Python has a rich and versatile collection of standard libraries, making it one of the better programming languages, so it needs to cover all the areas of programming.<\/p>\n\n\n\n
If developers want to write the scripts for the command line using Python, then there must be some libraries that allow them to write command line scripts conveniently. Python has a library called In this article, we’ll be going to learn:<\/p>\n\n\n\n A command line interface, short for CLI<\/strong>, is a medium or type of interface that allows us to interact with a command line script. Python has many libraries that allow us to write the command line interface for our scripts. We’ll use a library called It is a standard way to create a CLI in Python, and Before we proceed any further, we need to know how the command line interface works, so open up your terminal on your computer and execute a command ‘python’<\/em><\/strong> to start using Python commands in your command line.<\/p>\n\n\n\n Here we can execute the Python commands directly in our CLI. Fortunately, we don’t need any Python interpreter to get started. Still, we can add an option<\/strong>(type of argument) with the argument to get the extra information.<\/p>\n\n\n\n Here we obtained the version of Python that we are currently using by just adding the To understand arguments, options, and parameters, consider the following example:<\/p>\n\n\n\n To explain precisely,<\/p>\n\n\n\n An argument<\/strong> is a command that we want to execute.<\/p>\n\n\n\n An option<\/strong> is part of an argument or type of argument used to modify the behavior of the command line.<\/p>\n\n\n\n A parameter<\/strong> is a type of argument that provides additional information to the command.<\/p>\n\n\n\n We can create an essential command for CLI in a few steps using Let’s assume we have a file named We’ve coded our first-ever command for CLI and now let’s understand our code. We can divide our code into four parts.<\/p>\n\n\n\n First, we imported the Next, we added the argument to the parser<\/strong> using the If we run our command in the CLI without specifying any value, then we will get an error<\/strong> and a usage message<\/strong>.<\/p>\n\n\n\n The program detected that we needed a positional argument<\/strong> ( We can see that our command accepts an optional<\/strong> If we execute our command with the positional<\/strong> argument it needs, we’ll get the desired result.<\/p>\n\n\n\n We learned the basic usage of the The Now we can see the different usage messages<\/strong> if we execute the program.<\/p>\n\n\n\n In the previous section, we saw the Python script name<\/strong> when we executed the program in the CLI because the library uses the We will now see our specified name, We can customize<\/strong> the text we want to display before<\/strong> and after<\/strong> in the help<\/strong> text by using the following keywords.<\/p>\n\n\n\n We have already seen the use of We will see the customized message after the help<\/strong> text.<\/p>\n\n\n\n The optional arguments<\/strong> in the CLI command are generally prefixed with ( The Now, in the output, we won’t see ( Now our program does not support the Python We’ve added the One of the features the Python We can shorten the optional argument until the abbreviation leads to the wrong interpretation.<\/p>\n\n\n\n We can shorten the optional argument until However, we can force users to specify the full name of the option by disabling the feature by adding the Now, if we try to execute the program using an abbreviation, the program will throw an error.<\/p>\n\n\n\n There are two types of arguments that we can use in our command line interface:<\/p>\n\n\n\n Positional arguments<\/strong><\/p>\n\n\n\n In the previous examples, we’ve already seen the positional arguments. In the example above, Positional arguments<\/strong> are the types of argument that we use in command to perform some operation. They are called positional<\/strong> arguments because their position defines their function.<\/p>\n\n\n\n Here, Optional arguments<\/strong><\/p>\n\n\n\n The optional arguments are used to perform the additional tasks, and when they are used, they can modify the command’s behavior at runtime.<\/p>\n\n\n\n For example, if we look at the Optional arguments are not mandatory, and we won’t get any errors if we don’t specify them. They are generally prefixed with a ( Output<\/strong><\/p>\n\n\n\n When we add an argument to the command line interface, we can also define the kind of action to take when the argument is specified.<\/p>\n\n\n\n The argparse<\/code> that helps to create exemplary command-line interfaces for the command-line scripts.<\/p>\n\n\n\n\n
argparse<\/code> in Python<\/strong><\/li>\n\n\n\nargparse<\/code><\/strong><\/li>\n\n\n\nargparse<\/code><\/strong><\/li>\n<\/ul>\n\n\n\n<\/a>What is CLI<\/h1>\n\n\n\n
argparse<\/code> to create a CLI in Python.<\/p>\n\n\n\nargparse<\/code> came as a replacement for the modules like optparse<\/a> and getopt<\/a> because they lacked some significant features.<\/p>\n\n\n\n<\/a>Getting to know CLI<\/h1>\n\n\n\n
>python\n....\nPython 3.10.5 (tags\/v3.10.5:f377153, Jun 6 2022, 16:14:13) [MSC v.1929 64 bit (AMD64)] on win32\nType \"help\", \"copyright\", \"credits\" or \"license\" for more information.\n>>> print(\"Hello Geeks!\")\nHello Geeks!\n>>> 3 % 6\n3\n>>> sum([4, 19, 111])\n134<\/pre><\/div>\n\n\n\n
>python --version\n....\nPython 3.10.5\n\n>python -q\n....\n>>> print(\"Python has started without prompting copyright and version messages.\")\nPython has started without prompting copyright and version messages.<\/pre><\/div>\n\n\n\n
--version<\/code> option to the python<\/code> argument, and in the second command, we used the -q<\/code> option to start the Python interpreter without prompting the version and copyright messages that it usually shows on startup.<\/p>\n\n\n\n>dir \/d \/r D:\\SACHIN\\Pycharm\\cli_flask<\/pre><\/div>\n\n\n\n
\n
<\/a>Creating a basic command using\u00a0argparse<\/h1>\n\n\n\n
argparse<\/code>. Let’s understand the measures included in the process of making the command.<\/p>\n\n\n\n\n
argparse<\/code> because it’s a Python library<\/strong><\/li>\n\n\n\nparse_args()<\/code><\/strong><\/li>\n<\/ul>\n\n\n\ncommand.py<\/code> in which we write the basic command to get the factorial<\/strong> of the integer specified in the command line interface<\/strong> or CLI<\/strong>.<\/p>\n\n\n\n# Importing argparse library\nimport argparse\n\nfrom math import factorial\n\n# Creating the parser\nparser = argparse.ArgumentParser(description='Get the factorial of the integer.')\n\n# Adding the argument\nparser.add_argument('Factorial',\n metavar='integer',\n type=int,\n help='factorial of the integer')\n\n# Executing the parser using parse_args() method\nargs = parser.parse_args()\n\nfact = args.Factorial\nprint(factorial(fact))<\/pre><\/div>\n\n\n\nargparse<\/code> library and then created the parser<\/em><\/strong> using the ArgumentParser()<\/code> method in which we passed the detail<\/code> argument to specify the detail of our command.<\/p>\n\n\n\nadd_argument<\/code> method, which holds the necessary information passed into the arguments inside the method. Finally, we executed our parser<\/strong> using the parse_args()<\/code> method.<\/p>\n\n\n\n>python command.py \nusage: command.py [-h] integer\ncommand.py: error: the following arguments are required: integer<\/pre><\/div>\n\n\n\n
integer<\/code>) to complete the execution, but the execution was interrupted due to the absence of the positional argument.<\/p>\n\n\n\n-h<\/code> flag.<\/p>\n\n\n\n>python command.py -h\nusage: command.py [-h] integer\n\nGet the factorial of the integer.\n\npositional arguments:\n integer factorial of the integer\n\noptions:\n -h, --help show this help message and exit<\/pre><\/div>\n\n\n\n
>python command.py 6 \n720<\/pre><\/div>\n\n\n\n
<\/a>Advanced usage of\u00a0argparse<\/h2>\n\n\n\n
argparse<\/code> library, and now we can create an essential command for CLI. However, this is not it, we can do many more things using this library. We’ll see some advanced usage of the argparse<\/code> library.<\/p>\n\n\n\n<\/a>Display custom help message<\/h3>\n\n\n\n
argparse<\/code> library generates usage help if not provided, but we can customize the help message using the usage<\/code> keyword<\/strong>.<\/p>\n\n\n\nparser = argparse.ArgumentParser(\n usage='command.py [options] integer',\n description='Get the factorial of the integer.')<\/pre><\/div>\n\n\n\n
>python command.py\nusage: factorial [options] integer\nfactorial: error: the following arguments are required: integer<\/pre><\/div>\n\n\n\n
<\/a>Setting the program name<\/h3>\n\n\n\n
sys.argv[0]<\/code> to set the program’s name<\/strong>. However, we can specify the program name using the prog<\/strong><\/code> keyword.<\/p>\n\n\n\nparser = argparse.ArgumentParser(\n prog='factorial',\n description='Get the factorial of the integer.')<\/pre><\/div>\n\n\n\n
factorial<\/code>, of the program in the CLI instead of the Python script name.<\/p>\n\n\n\n>python command.py\nusage: factorial [-h] integer\nfactorial: error: the following arguments are required: integer<\/pre><\/div>\n\n\n\n
<\/a>Displaying text before and after the arguments<\/h3>\n\n\n\n
\n
description<\/strong><\/code>. This time we’ll use the epilog<\/strong><\/code> to display the text after the help<\/strong> text.<\/p>\n\n\n\nparser = argparse.ArgumentParser(\n description='Get the factorial of the integer.',\n epilog='Have you understood the process? ')<\/pre><\/div>\n\n\n\n
>python command.py -h\nusage: command.py [-h] integer\n\nGet the factorial of the integer.\n\npositional arguments:\n integer factorial of the integer\n\noptions:\n -h, --help show this help message and exit\n\nHave you understood the process?<\/pre><\/div>\n\n\n\n
<\/a>Customizing prefix character<\/h3>\n\n\n\n
-<\/code>), a standard prefix char. The argparse<\/code> library has a feature that allows us to customize the prefix chars<\/strong>.<\/p>\n\n\n\nprefix_chars<\/strong><\/code> keyword lets us customize the prefix character while defining the parser.<\/p>\n\n\n\nparser = argparse.ArgumentParser(\n description='Get the factorial of the integer.',\n prefix_chars='$')<\/pre><\/div>\n\n\n\n
-<\/code>) as the prefix char for the optional argument instead, we will see the ($<\/code>) as the prefix char.<\/p>\n\n\n\n>python command.py \nusage: command.py [$h] integer\ncommand.py: error: the following arguments are required: integer<\/pre><\/div>\n\n\n\n
-h<\/code> flag but the $h<\/code> flag. The help text has also changed accordingly.<\/p>\n\n\n\n<\/a>Enable and disable help<\/h3>\n\n\n\n
argparse<\/code> library automatically generates the help text without having to code anything. However, sometimes we wanted to disable the feature. We can add the add_help<\/code> keyword when creating the parser.<\/p>\n\n\n\nparser = argparse.ArgumentParser(\n description='Get the factorial of the integer.',\n add_help=False)<\/pre><\/div>\n\n\n\n
add_help<\/code> keyword in the above code and set its value to False<\/code>. It ensures that the program does not accept the -h<\/code> flag anymore.<\/p>\n\n\n\n>python command.py\nusage: command.py integer\ncommand.py: error: the following arguments are required: integer<\/pre><\/div>\n\n\n\n
<\/a>Allowing and disallowing abbreviation<\/h3>\n\n\n\n
argparse<\/code> library provides is the ability to handle abbreviations. Consider the following example that prints the square of the specified integer.<\/p>\n\n\n\nimport argparse\n\nparser = argparse.ArgumentParser()\nparser.add_argument('--square', action='store', type=int)\nparser.add_argument('--sum', action='store', type=int)\n\nargs = parser.parse_args()\nprint(args.square**2)<\/pre><\/div>\n\n\n\n>python abbreviation.py --square 4 \n16\n\n>python abbreviation.py --squar 4 \n16\n\n>python abbreviation.py --squa 4 \n16\n\n>python abbreviation.py --squ 4 \n16\n\n>python abbreviation.py --sq 4 \n16<\/pre><\/div>\n\n\n\n
--sq 4<\/code>. What happens if we execute the program specifying --s 4<\/code>? It might lead to an error because argparse<\/code> doesn’t know whether we want to specify 4<\/strong> to the --square<\/code> or the --sum<\/code> argument.<\/p>\n\n\n\n>python abbreviation.py --s 4 \nusage: abbreviation.py [-h] [--square SQUARE] [--sum SUM]\nabbreviation.py: error: ambiguous option: --s could match --square, --sum<\/pre><\/div>\n\n\n\n
allow_abbrev<\/code> while creating the parser.<\/p>\n\n\n\nimport argparse\n\nparser = argparse.ArgumentParser(allow_abbrev=False)\nparser.add_argument('--square', action='store', type=int)\nparser.add_argument('--sum', action='store', type=int)\n\nargs = parser.parse_args()\n\nprint(args.square**2)<\/pre><\/div>\n\n\n\n>python abbreviation.py --squa 4 \nusage: abbreviation.py [-h] [--square SQUARE]\nabbreviation.py: error: unrecognized arguments: --squa 4<\/pre><\/div>\n\n\n\n
<\/a>Setting the name or flag of the arguments<\/h3>\n\n\n\n
Factorial<\/code> was the positional argument<\/strong>, and our program couldn’t work without it.<\/p>\n\n\n\nimport argparse\n\nparser = argparse.ArgumentParser()\nparser.add_argument('Square', type=int, help='square of the integer')\n\nargs = parser.parse_args()\n\nprint(args.Square**2)<\/pre><\/div>\n\n\n\nSquare<\/code> is the positional argument, and when we specify an integer, the program returns the square of that integer. By default, the positional argument is treated as a String<\/strong>, so we used the type<\/code> keyword and set its value to int<\/code> to typecast the string into the integer<\/strong>.<\/p>\n\n\n\nls<\/code> command that lists the files in a current directory and if we use the -l<\/code> argument, which is an optional argument, it modifies the output and returns the extra information.<\/p>\n\n\n\n$ ls -l<\/pre><\/div>\n\n\n\n
-<\/code>) dash or (--<\/code>) double dash.<\/p>\n\n\n\nimport argparse\nimport math\n\nparser = argparse.ArgumentParser()\nparser.add_argument('-s', \n '--sq_root', \n type=int, \n help='square root of the integer')\n\nargs = parser.parse_args()\n\nsqrt = args.sq_root\n\nprint(math.sqrt(sqrt))<\/pre><\/div>\n\n\n\n>python op_arg.py --sq_root 9 \n3.0\n\n>python op_arg.py -s 9 \n3.0<\/pre><\/div>\n\n\n\n
<\/a>Setting the action<\/h3>\n\n\n\n
action<\/code> keyword argument specifies how the command-line arguments should be handled. Many actions are available and ready to use:<\/p>\n\n\n\n\n