What is positional argument self?

[Axel_Erfurt]

Your indentation is wrong, that's the problem.

from tkinter import *
 
 
class Temperature:
 
    def __init__(self):
     self.valeur = 0
 
 
    def conversionF(self):     
        result = float((9 * float(entree.get()) / 5 + 32))
        resultat.configure(text=str(result))
          
    def conversionC(self):    
        result = float((float(entree.get() - 32) * 5 / 9))
        resultat.configure(text=str(result))
 
t = Temperature()
fen1 = Tk()
fen1.title('Conversion')
 
txt1 = Label(fen1, text='Température en Fahrenheit')
txt1.grid(row=0, column=0, sticky=E)
 
entree = Entry(fen1)
entree.grid(row=0, column=1)
 
txt2 = Label(fen1, text='Température en Celcius')
txt2.grid(row=1, column=0, sticky=E)
 
resultat = Label(fen1, text='')
resultat.grid(row=1, column=1)
 
bouton = Button(fen1, text='Conversion', command=t.conversionF)
bouton.grid(row=2, column=0)

 
fen1.mainloop()