# Jinja: NeverUndefined
End the lawless era of Jinja.
`NeverUndefined` is more restrictive than `StrictUndefined`. See [this issue](https://github.com/pallets/jinja/issues/1923).
## Usage
1. Install the package:
```bash
pip3 install jinja2_neverundefined
```
2. Create a template file named `template.j2` with the following content:
```jinja
{% macro test(a, b, c) %}
a macro with three parameters but not used
{%endmacro%}
{{test()}}
```
3. Create a Python script named `example.py` with the following content:
```python
from jinja2 import Environment, FileSystemLoader
from jinja2_neverundefined import NeverUndefined
# Create Jinja2 environment with the extension
env = Environment(
loader=FileSystemLoader('.'),
undefined=NeverUndefined
)
# Render the template
template = env.get_template('template.j2')
rendered = template.render()
# Print the rendered output
print(rendered)
```
4. Run the script:
```bash
python3 example.py
```
The script will raise an exception because parameters `a b c` are not provided when calling macro `test` in the template.
Take another example:
```jinja
{% macro mtest(a, b, c) %}
append undefined parameters to list
{% set s = [] %}
{% do s.append(a) %}
{{ s }}
{% endmacro %}
{{ mtest() }}
```
`StrictUndefined` will not throw error. It will produce:
```
append undefined parameters to list
[Undefined]
```
However, `NeverUndefined` will:
```
File "template.j2", line 9, in top-level template code
{{ mtest() }}
└ <Macro 'mtest'>
File "/usr/local/lib/python3.9/dist-packages/jinja2/runtime.py", line 777, in _invoke
rv = self._func(*arguments)
│ └ [missing, missing, missing]
└ <Macro 'mtest'>
File "template.j2", line 2, in template
{% macro mtest(a, b, c) %}
File "/usr/local/lib/python3.9/dist-packages/jinja2_neverundefined/__init__.py", line 14, in __init__
raise Exception(info)
└ "parameter 'a' was not provided"
Exception: parameter 'a' was not provided
```
By using the `NeverUndefined` extension, the Jinja environment will raise an exception when encountering an undefined variable. This helps catch potential issues or missing variable bindings in your templates.
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"description": "# Jinja: NeverUndefined\n\nEnd the lawless era of Jinja.\n\n`NeverUndefined` is more restrictive than `StrictUndefined`. See [this issue](https://github.com/pallets/jinja/issues/1923).\n\n## Usage\n\n1. Install the package:\n\n ```bash\n pip3 install jinja2_neverundefined\n ```\n\n2. Create a template file named `template.j2` with the following content:\n\n ```jinja\n {% macro test(a, b, c) %}\n a macro with three parameters but not used\n {%endmacro%}\n\n {{test()}}\n ```\n\n3. Create a Python script named `example.py` with the following content:\n\n ```python\n from jinja2 import Environment, FileSystemLoader\n from jinja2_neverundefined import NeverUndefined\n\n # Create Jinja2 environment with the extension\n env = Environment(\n loader=FileSystemLoader('.'),\n undefined=NeverUndefined\n )\n\n # Render the template\n template = env.get_template('template.j2')\n rendered = template.render()\n\n # Print the rendered output\n print(rendered)\n ```\n\n4. Run the script:\n\n ```bash\n python3 example.py\n ```\n\nThe script will raise an exception because parameters `a b c` are not provided when calling macro `test` in the template.\n\nTake another example:\n\n```jinja\n{% macro mtest(a, b, c) %}\nappend undefined parameters to list\n{% set s = [] %}\n{% do s.append(a) %}\n{{ s }}\n{% endmacro %}\n{{ mtest() }}\n```\n\n`StrictUndefined` will not throw error. It will produce:\n\n```\nappend undefined parameters to list\n[Undefined]\n```\n\nHowever, `NeverUndefined` will:\n\n```\n File \"template.j2\", line 9, in top-level template code\n {{ mtest() }}\n \u2514 <Macro 'mtest'>\n File \"/usr/local/lib/python3.9/dist-packages/jinja2/runtime.py\", line 777, in _invoke\n rv = self._func(*arguments)\n \u2502 \u2514 [missing, missing, missing]\n \u2514 <Macro 'mtest'>\n File \"template.j2\", line 2, in template\n {% macro mtest(a, b, c) %}\n File \"/usr/local/lib/python3.9/dist-packages/jinja2_neverundefined/__init__.py\", line 14, in __init__\n raise Exception(info)\n \u2514 \"parameter 'a' was not provided\"\nException: parameter 'a' was not provided\n```\n\nBy using the `NeverUndefined` extension, the Jinja environment will raise an exception when encountering an undefined variable. This helps catch potential issues or missing variable bindings in your templates.\n",
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