Add the following code, again below the existing code in app.py.
python
ticks = [float(x)/10 for x in range(10,80,5)]
chart = alt.Chart(filtered_data).mark_point().encode(
    x=alt.X('num_rooms', axis=alt.Axis(values=ticks)),
    y='price',
    color='city',
    tooltip=['description', 'post_code', 'Size', 'Price']
).interactive()
st.altair_chart(chart)
Streamlit provides some higher-level convenience functions around the plotting library Altair, but we want to customize some aspects so we will drop down a layer and use the Altair API directly.
There aren't any properties with more than 8 rooms in our dataset, so we will hardcode the chart to show a range from 1 room to 8 rooms on the X axis. Swiss properties also often have 'half' rooms - a large hallway or kitchen is often counted as a 'half' room, so we will create a range from [1.0, 1.5, 2.0 ... 7.5, 8.0] to set our X ticks.
