Python: Error: "function" object is not iterable

I am doing a program that opens a txt, it loads several fields: IDquestion, Question, Answer, AnswerDate and At. In the txt the fields are separated with a "^". I have an error in a function called "Savevalues", to which I associate a button. What this function intends to do is save the values that the user puts in three text fields corresponding to IDquestion, Question and Answer in a txt aided by two functions: "Entitylist_matrix" and "save", when the button is pressed.

def Savevalues():
    IDQuestionlist, Questionlist, Answerlist, AnswerDatelist, Atlist = Entitylist_matrix
    IDQuestionlist = IDQuestionlist + [entryIDquestion.get()]
    Questionlist = Questionlist + [entryQuestion.get()]
    Answerlist = Answerlist + [entryAnswer.get()]
    AnswerDatelist = AnswerDatelist + [0] #Le meto un cero por defecto
    Atlist = Atlist + [0] #Le pongo un cero por defecto
    save

When I run, I get an error in that function that says:

  

'"function" object is not iterable'

It seems that the problem is in a line that is:

IDQuestionlist, Questionlist, Answerlist, AnswerDatelist, Atlist = Entitylist_matrix

Can not I call a function within another function? o Can I not return variables from another function within a function?

#CARGAMOS LOS DATOS
#Abrimos el archivo
#Pasamos el archivo de txt a formato de listas de entidad.
def txt_Entitylist():
    f = open("Questions CE.txt","r")
    filechain = f.read()
    #Atención! Asegurate que no hay un caracter EOF después del ultimo "0"
    #Saco Entitylist
    Entitylist = []
    Entitylist = filechain.split("|")
    f.close()
    return Entitylist

#Función para convertir un txt en una matriz

def Entitylist_matrix():
    Entitylist = txt_Entitylist()
    #Partimos Entitylist en una lista de palabras (wordlist)
    wordlist = []
    partx = []
    for x in Entitylist:
        partx = x.split("^")
        a = 0
        while a < len(partx):
            wordlist = wordlist + [partx[a]]
            a = a + 1
    #IDQuestionlist
    IDQuestionlist = []
    i = 0
    while i<len(wordlist):
        IDQuestionlist = IDQuestionlist + [wordlist[i]]
        i = i + 5
    #Questionlist
    Questionlist = []
    i = 1
    while i<len(wordlist):
        Questionlist = Questionlist + [wordlist[i]]
        i = i + 5
    #Answerlist
    Answerlist = []
    i = 2
    while i<len(wordlist):
        Answerlist = Answerlist + [wordlist[i]]
        i = i + 5
    #AnswerDatelist
    AnswerDatelist = []
    i = 3
    while i<len(wordlist):
        AnswerDatelist = AnswerDatelist + [wordlist[i]]
        i = i + 5
    #Atlist (Delta time)
    Atlist = []
    i = 4
    while i<len(wordlist):
        Atlist = Atlist + [wordlist[i]]
        i = i + 5
    return IDQuestionlist, Questionlist, Answerlist, AnswerDatelist, Atlist


#Función que guarda los datos
def matrix_txt(IDQuestionlist, Questionlist, Answerlist, AnswerDatelist, Atlist):
    file=open('Questions CE.txt','w') #Si lo abres en modo "a", añade datos sin borrar los que ya estaban
    #1º Quitamos los espacios en blanco que nos sobran de AnswerDatelist y Atlist
    #i = 0
    #while i<len(Atlist):
    #    a = str(Atlist[i])
    #    Atlist[i] = a.strip()
    i = 0
    while i<len(Atlist):
          file.write(""+IDQuestionlist[i]+""+"^")
          file.write(""+Questionlist[i]+""+"^")
          file.write(""+Answerlist[i]+""+"^")
          file.write(" "+str(AnswerDatelist[i]).strip()+" "+"^")
          if i + 1 == len(Atlist):
              file.write(" "+str(Atlist[i]).strip()+" ")
          else:
              file.write(" "+str(Atlist[i]).strip()+" "+"^")
          i = i + 1
    file.close()

#Función para guardar datos desde línea de comandos
def save():
    matrix_txt(IDQuestionlist, Questionlist, Answerlist, AnswerDatelist, Atlist)



def Savevalues():
    IDQuestionlist, Questionlist, Answerlist, AnswerDatelist, Atlist = Entitylist_matrix
    IDQuestionlist = IDQuestionlist + [entryIDquestion.get()]
    Questionlist = Questionlist + [entryQuestion.get()]
    Answerlist = Answerlist + [entryAnswer.get()]
    AnswerDatelist = AnswerDatelist + [0] #Le meto un cero por defecto
    Atlist = Atlist + [0] #Le pongo un cero por defecto
    save


#Creando una ventanta principal
window=tk.Tk()
window.geometry("500x300+100+100")
window.title("Question Editor")

#Creamos un frame como contenedor
frame = tk.Frame(window)

#Creando un campo de texto para question
entryQuestion=tk.StringVar()
entryQuestion.set("")
txtQuestion=tk.Entry(frame,textvariable=entryQuestion)
txtQuestion.grid(row=0, column=1)

#Creando un campo de texto para answer
entryAnswer=tk.StringVar()
entryAnswer.set("")
txtAnswer=tk.Entry(frame,textvariable=entryAnswer)
txtAnswer.grid(row=1, column=1)

#Creando un campo de texto para IDquestion
entryIDquestion=tk.StringVar()
entryIDquestion.set("")
txtIDquestion=tk.Entry(frame,textvariable=entryIDquestion)
txtIDquestion.grid(row=2,column=1)

#Creando un label para el campo de texto "question"
labelQuestion = tk.Label(frame, text="Question", padx=10 )
labelQuestion.grid(row=0, column=0, sticky=tk.W)

#Creando un label para el campo de texto "answer"
labelAnswer = tk.Label(frame, text="Answer", padx=10 )
labelAnswer.grid(row=1, column=0, sticky=tk.W)

#Creando un label para el campo de texto "IDquestion"
labelIDquestion = tk.Label(frame, text="IDquestion", padx=10)
labelIDquestion.grid(row=2, column=0, sticky=tk.W)

#Definimos un tamaño mínimo de la fila central delgrid para que quede un espacio entre cada entry y posicionamos el frame
frame.grid_rowconfigure(1, minsize=10)
frame.place(x=0,y=140)

#Creando un botón para guardar pregunta y respuesta
btnSave=tk.Button(window,text="Save",command=Savevalues,font=("Agency FB",14))
btnSave.place(x=130,y=210)

#Iniciamos el mailoop
window.mainloop()

#Programa
Entitylist_matrix