parser for formula using python

Question

I want to construct a parse tree of bracketed formula using python.

For example,

parse tree of ((x='a' OR x= 'b') AND(y ='c' OR y = 'd' )) using python

The formula not necessarily is in normal form. It could be a k-depth circuit as well.

The parser also should allow '>=', '<=', '!=' etc operators.

Which of the parser available will be most effective/efficient for my purpose?

What do you want to do with the parsed result? Simple execution of the code is I guess not the solution.. — Dr. Jan-Philip Gehrcke, May 24 '14 at 20:49
@Jan-Philip Gehrcke: I want the tree only. Trying to implement some database searching mechanism. — mxant, May 24 '14 at 20:52

score 1 · Answer 1 · answered May 24 '14 at 21:58

I'm a "cheat early, cheat often" kind of guy. The following translates your input code into a Python expression, parses it using the normal mechanism, then prints out the structure.

import ast, re

source = "((x='a' OR x= 'b') AND(y ='c' OR y = 'd' ))"

# turn source '=' into Python '==', unless it's part of a compound
# IE: <= >= != => =< =!
py_source = re.compile(
    r'(?<=  [^<>!]  )'
    r'='
    r'(?<=  [^<>!]  )',
    re.VERBOSE).sub('==', source.lower())

print 'SOURCE:', source
print 'PYTHON:', py_source

print ast.dump( ast.parse(py_source) )

Example output:

SOURCE: ((x='a' OR x= 'b') AND(y ='c' OR y = 'd' ))
PYTHON: ((x=='a' or x== 'b') and(y =='c' or y == 'd' ))

Module(body=[Expr(value=BoolOp(op=And(), values=[BoolOp(op=Or(), values=[Compare(left=Name(id='x', ctx=Load()), ops=[Eq()], comparators=[Str(s='a')]), Compare(left=Name(id='x', ctx=Load()), ops=[Eq()], comparators=[Str(s='b')])]), BoolOp(op=Or(), values=[Compare(left=Name(id='y', ctx=Load()), ops=[Eq()], comparators=[Str(s='c')]), Compare(left=Name(id='y', ctx=Load()), ops=[Eq()], comparators=[Str(s='d')])])]))])

Thanks for the code. Although I wanted some package name only that has this kind of capability in a simple way - (Which of the parser available will be most effective/efficient for my purpose?). Thanks again for the effort. — mxant, May 25 '14 at 14:38

parser for formula using python

1 Answers1