Refer to a widget outside the class - Tkinter - Python3.6

I have an application where I have my main code in a file called main.py and the functions and classes in another file called events.py. Well I have a class like this and what happens to me is that anywhere in the code I can put self.label and I refer to a label of my application, which is created in main.py, but within this class if I put self.label throws me an error because it seems that self in this case is the class itself or something like that. How can I refer to a widget from within this class? This class what it does is show a dataframe in a TreeView widget and I want in the process of creating the table to change an image that I have in a label.

class DataFrameTreeView(tk.Frame):

 def __init__(self, *args, **kwargs):
   super().__init__(*args, **kwargs)
   self.config(bg="#FFF4DC")
   self.tree_view = None
   self.hscrollbar = None
   self.vscrollbar = None
   self._data = None

 def load_table(self, df, columns=None, columns_headers=None, chunk_size=20):

   """
   Args:
       path: cadena -> ruta al fichero .xlsx
       columns: list -> columnas a mostrar en la tabla, si es None se,muestran todas
       columns_headers: list -> Nombres para las cabeceras de las columnas,
                                si es None se usan las cabeceras del DataFrame

       chunk_size: int -> Número de filas creadas por iteración
   """ 

   if columns is not None:
       dif = set(columns) - set(df.columns)
       if dif:
           raise ValueError(f"Columns: {tuple(dif)} are not in DataFrame") 
   else:
       columns = df.columns

   if columns_headers is not None:
       if  len(columns_headers) != len(df.columns):
           raise ValueError("headers length not mismath columns number")
   else:
       columns_headers = columns
   tk_col_names =[f"#{name}" for name in columns_headers]

   # Treeview y barras
   if self.tree_view is not None:
       self.tree_view.destroy()
       self.hscrollbar.destroy()
       self.vscrollbar.destroy()

   self.tree_view = ttk.Treeview(self, columns=tk_col_names)
   self.vscrollbar = ttk.Scrollbar(self, orient='vertical', command = self.tree_view.yview)
   self.vscrollbar.pack(side='right', fill=tk.Y)
   self.hscrollbar = ttk.Scrollbar(self, orient='horizontal', command = self.tree_view.xview)
   self.hscrollbar.pack(side='bottom', fill=tk.X)
   self.tree_view.configure(yscrollcommand=self.vscrollbar.set)
   self.tree_view.configure(xscrollcommand=self.hscrollbar.set)

   w=self.winfo_reqwidth()     

   # Configuar columnas y cabeceras
   for name, header, col in zip(tk_col_names, columns_headers,  columns):
       self.tree_view.column(name, anchor='c', width=round(w*0.3), stretch=True, minwidth=120)

   self.tree_view['show'] = 'headings'

   # Cargamos los items
   rows = df.shape[0]
   chunks = rows / chunk_size
   progress = 0
   step = 100 / chunks

   arial14 = font.Font(family='Arial', size=14)
   progress_bar = ttk.Progressbar(self, orient="horizontal",
                                   length=100, mode="determinate")
   label_value = tk.StringVar(value="Loading...")
   progress_bar["value"] = progress 
   label = tk.Label(self, textvariable=label_value, font=arial14, bg="#FFF4DC")
   label.place(relx=0.50, rely=0.4, anchor=tk.CENTER)
   progress_bar.place(relx=0.5, rely=0.5, relwidth=0.80,  anchor=tk.CENTER)

   for ind in df.index:
       if ind > 0.25*rows:
           label_value.set("Reading File...")
       if ind > 0.50*rows:
           label_value.set("Preprocessing...")
       if ind > 0.80*rows:
           label_value.set("Analyzing...")
       values = [str(v) for v in df.loc[ind, columns].values]
       self.tree_view.insert("", tk.END, text=ind+1, values=values)
       if ind % chunk_size == 0:
           self.update_idletasks()
           progress += step
           progress_bar["value"] = progress 

   progress_bar["value"] = progress
   self.update_idletasks()

   progress_bar.destroy()
   label.destroy()
   self.tree_view.pack(expand=True, fill='both')

   self._data = df[columns].copy()
   # Creamos columna en dataframe local con los items
   self._data.columns = tk_col_names
   self._data["#iids"] = self.tree_view.get_children('')