You can use typer.echo()
to print to the screen:
{!../docs_src/first_steps/tutorial001.py!}
The reason to use typer.echo()
instead of just print()
is that it applies some error corrections in case the terminal is misconfigured, and it will properly output color if it's supported.
!!! info
typer.echo()
comes directly from Click, you can read more about it in Click's docs.
Check it:
$ python main.py
Hello World
!!! info
For colors to work correctly on Windows you need to also install colorama
.
You don't need to call `colorama.init()`. Typer (actually Click) will handle it underneath.
And make sure you use `typer.echo()` instead of `print()`.
!!! note "Technical Details" The way color works in terminals is by using some codes (ANSI escape sequences) as part of the text.
So, a colored text is still just a `str`.
You can create colored strings to output to the terminal with typer.style()
, that gives you str
s that you can then pass to typer.echo()
:
{!../docs_src/printing/tutorial001.py!}
!!! tip
The parameters fg
and bg
receive strings with the color names for the "foreground" and "background" colors. You could simply pass fg="green"
and bg="red"
.
But **Typer** provides them all as variables like `typer.colors.GREEN` just so you can use autocompletion while selecting them.
Check it:
You can pass these function arguments to typer.style()
:
fg
: the foreground color.bg
: the background color.bold
: enable or disable bold mode.dim
: enable or disable dim mode. This is badly supported.underline
: enable or disable underline.blink
: enable or disable blinking.reverse
: enable or disable inverse rendering (foreground becomes background and the other way round).reset
: by default a reset-all code is added at the end of the string which means that styles do not carry over. This can be disabled to compose styles.
!!! info
You can read more about it in Click's docs about style()
There's a shorter form to style and print at the same time with typer.secho()
it's like typer.echo()
but also adds style like typer.style()
:
{!../docs_src/printing/tutorial002.py!}
Check it:
The way printing works underneath is that the operating system (Linux, Windows, macOS) treats what we print as if our CLI program was writing text to a "virtual file" called "standard output".
When our code "prints" things it is actually "writing" to this "virtual file" of "standard output".
This might seem strange, but that's how the CLI program and the operating system interact with each other.
And then the operating system shows on the screen whatever our CLI program "wrote" to that "virtual file" called "standard output".
And there's another "virtual file" called "standard error" that is normally only used for errors.
But we can also "print" to "standard error". And both are shown on the terminal to the users.
!!! info If you use PowerShell it's quite possible that what you print to "standard error" won't be shown in the terminal.
In PowerShell, to see "standard error" you would have to check the variable `$Error`.
But it will work normally in Bash, Zsh, and Fish.
You can print to "standard error" with typer.echo("some text", err=True)
.
Using err=True
tells Typer (actually Click) that the output should be shown in "standard error".
{!../docs_src/printing/tutorial003.py!}
When you try it in the terminal, it will probably just look the same:
$ python main.py
Here is something written to standard error
As a final detail, when you type text in your keyboard to your terminal, the operating system also considers it another "virtual file" that you are writing text to.
This virtual file is called "standard input".
Right now this probably seems quite useless 🤷♂.
But understanding that will come handy in the future, for example for autocompletion and testing.