Extension for FastAPI to make HTMX easier to use.
FastAPI-HTMX is an opinionated extension for FastAPI to speed up development of lightly interactive web applications. FastAPI-HTMX is implemented as a decorator, so it can be used on endpoints selectively. Furthermore it reduces boilerplate for Jinja2 template handling and allows for rapid prototyping by providing convenient helpers.
install via pip:
$ pip install fastapi-htmx
install via poetry:
$ poetry add fastapi-htmx
Basic example using FastAPI with fastapi-htmx
my_app/api.py:
frompathlibimportPathfromfastapiimportFastAPI, Requestfromfastapi.responsesimportHTMLResponsefromfastapi.templatingimportJinja2Templatesfromfastapi_htmximporthtmx, htmx_initapp=FastAPI()
htmx_init(templates=Jinja2Templates(directory=Path("my_app") /"templates"))
@app.get("/", response_class=HTMLResponse)@htmx("index", "index")asyncdefroot_page(request: Request):
return {"greeting": "Hello World"}
@app.get("/customers", response_class=HTMLResponse)@htmx("customers")asyncdefget_customers(request: Request):
return {"customers": ["John Doe", "Jane Doe"]}Note that:
htmx()got parameters, specifying the Jinja2 template to usehtmx_init()is needed for FastAPI-HTMX to find the templates- There is no direct handling of the template needed, it only needs to be specified and the needed variables need to be returned. This way endpoints can be designed in a familiar way to standard REST endpoints in FastAPI.
- This simplifies modularizing the app later (see below) and also providing a REST API if needed. See the "Usage" section for further examples.
get_customersdoes not respond with the whole web page, but only with a part of it. See the HTMX documentation on how HTMX merges partials into the current web page.
request: Requestalthough not used in the endpoint directly, it is currently required for the decorator to work!
The Jinja2 templates to go along with the above code need to be placed like specified in htmx_init in my_app/templates/ in order for the example to work.
The root page my_app/templates/index.jinja2:
<!DOCTYPE html>
<html>
<head>
<title>Hello FastAPI-HTMX</title>
</head>
<body>
<h1>{{ greeting }}</h1>
<buttonhx-get="/customers"hx-swap="innerHTML"hx-target="#customers_list"
>
Load Data
</button>
<divid="customers_list"></div>
<scriptsrc="https://unpkg.com/htmx.org@1.9.6"></script>
</body>
</html>The partial template to load with HTMXmy_app/templates/customers.jinja2:
<ul>
{%forcustomerincustomers%}
<li>{{ customer }}</li>
{%endfor%}
</ul>The decorator htmx provides the following helpers:
partial_template_nameThe partial template to usefull_template_nameThe full page template to use when URL rewriting + history is used*_template_constructorFor DRY code, in case the logic to gather all needed variables is needed multiple times
Seeing these arguments one might ask themselves: Why all these parameters? The answer is an opinionated take on how to design modular endpoints wit partials and url-rewriting support:
The idea behind FastAPI-HTMX is to maintain a modular structure in the app and with the endpoints. Similar to a REST API with a SPA. This way the frontend can be modular as well. This majorly helps with supporting URL rewriting and the history in the frontend:
- A simple endpoint just answers with the partial.
- Without it, if the URL is rewritten and a user navigates back, reloads the page or copies the URL and opens it in another tab or shares the URL, only the partial would be shown in the browser.
To enable SPA like functionality FastAPI-HTMX uses the concept of partials and fullpages as arguments for the decorator and requires to return a dict of the needed variables. Note that returning anything else than a Mapping like a dict in the route, leads FastAPI-HTMX to return that instead of a template.
In order to support this SPA like functionality in an app, see the following example:
my_app/api_with_constructors.py:
frompathlibimportPathfromfastapiimportFastAPI, Requestfromfastapi.responsesimportHTMLResponsefromfastapi.templatingimportJinja2Templatesfromfastapi_htmximporthtmx, htmx_initapp=FastAPI()
htmx_init(templates=Jinja2Templates(directory=Path("my_app") /"templates"))
defconstruct_customers():
return {"customers": ["John Doe", "Jane Doe"]}
defconstruct_root_page():
return {
"greeting": "Hello World",
**construct_customers()
}
@app.get("/", response_class=HTMLResponse)@htmx("index", "index")asyncdefroot_page(request: Request):
returnconstruct_root_page()
@app.get("/customers", response_class=HTMLResponse)@htmx("customers", "index", construct_customers, construct_root_page)asyncdefget_customers(request: Request):
passNote that:
- The
construct_*functions are added, they now return the dataconstruct_root_pagegathers all variables specified needed for the root page, including those for partials- This also means you must avoid naming conflicts across endpoints, so dicts can be merged.
- Costly operations can still be ignored, just use if statements in the template or similar
- The decorators arguments are extended
- The second argument is the fullpage template which is used when the endpoint is called directly (new tab, navigation or reload)
- E.g. since
construct_root_pagegathers all the data for the whole page, the whole page can be returned to the client
- E.g. since
- The other arguments are just to save some boilerplate code handling the
HX-Requestheader- There is no need to use the arguments for the constructor functions, they are just for convenience. If needed the endpoint can be used for the logic as well. Especially if no URL rewriting is needed.
- The second argument is the fullpage template which is used when the endpoint is called directly (new tab, navigation or reload)
For the above code to work the my_app/templates/index.jinja2 needs to be changed as well. The changes are in the button and target div.
Changed root page my_app/templates/index.jinja2:
<!DOCTYPE html>
<html>
<head>
<title>Hello FastAPI-HTMX</title>
</head>
<body>
<h1>{{ greeting }}</h1>
<buttonhx-get="/customers"hx-push-url="true"hx-swap="innerHTML"hx-target="#customers_list"
>
Load Data
</button>
<divid="customers_list">
{%include'customers.jinja2'%}
</div>
<scriptsrc="https://unpkg.com/htmx.org@1.9.6"></script>
</body>
</html>Note that:
hx-push-url="true"was added to the button- The partial is now loaded by default requiring the main endpoint to also provide the needed variables like shown above
The unchanged partial my_app/templates/customers.jinja2:
<ul>
{%forcustomerincustomers%}
<li>{{ customer }}</li>
{%endfor%}
</ul>To add additional partials and endpoints just repeat the same logic:
- Include the partial in the parent Jinja2 template, like the main template. A hierarchy is possible as well.
- Refactor the partials endpoints logic into a function
- Add it's return value to the parents constructor function like done above in
construct_root_page - Add the parents template and constructor function to the partials endpoints
htmxdecorator arguments
- Add it's return value to the parents constructor function like done above in
In case the htmx() arguments for partial and fullpage callables are not flexible enough, an endpoint can be used like usual. For a bit more convenience the HX-Request header is easily accessible via request.hx_request:
my_app/api_with_hx_request.py:
frompathlibimportPathfromfastapiimportFastAPIfromfastapi.responsesimportHTMLResponsefromfastapi.templatingimportJinja2Templatesfromfastapi_htmximportHXRequest, htmx, htmx_initapp=FastAPI()
htmx_init(templates=Jinja2Templates(directory=Path("my_app") /"templates"))
defmy_partial(email_id: int=None):
return {"email_id": email_id}
deffullpage(email_id: int=None):
return {**my_partial(email_id)}
@app.get("/email/{email_id}", response_class=HTMLResponse)@htmx("email_detail", "index")defget_email(request: HXRequest, email_id: int):
ifrequest.hx_request:
returnmy_partial(email_id)
else:
returnfullpage(email_id)my_app/templates/index.jinja2:
<!DOCTYPE html>
<html><head><title>Hello FastAPI-HTMX</title></head>
<body>
<divid="email_detail">
{%include'email_detail.jinja2'%}
</div>
<scriptsrc="https://unpkg.com/htmx.org@1.9.6"></script>
</body>
</html>my_app/templates/email_detail.jinja2:
<p>{{ email_id }}</p>In order to use custom Jinja2 filters like the following, configure them like below.
my_app/templates/customer.jinja2:
<p>{{ customer.created|datetime_format }}</p>Add custom filters for use in Jinja2 templates:
my_app/api_template_filters.py:
frompathlibimportPathfromdatetimeimportdatetimefromfastapi.templatingimportJinja2Templatesfromfastapi_htmximporthtmx_initdefdatetime_format(value: datetime, format="%H:%M %d.%m.%Y"):
returnvalue.strftime(format) ifvalueisnotNoneelse""templates=Jinja2Templates(directory=Path("my_app") /"templates")
templates.env.filters["datetime_format"] =datetime_formathtmx_init(templates=templates)
# ...For bigger apps, multiple template directories might be needed. For example if the app is split into several modules connected with routers. For this case template collections can be used. With htmx_init() multiple template collections can be defined. In each endpoint instead of the templates name (account) the collection gets specified as well, like this: Tpl(SHOP, "account"). This works for partials and full pages.
my_app/api_multiple_template_paths.py:
frompathlibimportPathfromfastapiimportFastAPI, Requestfromfastapi.responsesimportHTMLResponsefromfastapi.templatingimportJinja2Templatesfromfastapi_htmximporthtmx, htmx_init, TemplateSpecasTplSHOP="shop"BACKEND="backend"app=FastAPI()
templates= {
SHOP: Jinja2Templates(directory=Path("my_app") /SHOP/"templates"),
BACKEND: Jinja2Templates(directory=Path("my_app") /BACKEND/"templates")
}
htmx_init(templates=templates)
@app.get("/account", response_class=HTMLResponse)@htmx(Tpl(SHOP, "account"))asyncdefget_account(request: Request):
pass@app.get("/products", response_class=HTMLResponse)@htmx(Tpl(BACKEND, "products"))asyncdefget_products(request: Request):
passmy_app/shop/templates/account.jinja2:
<h1>My Account</h1>my_app/backend/templates/products.jinja2:
<h1>Products</h1>In case SOME endpoints templates got another file extension than the rest, it can be specified in the @htmx() decorator:
my_app/api_template_file_extension.py:
frompathlibimportPathfromfastapiimportFastAPI, Requestfromfastapi.responsesimportHTMLResponsefromfastapi.templatingimportJinja2Templatesfromfastapi_htmximporthtmx, htmx_initapp=FastAPI()
htmx_init(templates=Jinja2Templates(directory=Path("my_app") /"templates"))
@app.get("/customers", response_class=HTMLResponse)@htmx("customers", template_extension="html")asyncdefget_customers(request: Request):
pass# ...my_app/templates/customers.html:
<h1>Customer</h1>In case ALL endpoints templates got another file extension than the default jinja2, it can be overriden in htmx_init() like this:
my_app/api_template_file_extension.py:
frompathlibimportPathfromfastapiimportFastAPI, Requestfromfastapi.responsesimportHTMLResponsefromfastapi.templatingimportJinja2Templatesfromfastapi_htmximporthtmx, htmx_initapp=FastAPI()
templates=Jinja2Templates(directory=Path("my_app") /"templates")
htmx_init(templates=templates, file_extension="html")
@app.get("/customers", response_class=HTMLResponse)@htmx("customers")asyncdefget_customers(request: Request):
passmy_app/templates/customers.html:
<h1>Customer</h1>