Mapytex/expression.py

#!/usr/bin/env python
# encoding: utf-8


class Expression(object):
    """A calculus expression. Today it can andle only expression with numbers later it will be able to manipulate unknown"""

    priority = {"*" : 3, "/": 3, "+": 2, "-":2, "(": 1}

    def __init__(self, exp):
        """ Initiate the expression

        :param exp: the expression. It can be a string or a list of tokens. It can be infix or postfix expression
        """
        self._exp = exp

    def simplify(self):
        """ Generator which return steps for computing the expression """
        if self._exp == 0:
            yield "Zero!"
        else:
            self.children = Expression(self._exp - 1)
            yield "num: " + str(self._exp)
            yield self.children.simplify().next()

    ## ---------------------
    ## String parsing

    ## @classmethod ????
    #def parseExp(self, exp):
    #    """ Parse the expression, ie tranform a string into a list of tokens

    #    :param exp: The expression (a string)
    #    :returns: list of token

    #    """
    #    return exp.split(" ")

    ## ---------------------
    ## "fix" recognition

    #def get_fix(self, tokens):
    #    """ Give the "fix" of an expression
    #    infix -> A + B
    #    prefix -> + A B
    #    postfix -> A B +

    #    :param exp: the expression (list of token)
    #    :returns: the "fix" (infix, postfix, prefix)

    #    """
    #    if tokens[0] in  "+-*/":
    #        return "prefix"
    #    elif token[0] not in "+-*/" ans token[1] not in "+-*/":
    #        return "postfix"
    #    else:
    #        return "infix"

    ## ----------------------
    ## Expressions - tokens getters

    #def tokens(self, fix = "infix"):
    #    """Get the list of tokens with the wanted fix

    #    :param fix: the fix wanted (infix default)
    #    :returns: list of tokens

    #    """
    #    # Si ce fix n'a pas encore été enregistré
    #    if fix not in self._tokens:
    #        # Il peut venir de la version string
    #        if fix in self._string:
    #            self._tokens[fix] = self.parseExp(self._string[fix])
    #        # Sinon il faut le calculer à partir d'une autre forme
    #        else:
    #            fix_transfo = "to" + fix.capitalize()
    #            getattr(self,fix_transfo)()

    #    return self._tokens[fix]

###### On en est là,il faudra faire attention à bien vérifier ce que les "to..." enregistre (string ou tokens)  

    #def string(self, fix = "infix"):
    #    """Get the string with the wanted fix

    #    :param fix: the fix wanted (infix default)
    #    :returns: the string representing the expression

    #    """
    #    # Si ce fix n'a pas encore été enregistré
    #    if fix not in self._string:
    #        # Il peut venir de la version string
    #        if fix in self._tokens:
    #            self._string[fix] = self.parseExp(self._string[fix])
    #        # Sinon il faut le calculer à partir d'une autre forme
    #        else:
    #            fix_transfo = "to" + fix.capitalize()
    #            getattr(self,fix_transfo)()

    #    return self._string[fix]
    #
    ## ----------------------
    ## "fix" tranformations

    #def toPostfix(self):
    #    """ Transorm the expression into postfix form using the infix form"""
    #    pass

    #def toInfix(self):
    #    """ Tranform the expression into infix form using postfix form"""
    #    pass

    ## ---------------------
    ## Tools for placing parenthesis in infix notation

    #def needPar(operande, operator, posi = "after"):
    #    """ Says whether or not the operande needs parenthesis

    #    :param operande: the operande
    #    :param operator: the operator
    #    :param posi: "after"(default) if the operande will be after the operator, "before" othewise
    #    :returns: bollean
    #    """
    #    if isNumber(operande) and "-" in operande:
    #        return 1
    #    elif not isNumber(operande):
    #        # Si c'est une grande expression ou un chiffre négatif
    #        stand_alone = get_main_op(operande)
    #        # Si la priorité de l'operande est plus faible que celle de l'opérateur
    #        minor_priority = self.priority[get_main_op(operande)] < self.priority[operator]
    #        # Si l'opérateur est -/ pour after ou juste / pour before
    #        special = (operator in "-/" and posi == "after") or (operator in "/" and posi == "before")

    #        return stand_alone and (minor_priority or special)
    #    else:
    #        return 0
    #
# J'#aime pas bien cette endroit faudrait que ce soit une méthode qui s'applique uniquement à l'expression en question (self) pas à n'importe quel string, ça serait plus propre.
    #def get_main_op(exp):
    #    """ Gives the main operation of the expression

    #    :param exp: the expression
    #    :returns: the main operation (+, -, * or /) or 0 if the expression is only one element

    #    """
    #    parStack = Stack()
    #    tokenList = exp.split(" ")

    #    if len(tokenList) == 1:
    #    # Si l'expression n'est qu'un élément
    #        return 0

    #    main_op = []

    #    for token in tokenList:
    #        if token == "(":
    #            parStack.push(token)
    #        elif token == ")":
    #            parStack.pop()
    #        elif token in "+-*/" and parStack.isEmpty():
    #            main_op.append(token)

    #    return min(main_op, key = lambda s: priority[s])

    ## ---------------------
    ## Computing the expression

    #def compute(self):
    #    """ Recursive method for computing as a student the expression
    #    :returns: list of steps needed to reach the result

    #    """
    #    pass
    #
    #def doMath(op, op1, op2):
    #    """Compute "op1 op op2"

    #    :param op: operator
    #    :param op1: first operande
    #    :param op2: second operande
    #    :returns: string representing the result

    #    """
    #    return str(eval(op1 + op + op2))

if __name__ == '__main__':
    a = Expression(10)
    for i in a.simplify():
        print(i)

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