# Request Parameters

Here's the reference information for the request parameters.

These are the special functions that you can put in *path operation function* parameters or dependency functions with `Annotated` to get data from the request.

It includes:

* `Query()`
* `Path()`
* `Body()`
* `Cookie()`
* `Header()`
* `Form()`
* `File()`

You can import them all directly from `fastapi`:

```python

</p>

<pre>
math.Atan2(x, y)  // function call
var pt *Point
pt.Scale(3.5)     // method call with receiver pt
</pre>

<p>
In a function call, the function value and arguments are evaluated in
<a href="#Order_of_evaluation">the usual order</a>.
After they are evaluated, the parameters of the call are passed by value to the function
and the called function begins execution.

import static java.util.concurrent.TimeUnit.SECONDS;

import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.GwtIncompatible;
import com.google.common.base.Function;
import com.google.common.base.Functions;
import com.google.common.base.Joiner;
import com.google.common.base.Predicate;
import com.google.common.base.Predicates;
import com.google.common.collect.testing.IteratorFeature;

  // it in this context.
  virtual AbstractOperation* CreateOperation() = 0;

  // Registers a function with this context, after this the function is
  // available to be called/referenced by its name in this context.
  virtual absl::Status RegisterFunction(AbstractFunction*) = 0;
  // Remove a function. 'func' argument is the name of a previously added
  // FunctionDef. The name is in fdef.signature.name.

</p>

<p>
Each function also needs annotations giving the location of
live pointers in its arguments, results, and local stack frame.
For an assembly function with no pointer results and
either no local stack frame or no function calls,
the only requirement is to define a Go prototype for the function
in a Go source file in the same package. The name of the assembly

In this case, the task function will write to a file (simulating sending an email).

And as the write operation doesn't use `async` and `await`, we define the function with normal `def`:

{* ../../docs_src/background_tasks/tutorial001.py hl[6:9] *}

## Add the background task

    return {"fresh_value": fresh_value}
```

////

## Recap

Apart from all the fancy words used here, the **Dependency Injection** system is quite simple.

Just functions that look the same as the *path operation functions*.

But still, it is very powerful, and allows you to declare arbitrarily deeply nested dependency "graphs" (trees).

/// tip

All this might not seem as useful with these simple examples.

  Define(1, {add}, {feed1, feed2}, {add, scalar}, {}, true);
  EXPECT_EQ(TF_INVALID_ARGUMENT, TF_GetCode(s_));
  EXPECT_EQ(string("TF_Output scalar:0 is neither in the function body nor "
                   "among function inputs. Encountered while creating "
                   "function 'MyFunc'"),
            string(TF_Message(s_)));
}

void DefineFunction(const char* name, TF_Function** func,

//          automatic skipping of dummy input operations is performed.
//  ninputs - number of elements in `inputs` array
//  inputs - array of TF_Outputs that specify the inputs to the function.
//           If `ninputs` is zero (the function takes no inputs), `inputs`
//           can be null. The names used for function inputs are normalized

# Dependencies in path operation decorators

In some cases you don't really need the return value of a dependency inside your *path operation function*.

Or the dependency doesn't return a value.

But you still need it to be executed/solved.

For those cases, instead of declaring a *path operation function* parameter with `Depends`, you can add a `list` of `dependencies` to the *path operation decorator*.