Howto - Python yield statement

Hi folks, not sure if this is the best place to get some advice, feel free to let me know if it's not.
I'm trying to implement a Python class which has one method that uses two yield statements. My current PyCall implementation is this, but it gives me a "SyntaxError: 'yield' outside function":

```
using PyCall

textual = pyimport("textual")
pyimport("textual.app")
pyimport("textual.widgets")

@pydef mutable struct StopwatchApp <: textual.app.App
function compose(self)
py"""
yield textual.widgets.Header()
yield textual.widgets.Footer()
"""
end
end
```

The full error is this:
```
Traceback (most recent call last)
in :1

/home/name/.julia/packages/PyCall/1gn3u/src/pyeval.jl:1
const Py_single_input = 256 # from Python.h

SyntaxError: 'yield' outside function
```

`yield` doesn't seem to be discussed in PyCall's docs so I'm wondering if there's an implementation for this. Please give me a shout if you can help me out :)