377 lines
14 KiB
Python
377 lines
14 KiB
Python
# Relational
|
||
# Copyright (C) 2008-2016 Salvo "LtWorf" Tomaselli
|
||
#
|
||
# Relational is free software: you can redistribute it and/or modify
|
||
# it under the terms of the GNU General Public License as published by
|
||
# the Free Software Foundation, either version 3 of the License, or
|
||
# (at your option) any later version.
|
||
#
|
||
# This program is distributed in the hope that it will be useful,
|
||
# but WITHOUT ANY WARRANTY; without even the implied warranty of
|
||
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
|
||
# GNU General Public License for more details.
|
||
#
|
||
# You should have received a copy of the GNU General Public License
|
||
# along with this program. If not, see <http://www.gnu.org/licenses/>.
|
||
#
|
||
# author Salvo "LtWorf" Tomaselli <tiposchi@tiscali.it>
|
||
#
|
||
#
|
||
#
|
||
# This module implements a parser for relational algebra, and can be used
|
||
# to convert expressions into python expressions and to get the parse-tree
|
||
# of the expression.
|
||
#
|
||
# Language definition here:
|
||
# http://ltworf.github.io/relational/grammar.html
|
||
from relational import rtypes
|
||
|
||
RELATION = 0
|
||
UNARY = 1
|
||
BINARY = 2
|
||
|
||
PRODUCT = '*'
|
||
DIFFERENCE = '-'
|
||
UNION = '∪'
|
||
INTERSECTION = '∩'
|
||
DIVISION = '÷'
|
||
JOIN = '⋈'
|
||
JOIN_LEFT = '⧑'
|
||
JOIN_RIGHT = '⧒'
|
||
JOIN_FULL = '⧓'
|
||
PROJECTION = 'π'
|
||
SELECTION = 'σ'
|
||
RENAME = 'ρ'
|
||
ARROW = '➡'
|
||
|
||
b_operators = (PRODUCT, DIFFERENCE, UNION, INTERSECTION, DIVISION,
|
||
JOIN, JOIN_LEFT, JOIN_RIGHT, JOIN_FULL) # List of binary operators
|
||
u_operators = (PROJECTION, SELECTION, RENAME) # List of unary operators
|
||
|
||
# Associates operator with python method
|
||
op_functions = {
|
||
PRODUCT: 'product', DIFFERENCE: 'difference', UNION: 'union', INTERSECTION: 'intersection', DIVISION: 'division', JOIN: 'join',
|
||
JOIN_LEFT: 'outer_left', JOIN_RIGHT: 'outer_right', JOIN_FULL: 'outer', PROJECTION: 'projection', SELECTION: 'selection', RENAME: 'rename'}
|
||
|
||
|
||
class TokenizerException (Exception):
|
||
pass
|
||
|
||
|
||
class ParserException (Exception):
|
||
pass
|
||
|
||
|
||
class CallableString(str):
|
||
|
||
'''
|
||
This is a string. However it is also callable.
|
||
|
||
For example:
|
||
CallableString('1+1')()
|
||
returns 2
|
||
|
||
It is used to contain Python expressions and print
|
||
or execute them.
|
||
'''
|
||
|
||
def __call__(self, context=None):
|
||
'''
|
||
context is a dictionary where to
|
||
each name is associated the relative relation
|
||
'''
|
||
return eval(self, context)
|
||
|
||
|
||
class Node (object):
|
||
|
||
'''This class is a node of a relational expression. Leaves are relations
|
||
and internal nodes are operations.
|
||
|
||
The 'kind' property indicates whether the node is a binary operator, unary
|
||
operator or relation.
|
||
Since relations are leaves, a relation node will have no attribute for
|
||
children.
|
||
|
||
If the node is a binary operator, it will have left and right properties.
|
||
|
||
If the node is a unary operator, it will have a child, pointing to the
|
||
child node and a property containing the string with the props of the
|
||
operation.
|
||
|
||
This class is used to convert an expression into python code.'''
|
||
kind = None
|
||
__hash__ = None
|
||
|
||
def __init__(self, expression=None):
|
||
'''Generates the tree from the tokenized expression
|
||
If no expression is specified then it will create an empty node'''
|
||
if expression == None or len(expression) == 0:
|
||
return
|
||
|
||
# If the list contains only a list, it will consider the lower level list.
|
||
# This will allow things like ((((((a))))) to work
|
||
while len(expression) == 1 and isinstance(expression[0], list):
|
||
expression = expression[0]
|
||
|
||
# The list contains only 1 string. Means it is the name of a relation
|
||
if len(expression) == 1:
|
||
self.kind = RELATION
|
||
self.name = expression[0]
|
||
if not rtypes.is_valid_relation_name(self.name):
|
||
raise ParserException(
|
||
u"'%s' is not a valid relation name" % self.name)
|
||
return
|
||
|
||
# Expression from right to left, searching for binary operators
|
||
# this means that binary operators have lesser priority than
|
||
# unary operators.
|
||
# It finds the operator with lesser priority, uses it as root of this
|
||
# (sub)tree using everything on its left as left parameter (so building
|
||
# a left subtree with the part of the list located on left) and doing
|
||
# the same on right.
|
||
# Since it searches for strings, and expressions into parenthesis are
|
||
# within sub-lists, they won't be found here, ensuring that they will
|
||
# have highest priority.
|
||
for i in range(len(expression) - 1, -1, -1):
|
||
if expression[i] in b_operators: # Binary operator
|
||
self.kind = BINARY
|
||
self.name = expression[i]
|
||
|
||
if len(expression[:i]) == 0:
|
||
raise ParserException(
|
||
u"Expected left operand for '%s'" % self.name)
|
||
|
||
if len(expression[i + 1:]) == 0:
|
||
raise ParserException(
|
||
u"Expected right operand for '%s'" % self.name)
|
||
|
||
self.left = node(expression[:i])
|
||
self.right = node(expression[i + 1:])
|
||
return
|
||
'''Searches for unary operators, parsing from right to left'''
|
||
for i in range(len(expression) - 1, -1, -1):
|
||
if expression[i] in u_operators: # Unary operator
|
||
self.kind = UNARY
|
||
self.name = expression[i]
|
||
|
||
if len(expression) <= i + 2:
|
||
raise ParserException(
|
||
u"Expected more tokens in '%s'" % self.name)
|
||
|
||
self.prop = expression[1 + i].strip()
|
||
self.child = node(expression[2 + i])
|
||
|
||
return
|
||
raise ParserException("Expected operator in '%s'" % expression)
|
||
|
||
def toCode(self):
|
||
'''This method converts the AST into a python code object'''
|
||
code = self._toPython()
|
||
return compile(code, '<relational_expression>', 'eval')
|
||
|
||
def toPython(self):
|
||
'''This method converts the AST into a python code string, which
|
||
will require the relation module to be executed.
|
||
|
||
The return value is a CallableString, which means that it can be
|
||
directly called.'''
|
||
return CallableString(self._toPython())
|
||
|
||
def _toPython(self):
|
||
'''
|
||
Same as toPython but returns a regular string
|
||
'''
|
||
if self.name in b_operators:
|
||
return '%s.%s(%s)' % (self.left.toPython(), op_functions[self.name], self.right.toPython())
|
||
elif self.name in u_operators:
|
||
prop = self.prop
|
||
|
||
# Converting parameters
|
||
if self.name == PROJECTION:
|
||
prop = '\"%s\"' % prop.replace(' ', '').replace(',', '\",\"')
|
||
elif self.name == RENAME:
|
||
prop = '{\"%s\"}' % prop.replace(
|
||
',', '\",\"').replace(ARROW, '\":\"').replace(' ', '')
|
||
else: # Selection
|
||
prop = '\"%s\"' % prop
|
||
|
||
return '%s.%s(%s)' % (self.child.toPython(), op_functions[self.name], prop)
|
||
return self.name
|
||
|
||
def printtree(self, level=0):
|
||
'''returns a representation of the tree using indentation'''
|
||
r = ''
|
||
for i in range(level):
|
||
r += ' '
|
||
r += self.name
|
||
if self.name in b_operators:
|
||
r += self.left.printtree(level + 1)
|
||
r += self.right.printtree(level + 1)
|
||
elif self.name in u_operators:
|
||
r += '\t%s\n' % self.prop
|
||
r += self.child.printtree(level + 1)
|
||
|
||
return '\n' + r
|
||
|
||
def get_left_leaf(self):
|
||
'''This function returns the leftmost leaf in the tree.'''
|
||
if self.kind == RELATION:
|
||
return self
|
||
elif self.kind == UNARY:
|
||
return self.child.get_left_leaf()
|
||
elif self.kind == BINARY:
|
||
return self.left.get_left_leaf()
|
||
|
||
def result_format(self, rels):
|
||
'''This function returns a list containing the fields that the resulting relation will have.
|
||
It requires a dictionary where keys are the names of the relations and the values are
|
||
the relation objects.'''
|
||
if rels == None:
|
||
return
|
||
|
||
if self.kind == RELATION:
|
||
return list(rels[self.name].header)
|
||
elif self.kind == BINARY and self.name in (DIFFERENCE, UNION, INTERSECTION):
|
||
return self.left.result_format(rels)
|
||
elif self.kind == BINARY and self.name == DIVISION:
|
||
return list(set(self.left.result_format(rels)) - set(self.right.result_format(rels)))
|
||
elif self.name == PROJECTION:
|
||
l = []
|
||
for i in self.prop.split(','):
|
||
l.append(i.strip())
|
||
return l
|
||
elif self.name == PRODUCT:
|
||
return self.left.result_format(rels) + self.right.result_format(rels)
|
||
elif self.name == SELECTION:
|
||
return self.child.result_format(rels)
|
||
elif self.name == RENAME:
|
||
_vars = {}
|
||
for i in self.prop.split(','):
|
||
q = i.split(ARROW)
|
||
_vars[q[0].strip()] = q[1].strip()
|
||
|
||
_fields = self.child.result_format(rels)
|
||
for i in range(len(_fields)):
|
||
if _fields[i] in _vars:
|
||
_fields[i] = _vars[_fields[i]]
|
||
return _fields
|
||
elif self.name in (JOIN, JOIN_LEFT, JOIN_RIGHT, JOIN_FULL):
|
||
return list(set(self.left.result_format(rels)).union(set(self.right.result_format(rels))))
|
||
|
||
def __eq__(self, other):
|
||
if not (isinstance(other, node) and self.name == other.name and self.kind == other.kind):
|
||
return False
|
||
|
||
if self.kind == UNARY:
|
||
if other.prop != self.prop:
|
||
return False
|
||
return self.child == other.child
|
||
if self.kind == BINARY:
|
||
return self.left == other.left and self.right == other.right
|
||
return True
|
||
|
||
def __str__(self):
|
||
if (self.kind == RELATION):
|
||
return self.name
|
||
elif (self.kind == UNARY):
|
||
return self.name + " " + self.prop + " (" + self.child.__str__() + ")"
|
||
elif (self.kind == BINARY):
|
||
if self.left.kind == RELATION:
|
||
le = self.left.__str__()
|
||
else:
|
||
le = "(" + self.left.__str__() + ")"
|
||
if self.right.kind == RELATION:
|
||
re = self.right.__str__()
|
||
else:
|
||
re = "(" + self.right.__str__() + ")"
|
||
|
||
return (le + self.name + re)
|
||
|
||
|
||
def _find_matching_parenthesis(expression, start=0, openpar=u'(', closepar=u')'):
|
||
'''This function returns the position of the matching
|
||
close parenthesis to the 1st open parenthesis found
|
||
starting from start (0 by default)'''
|
||
par_count = 0 # Count of parenthesis
|
||
for i in range(start, len(expression)):
|
||
if expression[i] == openpar:
|
||
par_count += 1
|
||
elif expression[i] == closepar:
|
||
par_count -= 1
|
||
if par_count == 0:
|
||
return i # Closing parenthesis of the parameter
|
||
|
||
|
||
def tokenize(expression):
|
||
'''This function converts a relational expression into a list where
|
||
every token of the expression is an item of a list. Expressions into
|
||
parenthesis will be converted into sublists.'''
|
||
|
||
items = [] # List for the tokens
|
||
|
||
expression = expression.strip() # Removes initial and ending spaces
|
||
|
||
while len(expression) > 0:
|
||
|
||
if expression.startswith('('): # Parenthesis state
|
||
end = _find_matching_parenthesis(expression)
|
||
if end == None:
|
||
raise TokenizerException(
|
||
"Missing matching ')' in '%s'" % expression)
|
||
# Appends the tokenization of the content of the parenthesis
|
||
items.append(tokenize(expression[1:end]))
|
||
# Removes the entire parentesis and content from the expression
|
||
expression = expression[end + 1:].strip()
|
||
|
||
elif expression.startswith((SELECTION, RENAME, PROJECTION)): # Unary operators
|
||
items.append(expression[0:1])
|
||
# Adding operator in the top of the list
|
||
expression = expression[
|
||
1:].strip() # Removing operator from the expression
|
||
|
||
if expression.startswith('('): # Expression with parenthesis, so adding what's between open and close without tokenization
|
||
par = expression.find(
|
||
'(', _find_matching_parenthesis(expression))
|
||
else: # Expression without parenthesis, so adding what's between start and parenthesis as whole
|
||
par = expression.find('(')
|
||
|
||
items.append(expression[:par].strip())
|
||
# Inserting parameter of the operator
|
||
expression = expression[
|
||
par:].strip() # Removing parameter from the expression
|
||
else: # Relation (hopefully)
|
||
expression += ' ' # To avoid the special case of the ending
|
||
|
||
# Initial part is a relation, stop when the name of the relation is
|
||
# over
|
||
for r in range(1, len(expression)):
|
||
if rtypes.RELATION_NAME_REGEXP.match(expression[:r + 1]) is None:
|
||
break
|
||
items.append(expression[:r])
|
||
expression = expression[r:].strip()
|
||
|
||
return items
|
||
|
||
|
||
def tree(expression):
|
||
'''This function parses a relational algebra expression into a AST and returns
|
||
the root node using the Node class.'''
|
||
return node(tokenize(expression))
|
||
|
||
|
||
def parse(expr):
|
||
'''This function parses a relational algebra expression, and returns a
|
||
CallableString (a string that can be called) whith the corresponding
|
||
Python expression.
|
||
'''
|
||
return tree(expr).toPython()
|
||
|
||
if __name__ == "__main__":
|
||
while True:
|
||
e = input("Expression: ")
|
||
print (parse(e))
|
||
|
||
# Backwards compatibility
|
||
node = Node
|