Re: [Pyparsing] How can I determine if a fragment is valid?

[Paul M. <pt...@au...>]

Here is the complete listing of the SQL expression parser I described in the
last message.

-- Paul


from pyparsing import *

sql1 = "select where foo = 1 and bar = 2 into result"
sql2 = "select where foo = 1 and bar = 2"

into_clause = Keyword('into') + restOfLine

selectStmt = Keyword('select') +
SkipTo(into_clause|StringEnd()).setResultsName('where_condition')

identifier = Word(alphas)
relationalOperator = oneOf("< = > >= <= != <>") 
integer = Word(nums) 
value = integer | sglQuotedString 
logicalComparison = identifier + relationalOperator + value

AND_cl = CaselessLiteral("AND")
OR_cl = CaselessLiteral("OR")
NOT_cl = CaselessLiteral("NOT")

complexComparison = operatorPrecedence( logicalComparison,
    [
    (NOT_cl, 1, opAssoc.RIGHT),
    (OR_cl, 2, opAssoc.LEFT),
    (AND_cl, 2, opAssoc.LEFT),
    ])

where_clause = CaselessLiteral("where") + complexComparison

selectStmt = Keyword('select') + where_clause('where_condition') + \
                Optional(into_clause)('into_clause')

print selectStmt.parseString(sql1).dump()
print selectStmt.parseString(sql2).dump()

Prints:
['select', 'where', [['foo', '=', '1'], 'AND', ['bar', '=', '2']], 'into', '
result']
- into_clause: ['into', ' result']
- where_condition: ['where', [['foo', '=', '1'], 'AND', ['bar', '=', '2']]]
['select', 'where', [['foo', '=', '1'], 'AND', ['bar', '=', '2']]]
- where_condition: ['where', [['foo', '=', '1'], 'AND', ['bar', '=', '2']]]