pythonBytes/evalPostFix.py at master · bourneagain/pythonBytes · GitHub

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#for prefix expression evalution : same as postfix
#just reverse and use the same : only in / and - use a and b the other way that not a-b but b-a
defevalPost(postfix):
res=[]
op=[]
foriinpostfix:
ifi.isdigit():
print"entering "+str(i)
res.append(i)
else:
print"entering operator"+str(i)
op.append(i)
print"len of op"+str(len(op))
iflen(op) >0:
print"popping"
b=int(res.pop())
a=int(res.pop())
printa,b
ifi=="*": c=int(a*b)
ifi=="+": c=int(a+b)
ifi=="-": c=int(a-b)
printc
res.append(c)
returnres,op

defevalPre(prefix):
prefixList=[]
foriinprefix:
prefixList.append(i)
prefixList.reverse()
printprefixList
returnevalPost(prefixList)

#https://www.youtube.com/watch?v=MeRb_1bddWg

postfix="23*52*+"
prefix="-+*23*549"
printevalPost(postfix)
#print evalPre(prefix)
#5 2
#10
#3 10
#13
#['2', 13]