116 lines
3.4 KiB
Plaintext
116 lines
3.4 KiB
Plaintext
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#!/usr/bin/env python
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# encoding: utf-8
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from generic import Stack
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from calculus import isNumber, doMath
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class Expression(object):
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"""An arithmetic expression"""
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priority = {"*" : 3, "/": 3, "+": 2, "-":2, "(": 1}
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def __init__(self, exp, fix = "infix"):
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"""Initiate the expression.
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:param exp: the string representing the expression (infx form by default)
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:param fix: form of the expression infix (default) - postfix - prefix
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"""
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if fix == "infix":
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self._exp_infix = exp
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self._token_infix = exp.split(" ")
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elif fix == "postfix":
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self._token_postfix = exp
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else:
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print("Pas encore fait!")
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def infixToPostfix(self):
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"""Convert the infix expression into postfix expression.
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"""
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#@todo importer les exemples
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opStack = Stack()
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postfixList = []
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for token in self._token_infix:
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if token == "(":
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opStack.push(token)
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elif token == ")":
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topToken = opStack.pop()
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while topToken != "(":
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postfixList.append(topToken)
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topToken = opStack.pop()
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elif token in "+-*/":
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while (not opStack.isEmpty()) and (self.priority[opStack.peek()] >= self.priority[token]):
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postfixList.append(opStack.pop())
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opStack.push(token)
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else:
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postfixList.append(token)
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while not opStack.isEmpty():
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postfixList.append(opStack.pop())
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self._token_postfix = postfixList
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self._exp_postfix = " ".join(postfixList)
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def computePostfix(self):
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"""Compute a postfix expression like a good student
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:returns: list of steps to reach the result (postfix form)
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"""
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tokenList = self._token_postfix.copy()
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tmpTokenList = []
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# on va chercher les motifs du genre A B + pour les calculer
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while len(tokenList) > 2:
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#print(tokenList[2])
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if isNumber(tokenList[0]) and isNumber(tokenList[1]) and tokenList[2] in "+-*/":
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# S'il y a une opération à faire
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op1 = tokenList[0]
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op2 = tokenList[1]
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token = tokenList[2]
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res = doMath(token, op1, op2)
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tmpTokenList.append(res)
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# Comme on vient de faire le calcul, on peut détruire aussi les deux prochains termes
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del tokenList[0:3]
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else:
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tmpTokenList.append(tokenList[0])
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del tokenList[0]
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tmpTokenList += tokenList
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if len(tmpTokenList) > 1:
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next_steps = Expression(tmpTokenList, fix = "postfix").computePostfix()
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else:
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next_steps = tmpTokenList
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print(self._exp_postfix)
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return [self._exp_postfix] + next_steps
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def test(exp):
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"""Make various test on an expression
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"""
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print("-------------")
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print("Expression ",exp)
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expression = Expression(exp)
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expression.infixToPostfix()
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print(expression.computePostfix())
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if __name__ == '__main__':
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exp = "1 + 3 * 5"
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test(exp)
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exp = "2 * 3 * 3 * 5"
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test(exp)
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exp = "2 * 3 + 3 * 5"
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test(exp)
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# -----------------------------
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# Reglages pour 'vim'
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# vim:set autoindent expandtab tabstop=4 shiftwidth=4:
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# cursor: 16 del
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