# Exceptions and Errors

When your code has errors and you run it, it will show the error and an exception.

Typer does some tricks to help you detect those errors quickly.

## Example Broken App

Let's take this example broken app:

{ docs_src/exceptions/tutorial001.py hl[5] }

This code is broken because you can't sum a string and a number (`name + 3`).

## Exceptions with Rich

If you have Rich installed (for example if you installed `"typer[all]"`), Typer will use it to automatically show you nicely printed errors.

It will omit all the parts of the traceback (the chain of things that called your function) that come from the internal parts in Typer and Click.

So, the error you see will be much clearer and simpler, to help you detect the problem in your code quickly:

    $ python main.py

    <font color="#F92672">╭──────────────── </font><font color="#F92672"><b>Traceback (most recent call last)</b></font><font color="#F92672"> ────────────────╮</font>
    <font color="#F92672">│</font> <font color="#A37F4E">/home/user/code/superapp/</font><font color="#F4BF75"><b>main.py</b></font>:<font color="#66D9EF">5</font> in <font color="#A6E22E">main</font>                        <font color="#F92672">│</font>
    <font color="#F92672">│</font>                                                                   <font color="#F92672">│</font>
    <font color="#F92672">│</font>    2                                                              <font color="#F92672">│</font>
    <font color="#F92672">│</font>    3                                                              <font color="#F92672">│</font>
    <font color="#F92672">│</font>    4 <font color="#66D9EF">def</font> <font color="#A6E22E">main</font>(name: <font color="#A1EFE4">str</font> = <font color="#F4BF75">&quot;morty&quot;</font>):                               <font color="#F92672">│</font>
    <font color="#F92672">│</font> <font color="#F92672">❱ </font> 5 │   <font color="#A1EFE4">print</font>(name + <font color="#66D9EF">3</font>)                                          <font color="#F92672">│</font>
    <font color="#F92672">│</font>    6                                                              <font color="#F92672">│</font>
    <font color="#F92672">│</font>    7                                                              <font color="#F92672">│</font>
    <font color="#F92672">│</font>    8 <font color="#66D9EF">if</font> <font color="#F92672">__name__</font> == <font color="#F4BF75">&quot;__main__&quot;</font>:                                   <font color="#F92672">│</font>
    <font color="#F92672">│</font>                                                                   <font color="#F92672">│</font>
    <font color="#F92672">│</font> <font color="#F4BF75">╭──── locals ────╮</font>                                                <font color="#F92672">│</font>
    <font color="#F92672">│</font> <font color="#F4BF75">│</font> name = <font color="#F4BF75">&apos;morty&apos;</font> <font color="#F4BF75">│</font>                                                <font color="#F92672">│</font>
    <font color="#F92672">│</font> <font color="#F4BF75">╰────────────────╯</font>                                                <font color="#F92672">│</font>
    <font color="#F92672">╰───────────────────────────────────────────────────────────────────╯</font>
    <font color="#F92672"><b>TypeError: </b></font>can only concatenate str <b>(</b>not <font color="#A6E22E">&quot;int&quot;</font><b>)</b> to str

## Exceptions without Rich

If you don't have Rich installed, Typer will still do some tricks to show you the information as clearly as possible:

    $ python main.py

    Traceback (most recent call last):

      File "main.py", line 12, in <module>
        typer.run(main)

      File "main.py", line 8, in main
        print(name + 3)

    TypeError: can only concatenate str (not "int") to str

## Disable Local Variables for Security

If your Typer application handles delicate information, for example a password, a key, a token, then it could be problematic if the automatic errors show the value in those local variables.

This would be relevant in particular if your CLI application is being run on some CI (continuous integration) system that is recording the logs.

The default errors above, when using Rich, show a section with:

    name = 'morty'

In this case, `name` is a local variable, it comes from a parameter passed to the function.

But if it was something like a password, you would have liked to hide it.

In that case, you can create the `typer.Typer()` application explicitly and set the parameter `pretty_exceptions_show_locals=False`:

{ docs_src/exceptions/tutorial002.py hl[3] }

And now when you run it, you will see the error without the local variables:

    $ python main.py supersecret

    <font color="#F92672">╭──────────────── </font><font color="#F92672"><b>Traceback (most recent call last)</b></font><font color="#F92672"> ────────────────╮</font>
    <font color="#F92672">│</font> <font color="#A37F4E">/home/user/code/superapp/</font><font color="#F4BF75"><b>main.py</b></font>:<font color="#66D9EF">8</font> in <font color="#A6E22E">main</font>                        <font color="#F92672">│</font>
    <font color="#F92672">│</font>                                                                   <font color="#F92672">│</font>
    <font color="#F92672">│</font>    5                                                              <font color="#F92672">│</font>
    <font color="#F92672">│</font>    6 <font color="#AE81FF"><b>@app</b></font>.command()                                               <font color="#F92672">│</font>
    <font color="#F92672">│</font>    7 <font color="#66D9EF">def</font> <font color="#A6E22E">main</font>(password: <font color="#A1EFE4">str</font>):                                     <font color="#F92672">│</font>
    <font color="#F92672">│</font> <font color="#F92672">❱ </font> 8 │   <font color="#A1EFE4">print</font>(password + <font color="#66D9EF">3</font>)                                      <font color="#F92672">│</font>
    <font color="#F92672">│</font>    9                                                              <font color="#F92672">│</font>
    <font color="#F92672">│</font>   10                                                              <font color="#F92672">│</font>
    <font color="#F92672">│</font>   11 <font color="#66D9EF">if</font> <font color="#F92672">__name__</font> == <font color="#F4BF75">&quot;__main__&quot;</font>:                                   <font color="#F92672">│</font>
    <font color="#F92672">╰───────────────────────────────────────────────────────────────────╯</font>
    <font color="#F92672"><b>TypeError: </b></font>can only concatenate str <b>(</b>not <font color="#A6E22E">&quot;int&quot;</font><b>)</b> to str

Note that you passed the password `supersecret`, but it's not shown anywhere in the error message.

Being able to see the values of local variables is normally very helpful to diagnose, debug, and fix problems, but if you are dealing with delicate information, now you know how to secure it. 🔒

## Disable Short Output

If you want to show the full exception, including the parts in Typer and Click, you can use the parameter `pretty_exceptions_short=False`:

{ docs_src/exceptions/tutorial003.py hl[3] }

Now when you run it, you will see the whole output:

    $ python main.py

    <font color="#F92672">╭──────────────── </font><font color="#F92672"><b>Traceback (most recent call last)</b></font><font color="#F92672"> ────────────────╮</font>
    <font color="#F92672">│</font> <font color="#A37F4E">/home/user/code/superapp/</font><font color="#F4BF75"><b>main.py</b></font>:<font color="#66D9EF">12</font> in <font color="#A6E22E">&lt;module&gt;</font>                   <font color="#F92672">│</font>
    <font color="#F92672">│</font>                                                                   <font color="#F92672">│</font>
    <font color="#F92672">│</font>    9                                                              <font color="#F92672">│</font>
    <font color="#F92672">│</font>   10                                                              <font color="#F92672">│</font>
    <font color="#F92672">│</font>   11 <font color="#66D9EF">if</font> <font color="#F92672">__name__</font> == <font color="#F4BF75">&quot;__main__&quot;</font>:                                   <font color="#F92672">│</font>
    <font color="#F92672">│</font> <font color="#F92672">❱ </font>12 │   app()                                                    <font color="#F92672">│</font>
    <font color="#F92672">│</font>   13                                                              <font color="#F92672">│</font>
    <font color="#F92672">│</font>                                                                   <font color="#F92672">│</font>
    <font color="#F92672">│</font> <font color="#F4BF75">╭─────────────────────────── locals ────────────────────────────╮</font> <font color="#F92672">│</font>
    <font color="#F92672">│</font> <font color="#F4BF75">│</font> <font color="#A6194C">__annotations__</font> = <b>{}</b>                                          <font color="#F4BF75">│</font> <font color="#F92672">│</font>
    <font color="#F92672">│</font> <font color="#F4BF75">│</font>    <font color="#A6194C">__builtins__</font> = <b>&lt;</b><font color="#AE81FF"><b>module</b></font> <font color="#F4BF75">&apos;builtins&apos;</font> <b>(</b>built-in<b>)&gt;</b>              <font color="#F4BF75">│</font> <font color="#F92672">│</font>
    <font color="#F92672">│</font> <font color="#F4BF75">│</font>      <font color="#A6194C">__cached__</font> = <font color="#66D9EF">None</font>                                        <font color="#F4BF75">│</font> <font color="#F92672">│</font>
    <font color="#F92672">│</font> <font color="#F4BF75">│</font>         <font color="#A6194C">__doc__</font> = <font color="#66D9EF">None</font>                                        <font color="#F4BF75">│</font> <font color="#F92672">│</font>
    <font color="#F92672">│</font> <font color="#F4BF75">│</font>        <font color="#A6194C">__file__</font> = <font color="#F4BF75">&apos;main.py&apos;</font>                                   <font color="#F4BF75">│</font> <font color="#F92672">│</font>
    <font color="#F92672">│</font> <font color="#F4BF75">│</font>      <font color="#A6194C">__loader__</font> = <b>&lt;</b><font color="#AE81FF"><b>_frozen_importlib_external.SourceFileLoad…</b></font> <font color="#F4BF75">│</font> <font color="#F92672">│</font>
    <font color="#F92672">│</font> <font color="#F4BF75">│</font>                   object at <font color="#66D9EF">0x7f047db1c050</font><b>&gt;</b>                   <font color="#F4BF75">│</font> <font color="#F92672">│</font>
    <font color="#F92672">│</font> <font color="#F4BF75">│</font>        <font color="#A6194C">__name__</font> = <font color="#F4BF75">&apos;__main__&apos;</font>                                  <font color="#F4BF75">│</font> <font color="#F92672">│</font>
    <font color="#F92672">│</font> <font color="#F4BF75">│</font>     <font color="#A6194C">__package__</font> = <font color="#66D9EF">None</font>                                        <font color="#F4BF75">│</font> <font color="#F92672">│</font>
    <font color="#F92672">│</font> <font color="#F4BF75">│</font>        <font color="#A6194C">__spec__</font> = <font color="#66D9EF">None</font>                                        <font color="#F4BF75">│</font> <font color="#F92672">│</font>
    <font color="#F92672">│</font> <font color="#F4BF75">│</font>             app = <b>&lt;</b><font color="#AE81FF"><b>typer.main.Typer</b></font> object at <font color="#66D9EF">0x7f047db51d90</font><b>&gt;</b> <font color="#F4BF75">│</font> <font color="#F92672">│</font>
    <font color="#F92672">│</font> <font color="#F4BF75">│</font>            main = <b>&lt;</b><font color="#AE81FF"><b>function</b></font> main at <font color="#66D9EF">0x7f047db56830</font><b>&gt;</b>           <font color="#F4BF75">│</font> <font color="#F92672">│</font>
    <font color="#F92672">│</font> <font color="#F4BF75">│</font>           typer = <b>&lt;</b><font color="#AE81FF"><b>module</b></font> <font color="#F4BF75">&apos;typer&apos;</font> from                        <font color="#F4BF75">│</font> <font color="#F92672">│</font>
    <font color="#F92672">│</font> <font color="#F4BF75">│</font>                   <font color="#F4BF75">&apos;/home/user/code/superapp/env/lib/python3.…</font> <font color="#F4BF75">│</font> <font color="#F92672">│</font>
    <font color="#F92672">│</font> <font color="#F4BF75">╰───────────────────────────────────────────────────────────────╯</font> <font color="#F92672">│</font>
    <font color="#F92672">│</font>                                                                   <font color="#F92672">│</font>
    <font color="#F92672">│</font> <font color="#A37F4E">/home/user/code/superapp/env/lib/python3.7/site-packages/typer/</font><font color="#F4BF75"><b>ma</b></font> <font color="#F92672">│</font>
    <font color="#F92672">│</font> <font color="#F4BF75"><b>in.py</b></font>:<font color="#66D9EF">328</font> in <font color="#A6E22E">__call__</font>                                             <font color="#F92672">│</font>
    <font color="#F92672">│</font>                                                                   <font color="#F92672">│</font>
    <font color="#F92672">│</font> <font color="#A37F4E">/home/user/code/superapp/env/lib/python3.7/site-packages/typer/</font><font color="#F4BF75"><b>ma</b></font> <font color="#F92672">│</font>
    <font color="#F92672">│</font> <font color="#F4BF75"><b>in.py</b></font>:<font color="#66D9EF">311</font> in <font color="#A6E22E">__call__</font>                                             <font color="#F92672">│</font>
    <font color="#F92672">│</font>                                                                   <font color="#F92672">│</font>
    <font color="#F92672">│</font> <font color="#A37F4E">/home/user/code/superapp/env/lib/python3.7/site-packages/click/</font><font color="#F4BF75"><b>co</b></font> <font color="#F92672">│</font>
    <font color="#F92672">│</font> <font color="#F4BF75"><b>re.py</b></font>:<font color="#66D9EF">1130</font> in <font color="#A6E22E">__call__</font>                                            <font color="#F92672">│</font>
    <font color="#F92672">│</font>                                                                   <font color="#F92672">│</font>
    <font color="#F92672">│</font> <font color="#A37F4E">/home/user/code/superapp/env/lib/python3.7/site-packages/typer/</font><font color="#F4BF75"><b>co</b></font> <font color="#F92672">│</font>
    <font color="#F92672">│</font> <font color="#F4BF75"><b>re.py</b></font>:<font color="#66D9EF">723</font> in <font color="#A6E22E">main</font>                                                 <font color="#F92672">│</font>
    <font color="#F92672">│</font>                                                                   <font color="#F92672">│</font>
    <font color="#F92672">│</font> <font color="#A37F4E">/home/user/code/superapp/env/lib/python3.7/site-packages/typer/</font><font color="#F4BF75"><b>co</b></font> <font color="#F92672">│</font>
    <font color="#F92672">│</font> <font color="#F4BF75"><b>re.py</b></font>:<font color="#66D9EF">216</font> in <font color="#A6E22E">_main</font>                                                <font color="#F92672">│</font>
    <font color="#F92672">│</font>                                                                   <font color="#F92672">│</font>
    <font color="#F92672">│</font> <font color="#A37F4E">/home/user/code/superapp/env/lib/python3.7/site-packages/click/</font><font color="#F4BF75"><b>co</b></font> <font color="#F92672">│</font>
    <font color="#F92672">│</font> <font color="#F4BF75"><b>re.py</b></font>:<font color="#66D9EF">1404</font> in <font color="#A6E22E">invoke</font>                                              <font color="#F92672">│</font>
    <font color="#F92672">│</font>                                                                   <font color="#F92672">│</font>
    <font color="#F92672">│</font> <font color="#A37F4E">/home/user/code/superapp/env/lib/python3.7/site-packages/click/</font><font color="#F4BF75"><b>co</b></font> <font color="#F92672">│</font>
    <font color="#F92672">│</font> <font color="#F4BF75"><b>re.py</b></font>:<font color="#66D9EF">760</font> in <font color="#A6E22E">invoke</font>                                               <font color="#F92672">│</font>
    <font color="#F92672">│</font>                                                                   <font color="#F92672">│</font>
    <font color="#F92672">│</font> <font color="#A37F4E">/home/user/code/superapp/env/lib/python3.7/site-packages/typer/</font><font color="#F4BF75"><b>ma</b></font> <font color="#F92672">│</font>
    <font color="#F92672">│</font> <font color="#F4BF75"><b>in.py</b></font>:<font color="#66D9EF">683</font> in <font color="#A6E22E">wrapper</font>                                              <font color="#F92672">│</font>
    <font color="#F92672">│</font>                                                                   <font color="#F92672">│</font>
    <font color="#F92672">│</font> <font color="#A37F4E">/home/user/code/superapp/</font><font color="#F4BF75"><b>main.py</b></font>:<font color="#66D9EF">8</font> in <font color="#A6E22E">main</font>                        <font color="#F92672">│</font>
    <font color="#F92672">│</font>                                                                   <font color="#F92672">│</font>
    <font color="#F92672">│</font>    5                                                              <font color="#F92672">│</font>
    <font color="#F92672">│</font>    6 <font color="#AE81FF"><b>@app</b></font>.command()                                               <font color="#F92672">│</font>
    <font color="#F92672">│</font>    7 <font color="#66D9EF">def</font> <font color="#A6E22E">main</font>(name: <font color="#A1EFE4">str</font> = <font color="#F4BF75">&quot;morty&quot;</font>):                               <font color="#F92672">│</font>
    <font color="#F92672">│</font> <font color="#F92672">❱ </font> 8 │   <font color="#A1EFE4">print</font>(name + <font color="#66D9EF">3</font>)                                          <font color="#F92672">│</font>
    <font color="#F92672">│</font>    9                                                              <font color="#F92672">│</font>
    <font color="#F92672">│</font>   10                                                              <font color="#F92672">│</font>
    <font color="#F92672">│</font>   11 <font color="#66D9EF">if</font> <font color="#F92672">__name__</font> == <font color="#F4BF75">&quot;__main__&quot;</font>:                                   <font color="#F92672">│</font>
    <font color="#F92672">│</font>                                                                   <font color="#F92672">│</font>
    <font color="#F92672">│</font> <font color="#F4BF75">╭──── locals ────╮</font>                                                <font color="#F92672">│</font>
    <font color="#F92672">│</font> <font color="#F4BF75">│</font> name = <font color="#F4BF75">&apos;morty&apos;</font> <font color="#F4BF75">│</font>                                                <font color="#F92672">│</font>
    <font color="#F92672">│</font> <font color="#F4BF75">╰────────────────╯</font>                                                <font color="#F92672">│</font>
    <font color="#F92672">╰───────────────────────────────────────────────────────────────────╯</font>
    <font color="#F92672"><b>TypeError: </b></font>can only concatenate str <b>(</b>not <font color="#A6E22E">&quot;int&quot;</font><b>)</b> to str

## Disable Pretty Exceptions

You can also entirely disable pretty exceptions with the parameter `pretty_exceptions_enable=False`:

{ docs_src/exceptions/tutorial004.py hl[3] }

And now you will see the full standard exception as with any other Python program:

    $ python main.py

    Traceback (most recent call last):
      File "main.py", line 12, in <module>
        app()
      File "/home/user/code/superapp/env/lib/python3.7/site-packages/typer/main.py", line 328, in __call__
        raise e
      File "/home/user/code/superapp/env/lib/python3.7/site-packages/typer/main.py", line 311, in __call__
        return get_command(self)(*args, **kwargs)
      File "/home/user/code/superapp/env/lib/python3.7/site-packages/click/core.py", line 1130, in __call__
        return self.main(*args, **kwargs)
      File "/home/user/code/superapp/env/lib/python3.7/site-packages/typer/core.py", line 723, in main
        **extra,
      File "/home/user/code/superapp/env/lib/python3.7/site-packages/typer/core.py", line 216, in _main
        rv = self.invoke(ctx)
      File "/home/user/code/superapp/env/lib/python3.7/site-packages/click/core.py", line 1404, in invoke
        return ctx.invoke(self.callback, **ctx.params)
      File "/home/user/code/superapp/env/lib/python3.7/site-packages/click/core.py", line 760, in invoke
        return __callback(*args, **kwargs)
      File "/home/user/code/superapp/env/lib/python3.7/site-packages/typer/main.py", line 683, in wrapper
        return callback(**use_params)  # type: ignore
      File "main.py", line 8, in main
        print(name + 3)
    TypeError: can only concatenate str (not "int") to str

You could also achieve the same with the environment variable `_TYPER_STANDARD_TRACEBACK=1`.

This will work for any other Typer program too, in case you need to debug a problem in a Typer program made by someone else:

    export _TYPER_STANDARD_TRACEBACK=1
    $ python main.py

    Traceback (most recent call last):
      File "main.py", line 12, in <module>
        app()
      File "/home/user/code/superapp/env/lib/python3.7/site-packages/typer/main.py", line 328, in __call__
        raise e
      File "/home/user/code/superapp/env/lib/python3.7/site-packages/typer/main.py", line 311, in __call__
        return get_command(self)(*args, **kwargs)
      File "/home/user/code/superapp/env/lib/python3.7/site-packages/click/core.py", line 1130, in __call__
        return self.main(*args, **kwargs)
      File "/home/user/code/superapp/env/lib/python3.7/site-packages/typer/core.py", line 723, in main
        **extra,
      File "/home/user/code/superapp/env/lib/python3.7/site-packages/typer/core.py", line 216, in _main
        rv = self.invoke(ctx)
      File "/home/user/code/superapp/env/lib/python3.7/site-packages/click/core.py", line 1404, in invoke
        return ctx.invoke(self.callback, **ctx.params)
      File "/home/user/code/superapp/env/lib/python3.7/site-packages/click/core.py", line 760, in invoke
        return __callback(*args, **kwargs)
      File "/home/user/code/superapp/env/lib/python3.7/site-packages/typer/main.py", line 683, in wrapper
        return callback(**use_params)  # type: ignore
      File "main.py", line 8, in main
        print(name + 3)
    TypeError: can only concatenate str (not "int") to str

tiangolo/typer « Previous Next »