字典映射不起作用python

Question

I am writing a lexer for my compiler.There is a function to map appropriate values when we input a token.But getting the error:

[pylint] E0001:invalid syntax (, line 28)

Lexer.py

class Token(object):
    ILLEGAL_TOKEN = -1
    TOKEN_PLUS = 1
    TOKEN_MULT = 2
    TOKEN_DIV = 3
    TOKEN_SUB = 4
    TOKEN_OPEN_PAREN = 5
    TOKEN_CLOSE_PAREN = 6
    TOKEN_DOUBLE = 7
    TOKEN_NULL = 8

class Lexer(object):
    @classmethod
    def __init__(self, Expression):
        self.IExpression = Expression
        self.length = len(Expression)
        self.index = 0
        self.number = None
    @staticmethod
    def get_token(self):
        token = Token.ILLEGAL_TOKEN
        while self.index < self.length and (self.IExpression[self.index] == '' or self.IExpression[self.index] == '\t'):
            self.index += 1
        if self.index == self.length:
            return Token.TOKEN_NULL
        t = self.IExpression[self.index]

        switchCase = {
            '+' : token = Token.TOKEN_PLUS, self.index += 1,
            '-' : token = Token.TOKEN_SUB, self.index += 1,
            '*' : token = Token.TOKEN_MULT, self.index += 1,
            '/' : token = Token.TOKEN_DIV, self.index += 1,
            '(' : token = Token.TOKEN_OPEN_PAREN, self.index += 1,
            ')' : token = Token.TOKEN_CLOSE_PAREN, self.index += 1
        }
        return switchCase.get(t)

Answer 1

The value of a dictionary entry, like any value, has to be an expression which evaluates to a result (and the creators of Python made sure that you cannot assign and return a value at the same time). So assignment statements don't qualify.

You could put a function (like a lambda or like in this Q&A: Python switch case ) as value and call it when you get it, but in your case there's a better & simpler equivalent solution:

    switchCase = {
        '+' : Token.TOKEN_PLUS,
        '-' : Token.TOKEN_SUB,
        ...
    }
    token = switchCase.get(t)
    if token is not None:
       self.index += 1
    return token

So if the token is in the dict, you get your enumerate value and you can increase your index there (since you do it in all "cases" anyway)