问题
I'm trying to use pyparsing to parse simple basic program:
import pyparsing as pp
pp.ParserElement.setDefaultWhitespaceChars(" \t")
EOL = pp.LineEnd().suppress()
# Identifiers is a string + optional $
identifier = pp.Combine(pp.Word(pp.alphas) + pp.Optional("$"))
# Literals (number or double quoted string)
literal = pp.pyparsing_common.number | pp.dblQuotedString
line_number = pp.pyparsing_common.integer
function = pp.Forward()
operand = function | identifier | literal
expression = pp.infixNotation(operand, [
(pp.oneOf("* / %"), 2, pp.opAssoc.LEFT),
(pp.oneOf("+ -"), 2, pp.opAssoc.LEFT),
])
assignment = identifier + "=" + expression
# Keywords
PRINT = pp.CaselessKeyword("print")
FOR = pp.CaselessKeyword("for")
TO = pp.CaselessKeyword("to")
STEP = pp.CaselessKeyword("step")
NEXT = pp.CaselessKeyword("next")
CHRS = pp.CaselessKeyword("chr$")
statement = pp.Forward()
print_stmt = PRINT + pp.ZeroOrMore(expression | ";")
for_stmt = FOR + assignment + TO + expression + pp.Optional(STEP + expression)
next_stmt = NEXT
chrs_fn = CHRS + "(" + expression + ")"
function <<= chrs_fn
statement <<= print_stmt | for_stmt | next_stmt | assignment
code_line = pp.Group(line_number + statement + EOL)
program = pp.ZeroOrMore(code_line)
test = """\
10 print 123;
20 print 234; 567;
25 next
30 print 890
"""
print(program.parseString(test).dump())
I do have everything else working except the print clause.
This is the output:
[[10, 'print', 123, ';', 20, 'print', 234, ';', 567, ';', 25, 'next', 30, 'print', 890]]
[0]:
[10, 'print', 123, ';', 20, 'print', 234, ';', 567, ';', 25, 'next', 30, 'print', 890]
Based on some suggetion I modified my parser but sitll for some reason parser leaks to next row.
How to define list of items for printing properly?
回答1:
There is a subtle thing going on here, and it bears better documenting when using ParserElement.setDefaultWhitespaceChars
. This only updates the whitespace characters for pyparsing expressions created after calling setDefaultWhitespaceChars
. The built-in expressions like dblQuotedString
and the expressions in pyparsing_common
are all defined at import time, and so get the standard set of whitespace characters to skip, which includes '\n'. If you create new copies of them using expr.copy()
or just plain expr()
, you will get new expressions, which use the updated whitespace characters.
Change:
literal = pp.pyparsing_common.number | pp.dblQuotedString
line_number = pp.pyparsing_common.integer
to:
literal = pp.pyparsing_common.number() | pp.dblQuotedString()
line_number = pp.pyparsing_common.integer()
And I think your leakage issues will be resolved.
来源:https://stackoverflow.com/questions/57744290/parse-a-list-of-expressions-using-pyparsing