{"id":244,"date":"2025-01-06T10:00:00","date_gmt":"2025-01-06T16:00:00","guid":{"rendered":"https:\/\/douglasstarnes.dev\/?p=244"},"modified":"2025-01-08T23:29:28","modified_gmt":"2025-01-09T05:29:28","slug":"building-a-countdown-command-line-application-with-python-typer-sqlmodel-and-rich","status":"publish","type":"post","link":"https:\/\/douglasstarnes.dev\/index.php\/2025\/01\/06\/building-a-countdown-command-line-application-with-python-typer-sqlmodel-and-rich\/","title":{"rendered":"Building a Countdown Command Line Application with Python, Typer, SQLModel and Rich"},"content":{"rendered":"\n

Happy New Year! To get the blog going after the holidays, I am going to write a series of posts (with each post being as short as possible – I’m aiming for 5-7 minutes read time) about building a command line application. The application with use Typer, which is a Python package for creating command line applications. It is written by the maintainer of FastAPI so as you might guess, it makes judicious use of modern Python features such as type hints. The data for the application will be stored in a local SQLite database. The Python standard library includes a module for accessing a SQLite database but as the application grows, it will become tedious constructing SQL statements based on the available options. Instead, we will use SQLModel, a proxy\/wrapper around SQLAlchemy as an ORM. SQLModel is also maintained by the same person who created FastAPI and Typer. Long story short, you’re going to see a lot of Python type hints. And finally, command line applications are text-only. But that doesn’t mean they have to be boring. The rich package lets us use color and formatting as well as UI layouts like tables to make the output of the application easier to read.<\/p>\n\n\n\n

To install Typer, go to the command prompt. In Visual Studio Code, you can press Ctrl-`<\/strong> to open the Terminal pane. At the prompt install Typer with pip<\/code>:<\/p>\n\n\n\n

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$<\/span> <\/span>pip<\/span> <\/span>install<\/span> <\/span>typer<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n
In a new Python file, main.py, write a function that displays some text in the terminal:<\/p>\n\n\n\n
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def<\/span> <\/span>say_hello<\/span>():<\/span><\/span>\n  <\/span>print<\/span>(<\/span>"<\/span>Hey there!<\/span>"<\/span>)<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n
To call this function from a Typer app, we first need to create one. Import the typer <\/code>module, and then create a new instance of a Typer <\/code>application:<\/p>\n\n\n\n
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import<\/span> typer<\/span><\/span>\n<\/span>\napp <\/span>=<\/span> typer<\/span>.<\/span>Typer<\/span>()<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n
Now the say_hello <\/code>function need to be decorated with the command <\/code>decorator.<\/p>\n\n\n\n
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@<\/span>app<\/span>.<\/span>command<\/span>()<\/span><\/span>\ndef<\/span> <\/span>say_hello<\/span>():<\/span><\/span>\n  <\/span>print<\/span>(<\/span>"<\/span>Hey there!<\/span>"<\/span>)<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n
A command in a Typer application is passed to the application at the command line. The name of the command is by default, the same as the decorated function, replacing underscores with dashes. In this case, the name of the command would be say-hello<\/code>.<\/p>\n\n\n\n
Add one more function, decorated with the command <\/code>decorator, to display a farewell message:<\/p>\n\n\n\n
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@<\/span>app<\/span>.<\/span>command<\/span>()<\/span><\/span>\ndef<\/span> <\/span>say_goodbye<\/span>():<\/span><\/span>\n  <\/span>print<\/span>(<\/span>"<\/span>So long!<\/span>"<\/span>)<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n
The last step is to define the entry point. Simply call app <\/code>to get things up and running:<\/p>\n\n\n\n
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if<\/span> __name__ <\/span>==<\/span> <\/span>"<\/span>__main__<\/span>"<\/span>:<\/span><\/span>\n  <\/span>app<\/span>()<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n
Now at the command line, invoke the main.py script, and pass it the name of the say-hello<\/code> command:<\/p>\n\n\n\n
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$<\/span> <\/span>python<\/span> <\/span>main.py<\/span> <\/span>say-hello<\/span><\/span>\nHey<\/span> <\/span>there!<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n
As you might guess, the say-goodbye<\/code> command will invoke the say_goodbye function:<\/p>\n\n\n\n
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$<\/span> <\/span>python<\/span> <\/span>main.py<\/span> <\/span>say-hello<\/span><\/span>\nSo<\/span> <\/span>long!<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n
In addition, you get some built-in help. Invoke main.py with the --help<\/code> option:<\/p>\n\n\n\n
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$<\/span> <\/span>python<\/span> <\/span>main.py<\/span> <\/span>--help<\/span><\/span>\n<\/span>\n <\/span>Usage:<\/span> <\/span>main.py<\/span> [OPTIONS] COMMAND <\/span>[<\/span>ARGS<\/span>]<\/span>...                                <\/span><\/span>\n                                                                           <\/span><\/span>\n\u256d\u2500Options\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u256e<\/span><\/span>\n\u2502<\/span> <\/span>--install-completion<\/span>      <\/span>Install<\/span> <\/span>completion<\/span> <\/span>for<\/span> <\/span>the<\/span> <\/span>current<\/span> <\/span>shell.<\/span> <\/span>\u2502<\/span><\/span>\n\u2502<\/span> <\/span>--show-completion<\/span>         <\/span>Show<\/span> <\/span>completion<\/span> <\/span>for<\/span> <\/span>the<\/span> <\/span>current<\/span> <\/span>shell,<\/span> <\/span>to<\/span> <\/span>\u2502<\/span><\/span>\n\u2502<\/span>                           <\/span>copy<\/span> <\/span>it<\/span> <\/span>or<\/span> <\/span>customize<\/span> <\/span>the<\/span> <\/span>installation.<\/span>    <\/span>\u2502<\/span><\/span>\n\u2502<\/span> <\/span>--help<\/span>                    <\/span>Show<\/span> <\/span>this<\/span> <\/span>message<\/span> <\/span>and<\/span> <\/span>exit.<\/span>               <\/span>\u2502<\/span><\/span>\n\u2570\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u256f<\/span><\/span>\n\u256d\u2500Commands\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u256e<\/span><\/span>\n\u2502<\/span> <\/span>say-hello<\/span>                                                           <\/span>\u2502<\/span><\/span>\n\u2502<\/span> <\/span>say-goodbye<\/span>                                                         <\/span>\u2502<\/span><\/span>\n\u2570\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u256f<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n
Typer automatically provides a list of the commands we registered with the application.  It also show us some default options we can invoke but those are beyond the scope of this post.<\/p>\n\n\n\n
Arguments<\/h3>\n\n\n\n
The point so far is that you get a lot for free from Typer’s built in conventions. There are more conventions that can configure arguments and options to the commands. Modify the say_hello <\/code>function to greet a specific person:<\/p>\n\n\n\n
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@<\/span>app<\/span>.<\/span>command<\/span>()<\/span><\/span>\ndef<\/span> <\/span>say_hello<\/span>(<\/span>name<\/span>:<\/span> <\/span>str<\/span>):<\/span><\/span>\n  <\/span>print<\/span>(<\/span>f<\/span>"Hey there <\/span>{<\/span>name<\/span>}<\/span>"<\/span>)<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n
As mentioned earlier, Typer (along with SQLModel) makes use of type hints. The other thing to notice is what you get when attempting to invoke the say-hello<\/code> command:<\/p>\n\n\n\n
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$<\/span> <\/span>python<\/span> <\/span>main.py<\/span> <\/span>say-hello<\/span><\/span>\nUsage:<\/span> <\/span>main.py<\/span> <\/span>say-hello<\/span> [OPTIONS] NAME<\/span><\/span>\nTry<\/span> <\/span>'<\/span>main.py say-hello --help<\/span>'<\/span> <\/span>for<\/span> <\/span>help.<\/span><\/span>\n\u256d\u2500Error\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u256e<\/span><\/span>\n\u2502<\/span> <\/span>Missing<\/span> <\/span>argument<\/span> <\/span>'<\/span>NAME<\/span>'<\/span>.<\/span>                                             <\/span>\u2502<\/span><\/span>\n\u2570\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u256f<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n
Typer assumes that the name parameter to the say_hello <\/code>function will be an argument to the say-hello<\/code> command. It also suggests running the command with the --help<\/code> option for more details.<\/p>\n\n\n\n
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$<\/span> <\/span>python<\/span> <\/span>main.py<\/span> <\/span>say-hello<\/span> <\/span>--help<\/span><\/span>\n                                                                           <\/span><\/span>\n <\/span>Usage:<\/span> <\/span>main.py<\/span> <\/span>say-hello<\/span> [OPTIONS] NAME                                   <\/span><\/span>\n                                                                           <\/span><\/span>\n\u256d\u2500Arguments\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u256e<\/span><\/span>\n\u2502<\/span> <\/span>*<\/span>    <\/span>name<\/span>      <\/span>TEXT<\/span>  [default: <\/span>None]<\/span> [required]                     \u2502<\/span><\/span>\n\u2570\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u256f<\/span><\/span>\n\u256d\u2500Options\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u256e<\/span><\/span>\n\u2502<\/span> <\/span>--help<\/span>          <\/span>Show<\/span> <\/span>this<\/span> <\/span>message<\/span> <\/span>and<\/span> <\/span>exit.<\/span>                         <\/span>\u2502<\/span><\/span>\n\u2570\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u256f<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n
The --help<\/code> option displays the arguments and options for the command. Here we can see that name is a text argument and is it required. There are no options other than --help<\/code> which is built in. We’ll add options in a minute. But let’s go ahead and invoke the say-hello<\/code> command with the argument:<\/p>\n\n\n\n
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$<\/span> <\/span>python<\/span> <\/span>main.py<\/span> <\/span>say-hello<\/span> <\/span>Typer<\/span><\/span>\nHey<\/span> <\/span>there<\/span> <\/span>Typer!<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n
Options<\/h3>\n\n\n\n
Now let’s add an option that adds exclamation points to the greeting. Options are also passed to the function decorated with the command <\/code>decorator.<\/p>\n\n\n\n
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@<\/span>app<\/span>.<\/span>command<\/span>()<\/span><\/span>\ndef<\/span> <\/span>say_hello<\/span>(<\/span>name<\/span>:<\/span> <\/span>str<\/span>,<\/span> <\/span>enthusiasm<\/span>:<\/span> <\/span>int<\/span> <\/span>=<\/span> <\/span>1<\/span>):<\/span><\/span>\n  <\/span>print<\/span>(<\/span>f<\/span>"Hey there <\/span>{<\/span>name<\/span>}{<\/span>'<\/span>!<\/span>'<\/span> <\/span>*<\/span> enthusiasm<\/span>}<\/span>"<\/span>)<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n
In this example, the enthusiasm <\/code>parameter to the say_hello <\/code>function becomes the --enthusiasm<\/code> option to the say-hello<\/code> command. Notice the enthusiasm <\/code>parameter has a default value of 1. Thus, it is optional and there will be only one exclamation point if the option is omitted. Try it out:<\/p>\n\n\n\n
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$<\/span> <\/span>python<\/span> <\/span>main.py<\/span> <\/span>say-hello<\/span> <\/span>Typer<\/span><\/span>\nHey<\/span> <\/span>there<\/span> <\/span>Typer!<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n
Now include the --enthusiasm<\/code> option and give it a value of 10:<\/p>\n\n\n\n
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$<\/span> <\/span>python<\/span> <\/span>main.py<\/span> <\/span>say-hello<\/span> <\/span>Typer<\/span> <\/span>--enthusiasm<\/span> <\/span>10<\/span><\/span>\nHey<\/span> <\/span>there<\/span> <\/span>Typer!!!!!!!!!!<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n
And take another look at the help for the say-hello<\/code> command:<\/p>\n\n\n\n
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$<\/span> <\/span>python<\/span> <\/span>main.py<\/span> <\/span>say-hello<\/span> <\/span>--help<\/span><\/span>\n                                                                           <\/span><\/span>\n <\/span>Usage:<\/span> <\/span>main.py<\/span> <\/span>say-hello<\/span> [OPTIONS] NAME                                   <\/span><\/span>\n                                                                           <\/span><\/span>\n\u256d\u2500Arguments\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u256e<\/span><\/span>\n\u2502<\/span> <\/span>*<\/span>    <\/span>name<\/span>      <\/span>TEXT<\/span>  [default: <\/span>None]<\/span> [required]                     \u2502<\/span><\/span>\n\u2570\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u256f<\/span><\/span>\n\u256d\u2500Options\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u256e<\/span><\/span>\n\u2502<\/span> <\/span>--enthusiasm<\/span>        <\/span>INTEGER<\/span>  [default: <\/span>1<\/span>]<\/span>                           <\/span>\u2502<\/span><\/span>\n\u2502<\/span> <\/span>--help<\/span>                       <\/span>Show<\/span> <\/span>this<\/span> <\/span>message<\/span> <\/span>and<\/span> <\/span>exit.<\/span>            <\/span>\u2502<\/span><\/span>\n\u2570\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u256f<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n
The help for the --enthusiasm<\/code> option shows that it is an integer and that 1 is the default value.<\/p>\n\n\n\n
Styling with Rich<\/h3>\n\n\n\n
There is one problem with the --enthusiasm<\/code> option, negative numbers are not handled correctly. It won’t make the application crash, but the user won’t know that they shouldn’t use negative numbers. Let’s fix that.<\/p>\n\n\n\n
Add a conditional to check if the --enthusiasm<\/code> option value is less than 0 and print an error if so.<\/p>\n\n\n\n
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@<\/span>app<\/span>.<\/span>command<\/span>()<\/span><\/span>\ndef<\/span> <\/span>say_hello<\/span>(<\/span>name<\/span>:<\/span> <\/span>str<\/span>,<\/span> <\/span>enthusiasm<\/span>:<\/span> <\/span>int<\/span> <\/span>=<\/span> <\/span>1<\/span>):<\/span><\/span>\n  <\/span>if<\/span> enthusiasm <\/span><<\/span> <\/span>0<\/span>:<\/span><\/span>\n    <\/span>print<\/span>(<\/span>"<\/span>Enthusiasm cannot be negative!<\/span>"<\/span>)<\/span><\/span>\n  <\/span>else<\/span>:<\/span><\/span>\n    <\/span>print<\/span>(<\/span>f<\/span>"Hey there <\/span>{<\/span>name<\/span>}{<\/span>'<\/span>!<\/span>'<\/span> <\/span>*<\/span> enthusiasm<\/span>}<\/span>"<\/span>)<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n
Try it out to see the results:<\/p>\n\n\n\n
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$<\/span> <\/span>python<\/span> <\/span>main.py<\/span> <\/span>say-hello<\/span> <\/span>Typer<\/span> <\/span>--enthusiasm<\/span> <\/span>-1<\/span><\/span>\nEnthusiasm<\/span> <\/span>cannot<\/span> <\/span>be<\/span> <\/span>negative<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n
Since this is an error, we should make it obvious to the user. With the Rich package, we can format the error to make it stand out. Let’s style the error in bold red text. Install the Rich package with pip<\/code> to get started<\/p>\n\n\n\n
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$<\/span> <\/span>pip<\/span> <\/span>install<\/span> <\/span>rich<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n
Rich has a special Console <\/code>type that understands how to format text in command line applications. You’ll need to import it and create a new instance of the type:<\/p>\n\n\n\n
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from<\/span> rich<\/span>.<\/span>console <\/span>import<\/span> Console<\/span><\/span>\n<\/span>\nconsole <\/span>=<\/span> <\/span>Console<\/span>()<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n
By calling the print <\/code>method on the console<\/code>, you can markup the text with special tags to make it bold and red.<\/p>\n\n\n\n
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console<\/span>.<\/span>print<\/span>(<\/span>"<\/span>[bold red]Enthusiasm cannot be negative[\/bold red]<\/span>"<\/span>)<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n
Enthusiasm cannot be negative<\/strong><\/code><\/p>\n\n\n\n
However, this will break the DRY principle. It’s likely that we will want to format errors other places in the application. Therefore, using the Style <\/code>type, we can configure a style one time and then apply in multiple places for reusability and maintenance of the code.<\/p>\n\n\n\n
Import the Style <\/code>type from the rich.style<\/code> module.<\/p>\n\n\n\n
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from<\/span> rich<\/span>.<\/span>style <\/span>import<\/span> Style<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n
Also, create a dataclass that will group all of the styles for the application in a single place.  Define the error style to be bold red.  <\/p>\n\n\n\n
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from<\/span> dataclasses <\/span>import<\/span> dataclass<\/span><\/span>\n<\/span>\nclass<\/span> <\/span>ApplicationStyles<\/span>:<\/span><\/span>\n  error<\/span>:<\/span> Style <\/span>=<\/span> <\/span>Style<\/span>(<\/span>color<\/span>=<\/span>"<\/span>red<\/span>"<\/span>,<\/span> <\/span>bold<\/span>=True<\/span>)<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n
Create an instance of the ApplicationStyles <\/code>class.<\/p>\n\n\n\n
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app_styles <\/span>=<\/span> <\/span>ApplicationStyles<\/span>()<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n
Remove the markup from the error message and set the style <\/code>keyword argument of the console.print<\/code> method to the error style.<\/p>\n\n\n\n
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console<\/span>.<\/span>print<\/span>(<\/span>"<\/span>Enthusiasm cannot be negative<\/span>"<\/span>,<\/span> <\/span>style<\/span>=<\/span>app_styles<\/span>.<\/span>error<\/span>)<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n
The end user won’t see anything different. But you’ve just made the code easier to read and maintain by not littering markup in the print functions. As we continue to build the app, we’ll add more style to the ApplicationStyles <\/code>dataclass. So if it seems like overfill right now, stay tuned to see how it will make things easier as the complexity of the applications increases in future posts.<\/p>\n\n\n\n
Summary<\/h3>\n\n\n\n
In this post you learned how to create a simple command line application using Typer.  You learned how to create command functions and register them with the application.  You also learned how to use parameters and type hints to the command functions to create arguments and options to the commands.  And you got a taste of using Rich styles to format text in the application. <\/p>\n","protected":false},"excerpt":{"rendered":"
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