Recuperer la valeur d'une fonction

Matrix = [[0 for x in xrange(10)] for x in xrange(10)]
x=4 #Coordonnee en x egal ind_ic
y=4 #Coordonnee en y egal a p et ind_jc 
r=2 #rayon de couverture
SN=0 #Difference entre Nord et Sud

def maj():
 Matrix[4][2]=1 #West"
 Matrix[4][4]=5 #Centre de matrice noeud"
 Matrix[4][6]=3 #East"
 Matrix[2][4]=2 #"Nord
 Matrix[6][4]=4 #"South

def show():
 for line in Matrix:
  print line
 return line

def nord():
 global x
 global y
 global r
 Cn=0
 i=0
 i=y-r
 for somme in range(len(Matrix)):
  if i <= (y+r):
   Cn+=Matrix[2][i]
   i+=1
 return Cn

def south():
 global x
 global y
 global r
 Cs=0
 i=0
 i=y-r
 for somme in range(len(Matrix)):
  if i <= (y+r):
   Cs+=Matrix[6][i]
   i+=1
 return Cs

maj()
show()
nord()
south()
SN=(int(Cn)-int(Cs))**2