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|
# 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:
<div class="termy">
```console
$ 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">"morty"</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">"__main__"</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">'morty'</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">"int"</font><b>)</b> to str
```
</div>
## 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**:
<div class="termy">
```console
$ 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
```
</div>
## 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 <abbr title="a variable that lives only inside a function, its value is only visible inside of it">local variables</abbr>.
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:
```Python
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:
<div class="termy">
```console
$ 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">"__main__"</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">"int"</font><b>)</b> to str
```
</div>
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:
<div class="termy">
```console
$ 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"><module></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">"__main__"</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><</b><font color="#AE81FF"><b>module</b></font> <font color="#F4BF75">'builtins'</font> <b>(</b>built-in<b>)></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">'main.py'</font> <font color="#F4BF75">│</font> <font color="#F92672">│</font>
<font color="#F92672">│</font> <font color="#F4BF75">│</font> <font color="#A6194C">__loader__</font> = <b><</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>></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">'__main__'</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><</b><font color="#AE81FF"><b>typer.main.Typer</b></font> object at <font color="#66D9EF">0x7f047db51d90</font><b>></b> <font color="#F4BF75">│</font> <font color="#F92672">│</font>
<font color="#F92672">│</font> <font color="#F4BF75">│</font> main = <b><</b><font color="#AE81FF"><b>function</b></font> main at <font color="#66D9EF">0x7f047db56830</font><b>></b> <font color="#F4BF75">│</font> <font color="#F92672">│</font>
<font color="#F92672">│</font> <font color="#F4BF75">│</font> typer = <b><</b><font color="#AE81FF"><b>module</b></font> <font color="#F4BF75">'typer'</font> from <font color="#F4BF75">│</font> <font color="#F92672">│</font>
<font color="#F92672">│</font> <font color="#F4BF75">│</font> <font color="#F4BF75">'/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">"morty"</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">"__main__"</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">'morty'</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">"int"</font><b>)</b> to str
```
</div>
## 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:
<div class="termy">
```console
$ 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
```
</div>
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:
<div class="termy">
```console
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
```
</div>
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