CPM Buffer Timer calculation

#!/usr/bin/env python
__author__ = "Jiezheng Zhang"
__copyright__ = "Copyright 2014, Jiezheng Zhang"
__credits__ = ["Jiezheng (Sebastian) Zhang", "Altan Karakul", "Yusuf Azal","Wassilij Mikheyev"]
__license__ = "GPL"
__version__ = "1.0.0"
__email__ = "jiezheng.zhang@gmail.com"

import math,sys

D ={0:{1:8,5:16},
1:{2:8,3:16,4:16},
2:{8:20},
3:{8:12},
4:{7:16},
5:{6:36},
6:{7:0,8:0},
7:{9:12},
8:{9:12},
9:{10:8},
10:{11:8},
11:{12:2},
12:{}
}

T = sys.maxint
Debug = True
#####################################
#Schritt 1 Init
M = [0]
FZ = [0 for x in xrange(len(D))]
DeltaPlus = [0 for x in xrange(len(D))]
DeltaMinus = [0 for x in xrange(len(D))]
for i in D:
    DeltaPlus[i]=len(D[i].keys())
DeltaPlus[0]=0


for k in D.keys():
    for i in D[k]:
        DeltaMinus [i] +=1
if Debug:
    print "DeltaMinus", DeltaMinus
    print "DeltaPlus", DeltaPlus

#invertiere D zu Vorgaenger Dictionary P
#P[j][i] == Z[i][j]
P={0:{}}
for i in D:
    for j in D[i]:
        if not P.has_key(j):
            P[j] = {}
        P[j][i] = D[i][j]

#Schritt 2 (Vorwaertsrechnung):
while M:
    k = M.pop()
    #print k
    zyklen = True
    for i in D[k].keys():
        DeltaMinus[i]-=1
        if DeltaMinus[i] == 0:
                M.append(i)
                zyklen = False
        if FZ[k]+D[k][i]> FZ[i]:
                FZ[i] = FZ[k]+D[k][i]
    #print FZ
    if zyklen == True:
        print "Zyklen! k:{}\t D[k]:{}\t DeltaMinus[k]:{}".format( k,D[k],DeltaMinus[k])
        #sys.exit()

for fzn in FZ:
    if T< fzn:
        print "Projektendtermin kann nicht gehalten werden."
        sys.exit()

print "FZ", FZ
#Schritt 3 (Rueckwaertsrechnung):
M=[len(D)-1]
SZ = [ FZ[-1] for x in xrange(len(D))]

while M:
    k = M.pop()
    #print k
    zyklen = True
    for i in D.keys():
        if k in D[i]:
            DeltaPlus[i]-=1
            if DeltaPlus[i] == 0:
                    M.append(i)

            if SZ[k]-D[i][k]< SZ[i]:
                    SZ[i] = SZ[k]-D[i][k]
    #print SZ
        #sys.exit()
print "SZ", SZ

####################################################
#Puffer

#Init
FAZ = [[0 for x in xrange(len(D))] for x in xrange(len(D))]
FEZ = [[0 for x in xrange(len(D))] for x in xrange(len(D))]
SAZ = [[0 for x in xrange(len(D))] for x in xrange(len(D))]
SEZ = [[0 for x in xrange(len(D))] for x in xrange(len(D))]
GP  = [[0 for x in xrange(len(D))] for x in xrange(len(D))]
FP  = [[0 for x in xrange(len(D))] for x in xrange(len(D))]
FRP = [[0 for x in xrange(len(D))] for x in xrange(len(D))]
UP  = [[0 for x in xrange(len(D))] for x in xrange(len(D))]

#calc
for i in D.keys():
    for j in D[i].keys():
        FAZ[i][j] = FZ[i]
        FEZ[i][j] = FZ[i]+D[i][j]
        SAZ[i][j] = SZ[j]-D[i][j]
        SEZ[i][j] = SZ[j]
        GP[i][j] = SAZ[i][j] -  FAZ[i][j]
        FP[i][j] = FZ[j]  -  FEZ[i][j]
        FRP[i][j] = SAZ[i][j] -  SZ[i]
        UP[i][j] =max(0,FZ[j]-SZ[i]-D[i][j])

#Output
print ("FZ:")
for i in FZ:
    print i
print ("SZ:")
for i in SZ:
    print i
print ("Pfad\tD\tFAZ\tFEZ\tSAZ\tSEZ\tGP\tFP\tFRP\tUP")

for i in D.keys():
    for j in D[i].keys():
        print "<{},{}>\t{}\t{}\t{}\t{}\t{}\t{}\t{}\t{}\t{}".format(i,j,D[i][j],
                                                                max(0,FAZ[i][j]),
                                                                max(0,FEZ[i][j]),
                                                                max(0,SAZ[i][j]),
                                                                max(0,SEZ[i][j]),
                                                                max(0,GP[i][j]),
                                                                max(0,FP[i][j]),
                                                                max(0,FRP[i][j]),
                                                                max(0,UP[i][j])
                                                                )