fc49ba5bbe
git-svn-id: http://galileo.dmi.unict.it/svn/relational/trunk@196 014f5005-505e-4b48-8d0a-63407b615a7c
298 lines
12 KiB
Python
298 lines
12 KiB
Python
# -*- coding: utf-8 -*-
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# coding=UTF-8
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# Relational
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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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RELATION=0
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UNARY=1
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BINARY=2
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b_operators=('*','-','ᑌ','ᑎ','ᐅᐊ','ᐅLEFTᐊ','ᐅRIGHTᐊ','ᐅFULLᐊ')
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u_operators=('π','σ','ρ')
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op_functions={'*':'product','-':'difference','ᑌ':'union','ᑎ':'intersection','ᐅᐊ':'join','ᐅLEFTᐊ':'outer_left','ᐅRIGHTᐊ':'outer_right','ᐅFULLᐊ':'outer','π':'projection','σ':'selection','ρ':'rename'}
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class node (object):
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'''This class is a node of a relational expression. Leaves are relations and internal nodes are operations.
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The kind property says if the node is a binary operator, unary operator or relation.
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Since relations are leaves, a relation node will have no attribute for children.
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If the node is a binary operator, it will have left and right properties.
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If the node is a unary operator, it will have a child, pointing to the child node and a prop containing
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the string with the props of the operation.
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This class is used to convert an expression into python code.'''
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kind=None
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def __init__(self,expression=None):
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'''Generates the tree from the tokenized expression
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If no expression is specified then it will create an empty node'''
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if expression==None or len(expression)==0:
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return
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#If the list contains only a list, it will consider the lower level list.
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#This will allow things like ((((((a))))) to work
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while len(expression)==1 and isinstance(expression[0],list):
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expression=expression[0]
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#The list contains only 1 string. Means it is the name of a relation
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if len(expression)==1 and isinstance(expression[0],str):
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self.kind=RELATION
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self.name=expression[0]
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return
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'''Expression from right to left, searching for binary operators
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this means that binary operators have lesser priority than
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unary operators.
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It find the operator with lesser priority, uses it as root of this
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(sub)tree using everything on its left as left parameter (so building
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a left subtree with the part of the list located on left) and doing
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the same on right.
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Since it searches for strings, and expressions into parenthesis are
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within sub-lists, they won't be found here, ensuring that they will
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have highest priority.'''
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for i in range(len(expression)-1,-1,-1):
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if expression[i] in b_operators: #Binary operator
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self.kind=BINARY
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self.name=expression[i]
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self.left=node(expression[:i])
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self.right=node(expression[i+1:])
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return
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'''Searches for unary operators, parsing from right to left'''
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for i in range(len(expression)-1,-1,-1):
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if expression[i] in u_operators: #Unary operator
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self.kind=UNARY
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self.name=expression[i]
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self.prop=expression[1+i].strip()
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self.child=node(expression[2+i])
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return
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pass
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def toPython(self):
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'''This method converts the expression into python code, which will require the
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relation module to be executed.'''
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if self.name in b_operators:
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return '%s.%s(%s)' % (self.left.toPython(),op_functions[self.name],self.right.toPython())
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elif self.name in u_operators:
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prop =self.prop
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#Converting parameters
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if self.name=='π':#Projection
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prop='\"%s\"' % prop.replace(' ','').replace(',','\",\"')
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elif self.name=="ρ": #Rename
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prop='{\"%s\"}' % prop.replace(',','\",\"').replace('➡','\":\"').replace(' ','')
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else: #Selection
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prop='\"%s\"' % prop
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return '%s.%s(%s)' % (self.child.toPython(),op_functions[self.name],prop)
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else:
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return self.name
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pass
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def result_format(self,rels):
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'''This function returns a list containing the fields that the resulting relation will have.
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Since it needs to know real instances of relations, it requires a dictionary where keys are
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the names of the relations and the values are the relation objects.'''
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if rels==None:
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return
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if self.kind==RELATION:
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return list(rels[self.name].header.attributes)
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elif self.kind==BINARY and self.name in ('-','ᑌ','ᑎ'):
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return self.left.result_format(rels)
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elif self.name=='π':
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l=[]
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for i in self.prop.split(','):
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l.append(i.strip())
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return l
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elif self.name=='*':
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return self.left.result_format(rels)+self.right.result_format(rels)
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elif self.name=='σ' :
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return self.child.result_format(rels)
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elif self.name=='ρ':
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_vars={}
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for i in self.prop.split(','):
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q=i.split('➡')
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_vars[q[0].strip()]=q[1].strip()
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_fields=self.child.result_format(rels)
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for i in range(len(_fields)):
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if _fields[i] in _vars:
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_fields[i]=_vars[_fields[i]]
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return _fields
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elif self.name in ('ᐅᐊ','ᐅLEFTᐊ','ᐅRIGHTᐊ','ᐅFULLᐊ'):
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return list(set(self.left.result_format(rels)).union(set(self.right.result_format(rels))))
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def __eq__(self,other):
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if not (isinstance(other,node) and self.name==other.name and self.kind==other.kind):
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return False
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if self.kind==UNARY:
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if other.prop!=self.prop:
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return False
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return self.child==other.child
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if self.kind==BINARY:
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return self.left==other.left and self.right==other.right
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return True
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def __str__(self):
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if (self.kind==RELATION):
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return self.name
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elif (self.kind==UNARY):
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return self.name + " "+ self.prop+ " (" + self.child.__str__() +")"
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elif (self.kind==BINARY):
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if self.left.kind==RELATION:
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le=self.left.__str__()
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else:
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le="("+self.left.__str__()+")"
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if self.right.kind==RELATION:
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re=self.right.__str__()
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else:
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re="("+self.right.__str__()+")"
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return (le+ self.name +re)
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def find_matching_parenthesis(expression,start=0):
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'''This function returns the position of the matching
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close parenthesis to the 1st open parenthesis found
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starting from start (0 by default)'''
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par_count=0 #Count of parenthesis
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for i in range(start,len(expression)):
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if expression[i]=='(':
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par_count+=1
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elif expression[i]==')':
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par_count-=1
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if par_count==0:
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return i #Closing parenthesis of the parameter
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def tokenize(expression):
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'''This function converts an expression into a list where
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every token of the expression is an item of a list. Expressions into
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parenthesis will be converted into sublists.'''
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items=[] #List for the tokens
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'''This is a state machine. Initial status is determined by the starting of the
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expression. There are the following statuses:
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relation: this is the status if the expressions begins with something else than an
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operator or a parenthesis.
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binary operator: this is the status when parsing a binary operator, nothing much to say
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unary operator: this status is more complex, since it will be followed by a parameter AND a
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sub-expression.
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sub-expression: this status is entered when finding a '(' and will be exited when finding a ')'.
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means that the others open must be counted to determine which close is the right one.'''
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expression=expression.strip() #Removes initial and endind spaces
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state=0
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'''
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0 initial and useless
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1 previous stuff was a relation
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2 previous stuff was a sub-expression
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3 previous stuff was a unary operator
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4 previous stuff was a binary operator
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'''
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while len(expression)>0:
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if expression.startswith('('): #Parenthesis state
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state=2
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end=find_matching_parenthesis(expression)
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#Appends the tokenization of the content of the parenthesis
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items.append(tokenize(expression[1:end]))
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#Removes the entire parentesis and content from the expression
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expression=expression[end+1:].strip()
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elif expression.startswith("σ") or expression.startswith("π") or expression.startswith("ρ"): #Unary 2 bytes
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items.append(expression[0:2]) #Adding operator in the top of the list
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expression=expression[2:].strip() #Removing operator from the expression
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if expression.startswith('('): #Expression with parenthesis, so adding what's between open and close without tokenization
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par=expression.find('(',find_matching_parenthesis(expression))
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else: #Expression without parenthesis, so adding what's between start and parenthesis as whole
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par=expression.find('(')
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items.append(expression[:par].strip()) #Inserting parameter of the operator
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expression=expression[par:].strip() #Removing parameter from the expression
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elif expression.startswith("*") or expression.startswith("-"): # Binary 1 byte
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items.append(expression[0])
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expression=expression[1:].strip() #1 char from the expression
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state=4
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elif expression.startswith("ᑎ") or expression.startswith("ᑌ"): #Binary short 3 bytes
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items.append(expression[0:3]) #Adding operator in the top of the list
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expression=expression[3:].strip() #Removing operator from the expression
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state=4
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elif expression.startswith("ᐅ"): #Binary long
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i=expression.find("ᐊ")
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items.append(expression[:i+3])
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expression=expression[i+3:].strip()
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state=4
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else: #Relation (hopefully)
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if state==1: #Previous was a relation, appending to the last token
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i=items.pop()
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items.append(i+expression[0])
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expression=expression[1:].strip() #1 char from the expression
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else:
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state=1
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items.append(expression[0])
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expression=expression[1:].strip() #1 char from the expression
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return items
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def tree(expression):
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'''This function parses a relational algebra expression into a tree and returns
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the root node using the Node class defined in this module.'''
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return node(tokenize(expression))
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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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It has 2 class of operators:
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without parameters
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*, -, ᑌ, ᑎ, ᐅᐊ, ᐅLEFTᐊ, ᐅRIGHTᐊ, ᐅFULLᐊ
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with parameters:
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σ, π, ρ
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Syntax for operators without parameters is:
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relation operator relation
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Syntax for operators with parameters is:
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operator parameters (relation)
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Since a*b is a relation itself, you can parse π a,b (a*b).
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And since π a,b (A) is a relation, you can parse π a,b (A) ᑌ B.
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You can use parenthesis to change priority: a ᐅᐊ (q ᑌ d).
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IMPORTANT: The encoding used by this module is UTF-8
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EXAMPLES
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σage > 25 and rank == weight(A)
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Q ᐅᐊ π a,b(A) ᐅᐊ B
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ρid➡i,name➡n(A) - π a,b(π a,b(A)) ᑎ σage > 25 or rank = weight(A)
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π a,b(π a,b(A))
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ρid➡i,name➡n(π a,b(A))
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A ᐅᐊ B
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'''
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return tree(expr).toPython()
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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) |