How to easily write beautiful command line programs in Python

Python, originally used as a configuration management language at the time of its birth, has become one of the most popular programming languages, especially as the rise of AI applications has become ubiquitous.

The getopt and optparse modules in Python can be used to develop command-line programs, but they have been deprecated. The argparse module was introduced in versions 2.7 and 3.2; here we use the argparser module, which takes only a few dozen lines of code to make Beautiful command line program.

Take a look at an example from the official documentation:

The functions implemented by these lines of code are: If the command line input does not have the --sum option, the max operation is performed on multiple integers entered; otherwise, the sum operation is performed. For example: execute on the command line: python prog.py 1 2 3 4 output is: 4

Execute in the command line: python prog.py 1 2 3 4 --sum output is: 10

In the above code, the main process is divided into three steps:

Create an ArgumentParser object by calling the constructor of argparse.ArgumentParser.

Call the ArgumentParser's add_argument() method to add the command line parameters, including optional parameters and required parameters. The beginning of ---, - indicates optional parameters, and the other indicates the parameters that must be entered.

Call the parser.parse_args() method to parse the incoming sys.argv argument.

Sometimes, we can group the command line into a series of related subcommands according to the function. For example, the Git command line can be divided into the following groups:

In Python, such a subcommand can be easily made using the argparse module.

For example, we need to do a command-line program that manages user information, including adding, deleting, querying, and more.

We can divide it into three sub-commands according to the function: add, delete, show.

The corresponding code can be written like this:

Explain the above code outline: The add_subparsers() method of the ArgumentParser object creates a special action instance. Call the add_parser() method on the instance to create the ArgumentParser corresponding to the subcommand, and then call the add_argument() of the ArgumentParser instance. Method to add parameters to the subcommand. One convenient point is that the processing function corresponding to the subcommand can be set by the set_defaults() method of ArgumentParser. In the above example, the processing functions are set for the three subcommands: add_fn, delete_fn, show_fn.

Executing in the command line program: python cmd.py --help will display the following information:

As you can see from the help information, the command line is organized into three subcommands, add, delete, and show.

Execute in the command line: python cmd.py add --help , you can view the help information of the add subcommand:

For the add subcommand, it has three parameters, namely the user name, contact address, and phone number; the user name is a mandatory parameter, and the other two are optional parameters.

Execute in the command line: python cmd.py add --name 'Eric' --addr 'California,USA' --phone '0076938377'`

Adding a User's processing logic will be done by add_fn(). The program will get a User with the message {name='Eric', addr='California, USA', phone='0076938377'}.

Other delete and show subcommands are similar to this and will not be described again.

Using Python's argparse module, a few dozen lines of code can be used to build a skeleton of a command-line program.

The most important part of the argparse module is the ArgumentParser object, which contains the following methods:

Add_argument()

Add_subparsers()

Parse_args()