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# coding=UTF-8
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# Relation
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# Copyright (C) 2008 Salvo "LtWorf" Tomaselli
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#
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# Relation is free software: you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation, either version 3 of the License, or
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# (at your option) any later version.
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#
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# This program is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU General Public License for more details.
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#
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# You should have received a copy of the GNU General Public License
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# along with this program. If not, see <http://www.gnu.org/licenses/>.
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#
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# author Salvo "LtWorf" Tomaselli <tiposchi@tiscali.it>
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def parse(expr):
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'''This function parses a relational algebra expression, converting it into python,
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executable by eval function to get the result of the expression.'''
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#Selection σage > 25 Λ rank = weight(A)
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#Projection π a,b(A)
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#Rename ρid➡i,name➡n(A)
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#A ᑌ B
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#A ᐅᐊ B
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#A ᑎ B
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result=""
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symbols={}
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symbols["*"]=".product(%s)"
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symbols["-"]=".difference(%s)"
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symbols["ᑌ"]=".union(%s)"
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symbols["ᑎ"]=".intersection(%s)"
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symbols["ᐅᐊ"]=".join(%s)"
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symbols["ᐅᐊLEFT"]=".outer_left(%s)"
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symbols["ᐅᐊRIGHT"]=".outer_right(%s)"
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symbols["ᐅᐊFULL"]=".outer(%s)"
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tokens=expr.split(" ")
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i=0;
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tk_l=len(tokens)
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while i<tk_l:
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if tokens[i] not in symbols:
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result+=tokens[i]
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else:
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result+=symbols[tokens[i]] % (tokens[i+1])
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i+=1
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i+=1
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return result
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if __name__=="__main__":
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while True:
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e=raw_input("Expression: ")
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print parse(e)
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