PythonExpressionInterpreter/parser_.py at main · BaseMax/PythonExpressionInterpreter · GitHub

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fromtokensimportTokenType
fromnodesimport*

classParser:
def__init__(self, tokens):
self.tokens=iter(tokens)
self.advance()

defraise_error(self):
raiseException("Invalid syntax")

defadvance(self):
try:
self.current_token=next(self.tokens)
exceptStopIteration:
self.current_token=None

defparse(self):
ifself.current_token==None:
returnNone

result=self.expr()

ifself.current_token!=None:
self.raise_error()

returnresult

defexpr(self):
result=self.term()

whileself.current_token!=Noneandself.current_token.typein (TokenType.PLUS, TokenType.MINUS):
ifself.current_token.type==TokenType.PLUS:
self.advance()
result=AddNode(result, self.term())
elifself.current_token.type==TokenType.MINUS:
self.advance()
result=SubtractNode(result, self.term())

returnresult

defterm(self):
result=self.factor()

whileself.current_token!=Noneandself.current_token.typein (TokenType.MULTIPLY, TokenType.DIVIDE):
ifself.current_token.type==TokenType.MULTIPLY:
self.advance()
result=MultiplyNode(result, self.factor())
elifself.current_token.type==TokenType.DIVIDE:
self.advance()
result=DivideNode(result, self.factor())

returnresult

deffactor(self):
token=self.current_token

iftoken.type==TokenType.LPAREN:
self.advance()
result=self.expr()

ifself.current_token.type!=TokenType.RPAREN:
self.raise_error()

self.advance()
returnresult

eliftoken.type==TokenType.NUMBER:
self.advance()
returnNumberNode(token.value)

eliftoken.type==TokenType.PLUS:
self.advance()
returnPlusNode(self.factor())

eliftoken.type==TokenType.MINUS:
self.advance()
returnMinusNode(self.factor())

self.raise_error()