"MooMaster" <[EMAIL PROTECTED]> wrote in message
news:[EMAIL PROTECTED]
> I'm trying to develop a little script that does some string
> manipulation. I have some few hundred strings that currently look like
> this:
>
> cond(a,b,c)
>
> and I want them to look like this:
>
> cond(c,a,b)
<snip>
Pyparsing makes this a fairly tractable problem. The hardest part is
defining the valid contents of a relational and arithmetic expression, which
may be found within the arguments of your cond(a,b,c) constructs.
Not guaranteeing this 100%, but it did convert your pathologically nested
example on the first try.
-- Paul
----------
from pyparsing import *
ident = ~Literal("cond") + Word(alphas)
number = Combine(Optional("-") + Word(nums) + Optional("." + Word(nums)))
arithExpr = Forward()
funcCall = ident+"("+delimitedList(arithExpr)+")"
operand = number | funcCall | ident
binop = oneOf("+ - * /")
arithExpr << ( ( operand + ZeroOrMore( binop + operand ) ) | ("(" +
arithExpr + ")" ) )
relop = oneOf("< > == <= >= != <>")
condDef = Forward()
simpleCondExpr = arithExpr + ZeroOrMore( relop + arithExpr ) | condDef
multCondExpr = simpleCondExpr + "*" + arithExpr
condExpr = Forward()
condExpr << ( simpleCondExpr | multCondExpr | "(" + condExpr + ")" )
def reorderArgs(t):
return "cond(" + ",".join(["".join(t.arg3), "".join(t.arg1),
"".join(t.arg2)]) + ")"
condDef << ( Literal("cond") + "(" + Group(condExpr).setResultsName("arg1")
+ "," +
Group(condExpr).setResultsName("arg2")
+ "," +
Group(condExpr).setResultsName("arg3")
+ ")" ).setParseAction( reorderArgs )
tests = [
"cond(a,b,c)",
"cond(1>2,b,c)",
"cond(-1,1,f)*((float(e)*(2**4))+(float(d)*8)+(float(c)*4)+(float(b)*2)+floa
t(a))",
"cond(a,b,(abs(c) >= d))",
"cond(0,cond(c,cond(e,cond(g,h,(a<f)),(a<d)),(a<b)),(a<1))",
]
for t in tests:
print t,"->",condExpr.transformString(t)
----------
Prints:
cond(a,b,c) -> cond(c,a,b)
cond(1>2,b,c) -> cond(c,1>2,b)
cond(-1,1,f)*((float(e)*(2**4))+(float(d)*8)+(float(c)*4)+(float(b)*2)+float
(a)) ->
cond(f,-1,1)*((float(e)*(2**4))+(float(d)*8)+(float(c)*4)+(float(b)*2)+float
(a))
cond(a,b,(abs(c) >= d)) -> cond((abs(c)>=d),a,b)
cond(0,cond(c,cond(e,cond(g,h,(a<f)),(a<d)),(a<b)),(a<1)) ->
cond((a<1),0,cond((a<b),c,cond((a<d),e,cond((a<f),g,h))))
--
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