How to access immediate character of string in python -


i'm working on small program removes unit production in given grammar. i've developed 1 logic correct me. problem i'm facing cannot access next immediate index of string stored in list in python.

gram=[line.rstrip('\n') line in open("grammar.txt","r+")]  non_terminals=[] productions=[] item in range(len(gram)):    non_terminals.append(gram[item][0])     print(non_terminals)    temp=[] item in range(len(gram)):    str in non_terminals:      if gram[item][0] str:         productions.append(gram[item].lstrip(str).lstrip('-'+'>'))    temp=''  item in range(len(productions)):    str in range(len(productions[item])):        nt in non_terminals:           if productions[item][str] nt:              if productions[item][str-1] '|' , (productions[item]  [str+1] '|'):                  i=nt.index(nt)                  temp=productions[item].rstrip(nt)                  temp=temp+productions[i]    print(productions)   print(temp)

i'm getting error

if productions[item][str-1] '|' , (productions[item][str+1] '|'): indexerror: string index out of range

text file contains

s->s+t|t t->t*f|f f->(s)|a

can suggest reason i'm not able so.?


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