dash_app_layout.py

import dash
import dash_core_components as dcc
import dash_html_components as html
import pandas as pd

app = dash.Dash('app', server=server)
df = pd.read_csv('input_data.csv')

# ========== App Layout ================
app.layout = html.Div([
    html.H1('Example app'),
    dcc.Dropdown(
        id='dropdown-1',
        options=[
            {'label': 'Oct 2018', 'value': '201810'},
            {'label': 'Nov 2018', 'value': '201811'},
        ],
        value='201810',
    ),
    dcc.Graph(id='line-chart-1'),
])