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from flask import Flask
    
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app = Flask(__name__)
    
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@app.route('/')
def hello_world():
    return 'Hello, World'
    
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app.run()
    
(for NIX)
\$ export FLASK_APP=hello.py  
(for Windows)  
\$ set FLASK_APP=hello.py
\$ flask run
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app.run(host='localhost', port='5001')
    
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