Python Command line arguments

The Python supports the programs that can be run on the command line, complete with command line arguments. It is the input parameter that needs to be passed to the script when executing them. It means to interact with a command-line interface for the scripts. There are different ways we can use command line arguments, few of them are:

1. Python sys module

It is a basic module that comes with Python distribution from the early versions. It is a similar approach as C library using argc/argv to access the arguments. The sys module implements command-line arguments in a simple list structure named sys.argv.

Each list element represents a single argument. The first one -- sys.argv[0] -- is the name of Python script. The other list elements are sys.argv[1] to sys.argv[n]- are the command line arguments 2 to n. As a delimiter between arguments, space is used. Argument values that contain space in it have to be quoted, accordingly.

It stores command-line arguments into a list; we can access it using sys.argv. This is very useful and a simple way to read command-line arguments as String.

Code

Output:

<class ' list '>
The command line arguments are:
script.py
arg1
arg2

2. Python getopt module

The Python getopt module extends the separation of the input string by parameter validation. Based on getopt C function, it allows both short and long options, including a value assignment.

It is very similar to C getopt() function for parsing command line parameters.

It is useful in parsing command line arguments where we want the user to enter some options.

Code

Output:

[('-h', ''), ('-m', 'my_value'), ('--my_file', 'input.txt')]
['arg1', 'arg2']

3. Python argparse module

It offers a command-line interface with standardized output, whereas the former two solutions leave most of the work in your hands. argparse allows verification of fixed and optional arguments with a name checking as either UNIX or GNU style. It is the preferred way to parse command-line arguments. It provides a lot of option such as positional arguments, the default value for arguments, helps message, specifying the data type of argument etc.

It makes it easy to write the user-friendly command-line interfaces. It automatically generates help and usage messages and issues errors when a user gives invalid arguments to the program. It means to communicate between the writer of a program and user which does not require going into the code and making changes to the script. It provides the ability to a user to enter into the command-line arguments.

Code

Output:

python script.py -f myfile.txt -v
File name : myfile.txt
Verbose mode is enabled

The above three are the common basic modules to operate command line arguments in Python. Other simple modules in Python for command line arguments are:

Docopt

Docopt is used to create command line interfaces. It simplifies the process of parsing command-line arguments and generating help messages. To use docopt, you need to install the library first. You can install it using pip:

Code

Output:

$ python script.py --option1 --option2=value argument_value
{
    '--help': False,
    '--option1': True,
    '--option2': 'value',
    '  ': ' argument_value ',
    '--version': False
}

Fire

Python Fire automatically generates a command line interface; you only need one line of code. Unlike the other modules, it works instantly. You don't need to define any arguments; all the methods are linked by default. To install it, type:

Define or use a class:

Code

Output:

$ python script.py hello
Hello
$ python script.py openfile my_file.txt
Open file 'my_file.txt'

Command Line arguments Modules