parser completed
git-svn-id: http://galileo.dmi.unict.it/svn/relational/trunk@18 014f5005-505e-4b48-8d0a-63407b615a7c
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LtWorf
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parser.py
138
parser.py
@ -18,81 +18,103 @@
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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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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, ᐅᐊLEFT, ᐅᐊRIGHT, ᐅᐊFULL
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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't use parenthesis to change priority: a ᐅᐊ (q ᑌ d)
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must be written as q ᑌ d ᐅᐊ a
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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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symbols=("σ","π","ρ")
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expr=expr.strip()
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print "====PARSING: ",expr
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start=-1
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end=-1
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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 from end to begin
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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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start=i+1
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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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end=i
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break
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if start==-1: #No complex operators
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return parse_op(expr)
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else:
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#internal=expr[0:start]+ parse(expr[start:end])+expr[end:]
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internal=parse(expr[start:end])
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print "EXPRESSION: %s" % (internal)
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endp=start-1
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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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parameters=expr[start:endp]
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print "===Internal: %s\t Parameters: %s" %(internal,parameters)
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res=""
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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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starts.append(i)
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res="%s.projection(%s)" % (internal,params)
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elif symbol== "σ": #Selection
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res="%s.selection(\"%s\")" % (internal,parameters)
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elif symbol=="ρ": #Rename
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params=parameters.replace(",","\",\"").replace("➡","\",\"")
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res="%s.rename(\"%s\")" % (internal,params)
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print res
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res= ("%s%s%s") % (expr[0:start-2],res.replace(" ",""),expr[end+1:])
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return parse_op(res)
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#Selection σage > 25 Λ rank = weight(A)
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#Projection Q ᐅᐊ π a,b(A) ᐅᐊ B
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#Rename ρid➡i,name➡n(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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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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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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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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elif symbol== "σ": #Selection
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res="%s.selection(\"%s\")" % (internal,parameters)
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elif symbol=="ρ": #Rename
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params=parameters.replace(",","\",\"").replace("➡","\",\"")
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res="%s.rename(\"%s\")" % (internal,params)
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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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expr= ("%s%s%s") % (expr[0:start-2],res,expr[end+1:])
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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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(not functions) and no parenthesis, converting it into python,
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executable by eval function to get the result of the expression.'''
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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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