.py, and that the remaining elements of the sys.argv list contains the arguments of the script, ['un', 'deux', 'trois', 'quatre']. See 2to3 Automated Python 2 to 3 code translation. After that, the value of data is printed. Without any arguments, it lists the files and directories in the current directory: Lets add a few options. Then, you changed the conditional block so that it executes main(). 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(). The second is the list of program arguments left after the option list was stripped. So, how could Click help you handle the Python command line arguments? It allows you to replace parts of your system under test with mock objects and make assertions about how they have been used. Note: For more information on how importing works in Python, check out Python import: Advanced Techniques and Tips as well as Absolute vs Relative Imports in Python. You should feel prepared to apply the following skills to your code: Whether youre running a small script or a complex text-based application, when you expose a command line interface youll significantly improve the user experience of your Python software. You can collect them using str.join(): This makes arg_line a string that includes all arguments, except the program name, separated by a space. By default, the runtime expects the method to be implemented as a global method called main() in the __init__.py file. The affirm.py program has a few options to say nice things about a name. NOTICE: argv is not function or class and is variable & can change. When would I give a checkpoint to my D&D party that they can return to if they die? The function main() can be named anything you would like, and that wouldn't affect your program. On Windows, the name of the Python 3 executable is typically python, so you should run Python scripts by typing python script_name.py after the >. In the example above, -t is given type x1, which stands for hexadecimal and one byte per integer. The value of __name__ is: 'execution_methods', "This is my file to demonstrate best practices.". A tool that tries to convert Python 2.x code to Python 3.x code by handling most of the incompatibilities which can be detected by parsing the source and traversing the parse tree. excepthook (type, value, traceback) This function prints out a given traceback and exception to sys.stderr.. Ready to optimize your JavaScript with Rust? 'affirm.py'. You can use this tool in addition to processing Python command line arguments as in the previous examples, but this gives you a path to a UI-like approach without you having to depend on a full Python UI toolkit. best-practices The simpler approach is to provide a batch file or generated shortcut that directly calls the python.exe or pythonw.exe with the required command-line arguments. Youll learn: The sys module exposes an array named argv that includes the following: The following example demonstrates the content of sys.argv: Note: The f-string syntax used in argv.py leverages the new debugging specifier in Python 3.8. This results in one block of text as intended, instead of two. 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__. Note: For more details about the usage of data classes in Python, check out The Ultimate Guide to Data Classes in Python 3.7. You can easily pass command line arguments to a Python script. In this tutorial, we will help you to read the command line arguments in a Python script. Below is the sample Python script, which reads the command line arguments and print details. Create a sample script like script.py and copy below content. Python #!/usr/bin/python import sys You might have noticed that methods like insert, remove or sort that only modify the list have no return value printed they return the default None. Why is this usage of "I've to work" so awkward? To read more about this new f-string feature and others, check out Cool New Features in Python 3.8. As the items of the arguments list unfold, you apply the logic thats expected for your program. 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. Error handling could be addressed in this script the same way you did it in reverse_exc.py. This object is populated on line 17 by calling parse_args(). A push is made to the main branch in the repository; A push is made to a GitHub Pages-enabled branch; on: label: types:-created push: branches:-main page_build: on..types. How are you going to put your newfound skills to use? Keywords and Positional Arguments For calling operators keywords are used for operator properties and positional arguments are used to define how the operator is called. Related Tutorial Categories: Note that the args in the list are always strings. Use the different values of __name__ to determine the context and change the behavior of your code with a conditional statement. However, realize what occurs when you use a single double quote: The command prompt passes the whole string "Real Python" as a single argument, in the same manner as if the argument was "Real Python". Commands Youve already learned how to use the command-line interface to do some things. Not unlike what youve already explored earlier, detailed validation may require some custom approaches. email: Examples. To demonstrate this, we will use the interactive Python interpreter. sleep() pauses the interpreter for however many seconds you give as an argument and will produce a function that takes a long time to run for this example. With the spread of Unix tools making their appearance in the Windows ecosystem, non-Windows-specific conventions are also accepted on Windows. Youre going to revisit sha1sum_val.py, the most recent clone of sha1sum, to introduce the benefits of argparse. Some examples of shell interpreters are Bash on Linux or Command Prompt on Windows. We can also run the above program as follows: This will produce the same result as in case of -i and -o: We can use h option to check the usage of the program: Consider we use some other option which has not been implemented in the program. When we execute the new.py, it also executes the function from main.py. Using Python optional arguments using **kwargs **kwargs is a dictionary of keyword arguments. I've updated the answer to include how to use argparse. The OG. Now that youve explored a few aspects of Python command line arguments, most notably sys.argv, youre going to apply some of the standards that are regularly used by developers while implementing a command line interface. Defining your own functions is an essential skill for writing clean and effective code. It stands for assembler output and is reminiscent of the executables that were generated on older UNIX systems. unittest.mock provides a core Mock class removing the need to create a host of stubs throughout your test suite. should use of sys ( system ) module . For example, let's try to run the same program with wrong option -p as follows: This exception is raised when an unrecognized option is found in the argument list or when an option requiring an argument is given none. You may consider adding the version option as an extended exercise. __name__ takes on different values depending on how you executed your Python file. The reason for asking is that I call two functions within my main() func that use the argument workspace. A push is made to the main branch in the repository; A push is made to a GitHub Pages-enabled branch; on: label: types:-created push: branches:-main page_build: on..types. If you want to reuse functionality from your code, define the logic in functions outside main() and call those functions within main(). A-143, 9th Floor, Sovereign Corporate Tower, We use cookies to ensure you have the best browsing experience on our website. Hi Jonathan, I can't thank you enough, you have been a great help. Here are three runs of the program in the command line. The inputs are currently hard coded to show what I'm trying to achieve. See 2to3 Automated Python 2 to 3 code translation. Many programming languages have a special function that is automatically executed when an operating system starts to run a program. * in the current directory, and passes them to sha1sum. In particular, the command may take: For clarity, the pattern args_pattern above uses the flag re.VERBOSE on line 11. The code checks if the number of args is 2, and the first arg (i.e. You didnt pass an argument at the command line, so theres nothing in the list sys.argv at index 1. You can add as many arguments as you like using add_argument() method, infact you can also provide required data type of the argument as follows. The use of Python command line arguments is also strongly influenced by the C language. sys.argv remains untouched, and args isnt impacted by any inadvertent changes to sys.argv. In other words, it may help to make your tools and programs more user-friendly. Next, you use print() to print a sentence describing the purpose of this code. The file affirm.py has all three command line options working: -affirm, -hello, -n. You can run the program to see what it does, and look at the main() code as an example. In addition, by constructing the data class Arguments with the values of the converted arguments, you obtain two validations: You can see this in action with the following execution: In the execution above, the number of arguments is correct and the type of each argument is also correct. These control sequences send an end of file (EOF) to the terminal, which stops reading from stdin and returns the data that was entered. Represents a potentially large set of elements. However, you can also import the best_practices.py file and re-use process_data() for a different input data source, as shown below: In this example, you imported best_practices and shortened the name to bp for this code. All the programs in this tutorial need to be run from the command line, so we are unable to provide online compile & run option for these programs. fictitious and represent two long options (--verbose and --debug) 1 This is a design principle for all mutable data structures in Python.. Another thing you might notice is that not all data can be sorted or compared. Then, you reused process_data() and write_data_to_database() from the best_practices.py file. See an example in action with od below: od stands for octal dump. The answer to this is version- and situation-dependent. Without any arguments, the program expects the data to be provided in the standard input. script name. We take your privacy seriously. Knowing the value of the __name__ variable is important to write code that serves the dual purpose of executable script and importable module. This means that signals cant be used as a means of inter-thread communication. This function is often called the entry point because it is where execution enters the program. These are the main UNIX standards and references: The standards above define guidelines and nomenclatures for anything related to programs and Python command line arguments. The compilation of main.c assumes that you used a Linux or a Mac OS system. The original. Inside the conditional block, you have added four lines of code (lines 12, 13, 14, and 15): Now, run your best_practices.py script from the command line to see how the output will change: First, the output shows the result of the print() call outside of process_data(). Notice that importing from time and defining process_data() produce no output. In the function greeting, the argument name is expected to be of type str and the return type str.Subtypes are accepted as arguments. By the end of this tutorial, youll know: If you want a user-friendly way to supply Python command line arguments to your program without importing a dedicated library, or if you want to better understand the common basis for the existing libraries that are dedicated to building the Python command line interface, then keep on reading! At a high level, every Spark application consists of a driver program that runs the users main function and executes various parallel operations on a cluster. Check out Writing Python Command-Line Tools With Click to see more concrete examples based on Click. The ** allows us to pass any number of keyword arguments. The two following examples with the Python command illustrates the description of a command line interface: In this first example, the Python interpreter takes option -c for command, which says to execute the Python command line arguments following the option -c as a Python program. $ python test.py arg1 arg2 arg3 The Python sys module provides access to any command-line arguments via the sys.argv.This serves two purposes . 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