Re: [Pyparsing] How to distinguish a variable from a integer

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

> I said that an operand could be a variable or a number to simplify things
> given that the problem was between numbers and variables. But it's
> actually
> more complex than that: It could be a quoted string or a set (in the form
> "{element1, element2, ...}" where each element can be a number, variable,
> quoted string or even another set) too:
> 
> operand = number | string | variable | set
> 
Ah, with that said, let me then suggest this as a starting point for
implementing operand (assuming that variables can *not* start with a digit):

LBRACE = Suppress('{')
RBRACE = Suppress('}')
operand = Forward()
number = #...(as you have defined it in your original code)
string_ = quotedString.setParseAction(removeQuotes)
variable = #...(use your Unicode definition of choice)
set_ = Group(LBRACE + delimitedList(operand) + RBRACE)
operand << (number | string_ | variable | set_)

delimitedList takes care of the repetition with intervening comma delimited.
Group packages the result in its own list, so that recursive set definitions
will maintain their nesting properly.  The set-enclosing braces are
suppressed from the output - they are useful during parsing, but unnecessary
once the tokens have been grouped.

This is the canonical form for defining a recursive expression like your
operand, mas o menos.  Now you are free to include operand in other
expressions, or even operatorPrecedence.
    
-- Paul