I can not execute the code because PyCharm says that the App class was not created

PyCharm says that the App class has not been defined, but that does not make sense since I created the App class.

from tkinter import *
class App:
    def __init__(self,master):
        frame = Frame(master)
        frame.pack()
        Label(frame,text='Graus C').grid(row=0)
        self.c_var = DoubleVar()
        Entry(frame, textvariable=self.c_var).grid(row=0,column=1)
        Label(frame,text='Graus F').grid(row=1)
        self.result_var = DoubleVar()
        Label(frame,textvariable=self.result_var).grid(row=1,column=1)
        button = Button(frame,text='Convert',command=self.convert).grid(row=2,columnspan=2)

    def convert(self):
        print('No implemented')

root = Tk()
root.wm_title('Conversor de graus C para graus F')
app = App(root)
root.mainloop()

Error:

Traceback (most recent call last):
  File "D:\PyCharm Community Edition 2018.1.4\helpers\pydev\pydev_run_in_console.py", line 52, in run_file
    pydev_imports.execfile(file, globals, locals)  # execute the script
  File "D:\PyCharm Community Edition 2018.1.4\helpers\pydev\_pydev_imps\_pydev_execfile.py", line 18, in execfile
    exec(compile(contents+"\n", file, 'exec'), glob, loc)
  File "C:/Users/nicol/PycharmProjects/Projetos/converter.py", line 2, in <module>
    class App:
  File "C:/Users/nicol/PycharmProjects/Projetos/converter.py", line 19, in App
    app = App(root)
NameError: name 'App' is not defined