Duplicate Callback Output error in dash app - python-3.x

Question

I am getting an error in dash app. The error: "You have already assigned a callback to the output with the ID "prediction" and property "children". An output can only have a single callback function. Try combining your inputs and callback functions together into one function."
I have only one callback function in my code.
How to resolve this?
My code below:
model_data = pd.read_csv("data.csv")
style = {'padding': '1.5em'}
app.layout = html.Div([
dcc.Markdown("""
### Predict
"""),
html.Div(id='prediction-content', style={'fontWeight': 'bold'}),
html.Div([
dcc.Markdown('###### Input1'),
dcc.Dropdown(
id='Input1',
options=[{'label': 1, 'value': 1}],
value= 1
),
], style=style),
html.Div([
dcc.Markdown('###### Input2'),
dcc.Slider(
id='Input2',
min=23,
max=27,
step=0.5,
value=23,
tooltip={'always_visible': True},
marks={
23: {'label': '23'},
24: {'label': '24'},
25: {'label': '25'},
26: {'label': '26'}
},
included=False
)
], style=style),
html.Div([
dcc.Markdown('###### Input3'),
dcc.Slider(
id='Input3',
min=10,
max=50,
step=1,
value=30,
tooltip={'always_visible': True},
marks={
10: {'label': '10'},
20: {'label': '20'},
30: {'label': '30'},
40: {'label': '40'},
50: {'label': '50'}
},
included=False
)
], style=style),
])
#app.callback(
Output('prediction-content', 'children'),
[Input('Input1', 'value'),
Input('Input2', 'value'),
Input('Input3', 'value')])
def predict(a, b, c):
data2 = pd.DataFrame(data = [[a, b, c,]],
columns = ['Input1', 'Input2','Input3']
, index = [36])
data3 = model_data.combine_first(data2)
#### full function hidden due to confidentiality
def calculate(df,i,j):
###
####
return(a1)
output = a1*2
results = f'Result is ${output:,.0f}.'
return results
if __name__ == '__main__':
app.run_server(debug=True)

Answer 1

i had the same issue using Jupiter notebook but solved it by killing the server and restarting my kernel, i assume that the callback assigns the function once and if you try to re-assign it again it will through that error. I guess this error will be thrown only when you are using hot reloading.