Mapytex/expression.py

148 lines
3.9 KiB
Python

#!/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"""
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._tokens = {}
self._strings = {}
if type(exp) == list:
fix = self.get_fix(exp)
self._tokens[fix] = exp
elif type(exp) == str:
tokens = self.parseExp(exp)
fix = self.get_fix(tokens)
self._tokens[fix] = tokens
self._strings[fix] = exp
else:
raise ValueError("The expression needs to be a string or a list of token")
# ---------------------
# 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
"""
if fix not in self._tokens:
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
"""
if fix in self._string:
return self._string[fix]
else:
pass
# ----------------------
# "fix" tranformations
def toPostfix(self):
""" Transorm the expression into postfix form """
pass
def toInfix(self):
""" Tranform the expression into infix 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
"""
pass
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
"""
pass
# ---------------------
# 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))
# -----------------------------
# Reglages pour 'vim'
# vim:set autoindent expandtab tabstop=4 shiftwidth=4:
# cursor: 16 del