for i in range(int(st.number_input('Num:'))):
  foo()
if st.sidebar.selectbox('I:',['f']) == 'f':
  b()
my_slider_val = st.slider('Quinn Mallory', 1, 88)
st.write(slider_val)
```
Mutate data
```python
Add rows to a dataframe after
showing it.
element = st.dataframe(df1)
element.add_rows(df2)
Add rows to a chart after
showing it.
element = st.line_chart(df1)
element.add_rows(df2)
```
Display code
```python
with st.echo():
  st.write('Code will be executed and printed')
```
Placeholders, help, and options
```python
Replace any single element.
element = st.empty()
element.line_chart(...)
element.text_input(...)  # Replaces previous.
Insert out of order.
elements = st.container()
elements.line_chart(...)
st.write("Hello")
elements.text_input(...)  # Appears above "Hello".
st.help(pandas.DataFrame)
