Function running without clicking the Python button

Question

Good night, My callbackInsereCritico function runs straight without the click of the button, which may be?

def callbackInsereCritico(nome):
  conn = psycopg2.connect(host='localhost',
                        database='diet+',
                        user='postgres',
                        password='teste')

  cur = conn.cursor()
  curCritics = conn.cursor()
  cur.execute("INSERT INTO critico (nome) VALUES ('" + nome + "')")                              
  conn.commit() 



rotuloAv = Label(formulario, text = "Cadastro do Avaliador")
rotuloNm = Label(formulario, text = "Nome:")
texto9 = Entry(formulario)
botaoAv =  Button(formulario, text = "Cadastrar",command = callbackInsereCritico(texto9.get())) 
resultadoAv = Label(formulario, text = None)

Answer 1

You’re not passing a function the way you’re doing. Instead, you are running the function callbackInsereCritico and passing the return value to the attribute command. That’s why it’s running without the click event.

Imagine you have this function:

def fazalgo():
    return "fizalgo"

If you run:

type(fazalgo)

The comeback will be:

<type 'function'>

Now, if you execute:

type(fazalgo())

The comeback will be:

<type 'str'>

Did you notice the difference? In the first case, the function type received as parameter a function, already in the second, received the return of the function.

Now, as you need to pass an argument to the function, you can’t just do: command = callbackInsereCritico.

Has a pythonic way of doing that:

command = lambda: callbackInsereCritico(texto9.get())

lambda in Python is nothing more than an elegant way of declaring functions. They are very useful for certain moments, such as this.

So your code stays:

def callbackInsereCritico(nome):
  conn = psycopg2.connect(host='localhost',
                        database='diet+',
                        user='postgres',
                        password='teste')

  cur = conn.cursor()
  curCritics = conn.cursor()
  cur.execute("INSERT INTO critico (nome) VALUES ('" + nome + "')")                              
  conn.commit() 



rotuloAv = Label(formulario, text = "Cadastro do Avaliador")
rotuloNm = Label(formulario, text = "Nome:")
texto9 = Entry(formulario)
botaoAv =  Button(formulario, text = "Cadastrar", command = lambda: callbackInsereCritico(texto9.get()))
resultadoAv = Label(formulario, text = None)

How to explain lambda here departs from the scope of the question, I leave here this link: http://blog.alienretro.com/entendendo-python-lambda/