Pyparsing可以很好地处理很小的语法，但是随着语法的增长，性能下降，内存使用率从高到低。
我当前的语法是：
newline = LineEnd ()
minus = Literal ('-')
plus = Literal ('+')
star = Literal ('*')
dash = Literal ('/')
dashdash = Literal ('//')
percent = Literal ('%')
starstar = Literal ('**')
lparen = Literal ('(')
rparen = Literal (')')
dot = Literal ('.')
comma = Literal (',')
eq = Literal ('=')
eqeq = Literal ('==')
lt = Literal ('<')
gt = Literal ('>')
le = Literal ('<=')
ge = Literal ('>=')
not_ = Keyword ('not')
and_ = Keyword ('and')
or_ = Keyword ('or')
ident = Word (alphas)
integer = Word (nums)
expr = Forward ()
parenthized = Group (lparen + expr + rparen)
trailer = (dot + ident)
atom = ident | integer | parenthized
factor = Forward ()
power = atom + ZeroOrMore (trailer) + Optional (starstar + factor)
factor << (ZeroOrMore (minus | plus) + power)
term = ZeroOrMore (factor + (star | dashdash | dash | percent) ) + factor
arith = ZeroOrMore (term + (minus | plus) ) + term
comp = ZeroOrMore (arith + (eqeq | le | ge | lt | gt) ) + arith
boolNot = ZeroOrMore (not_) + comp
boolAnd = ZeroOrMore (boolNot + and_) + boolNot
boolOr = ZeroOrMore (boolAnd + or_) + boolAnd
match = ZeroOrMore (ident + eq) + boolOr
expr << match
statement = expr + newline
program = OneOrMore (statement)
当我解析以下内容
print (program.parseString ('3*(1+2*3*(4+5))\n') )
这需要很长时间：
~/Desktop/m2/pyp$ time python3 slow.py
['3', '*', ['(', '1', '+', '2', '*', '3', '*', ['(', '4', '+', '5', ')'], ')']]
real 0m27.280s
user 0m25.844s
sys 0m1.364s
并且内存使用率上升到1.7 GiB（sic！）。
我在实施此语法时是否犯了一些严重的错误，或者我该如何使内存使用率保持在可接受的范围内？
导入pyparsing后，启用packrat解析以记录解析行为：
ParserElement.enablePackrat()
这将大大提高性能。
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