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@ -1,3 +1,4 @@
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# -*- 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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@ -16,6 +17,9 @@
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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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import optimizer
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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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@ -46,120 +50,8 @@ def parse(expr):
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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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symbols=("σ","π","ρ")
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return optimizer.tree(expr).toPython()
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starts=[]#List with starts and ends
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parenthesis=0
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lexpr=list(expr)
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#Parses the string finding all 1st level parenthesis
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for i in range(len(lexpr)):
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if lexpr[i]=="(":
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if parenthesis==0:
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starts.append(i+1)
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parenthesis+=1
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elif lexpr[i]==")":
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parenthesis-=1
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if parenthesis==0:
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starts.append(i)
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if len(starts)==0: #No parenthesis: no operators with parameters
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return parse_op(expr)
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while len(starts)>0:
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#Converting the last complex operator into python
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end=starts.pop()
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start=starts.pop()
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internal=parse(expr[start:end])
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endp=start-1
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symbol=""
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for i in range(endp,-1,-1):
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if expr[i:i+2] in symbols:
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symbol=expr[i:i+2]
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start=i+2
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break
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if expr[i:i+1] ==")":
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break #No symbol before
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parameters=expr[start:endp]
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res="" #String for result
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if symbol=="π":#Projection
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params=""
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count=0
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for i in parameters.split(","):
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if count!=0:
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params+=","
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else:
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count=1
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params+="\"%s\"" % (i.strip())
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res="%s.projection(%s)" % (internal,params)
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expr= ("%s%s%s") % (expr[0:start-2],res,expr[end+1:])
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elif symbol== "σ": #Selection
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res="%s.selection(\"%s\")" % (internal,parameters)
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expr= ("%s%s%s") % (expr[0:start-2],res,expr[end+1:])
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elif symbol=="ρ": #Rename
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params=parameters.replace(",","\",\"").replace("➡","\":\"").replace(" ","")
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res="%s.rename({\"%s\"})" % (internal,params)
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expr= ("%s%s%s") % (expr[0:start-2],res,expr[end+1:])
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else:
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res="(%s)" % (internal)
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expr= ("%s%s%s") % (expr[0:start-1],res,expr[end+1:])
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#Last complex operator is replaced with it's python code
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#Next cycle will do the same to the new last unparsed complex operator
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#At the end, parse_op will convert operators without parameters
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return parse_op(expr)
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def parse_op(expr):
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'''This function parses a relational algebra expression including only operators
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without parameters, converting it into python.
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Executable by eval function to get the result of the expression.'''
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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["ᐅLEFTᐊ"]=".outer_left(%s)"
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symbols["ᐅRIGHTᐊ"]=".outer_right(%s)"
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symbols["ᐅFULLᐊ"]=".outer(%s)"
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symbols["ᐅᐊ"]=".join(%s)"
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#We want to avoid to parse expressions within quotes.
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#We split the string into an array, and we parse only the ones with even index
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quotes=expr.split('"');
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for i in range (0,len(quotes),2):
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for j in symbols:
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quotes[i]=quotes[i].replace(j,"_____%s_____"% (j))
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#The parts outside the quotes was parsed, put the string together again
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if (len(quotes)>1):
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expr= '"'.join(quotes)
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else:
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expr= quotes[0]
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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].strip()
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else:
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result+=symbols[tokens[i]] % (tokens[i+1].strip())
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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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LtWorf