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PyScript demo of a pyparsing arithmetic parser/evaluator
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| <html> | |
| <head> | |
| <script defer src="https://pyscript.net/alpha/pyscript.js"></script> | |
| </head> | |
| <body> | |
| <table cellpadding=30 border=2> | |
| <tr> | |
| <td> | |
| <pre> | |
| # Parse an arithmetic expression into elements according | |
| # to standard operator precedence rules. | |
| import pyparsing as pp | |
| integer = pp.common.integer | |
| arith_expr = pp.infix_notation(integer, | |
| [ | |
| ('-', 1, pp.OpAssoc.RIGHT), | |
| (pp.one_of('* /'), 2, pp.OpAssoc.LEFT), | |
| (pp.one_of('+ -'), 2, pp.OpAssoc.LEFT), | |
| ]) | |
| # try it out! | |
| arith = "10*3+4/2" | |
| print(arith_expr.parse_string(arith).as_list()) | |
| ============================ | |
| <py-script> | |
| import pyparsing as pp | |
| integer = pp.common.integer | |
| arith_expr = pp.infix_notation(integer, | |
| [ | |
| ('-', 1, pp.OpAssoc.RIGHT), | |
| (pp.one_of('* /'), 2, pp.OpAssoc.LEFT), | |
| (pp.one_of('+ -'), 2, pp.OpAssoc.LEFT), | |
| ]) | |
| # try it out! | |
| arith = "10*3+4/2" | |
| print(arith_expr.parse_string(arith).as_list()) | |
| </py-script> | |
| </pre> | |
| </td> | |
| </tr> | |
| <tr> | |
| <td> | |
| <pre> | |
| # Parse and evaluate an arithmetic expression according | |
| # to standard operator precedence rules. | |
| import operator | |
| import pyparsing as pp | |
| integer = pp.common.integer | |
| # add parse actions to evaluate the arithmetic expression | |
| def eval_unary_minus(t): | |
| t, = t | |
| return -(t[1]) | |
| def eval_binary(t): | |
| op_map = { | |
| '+': operator.add, | |
| '-': operator.sub, | |
| '*': operator.mul, | |
| '/': operator.truediv, | |
| } | |
| t, = t | |
| ret = t[0] | |
| for op, operand in zip(t[1::2], t[2::2]): | |
| ret = op_map[op](ret, operand) | |
| return ret | |
| eval_expr = pp.infix_notation(integer, | |
| [ | |
| ('-', 1, pp.OpAssoc.RIGHT, eval_unary_minus), | |
| (pp.one_of('* /'), 2, pp.OpAssoc.LEFT, eval_binary), | |
| (pp.one_of('+ -'), 2, pp.OpAssoc.LEFT, eval_binary), | |
| ]) | |
| # try it out! | |
| arith = "10*3+4/2" | |
| print(eval_expr.parse_string(arith)[0]) | |
| ============================ | |
| <py-script> | |
| import operator | |
| # add parse actions to evaluate the arithmetic expression | |
| def eval_unary_minus(t): | |
| t, = t | |
| return -(t[1]) | |
| def eval_binary(t): | |
| op_map = { | |
| '+': operator.add, | |
| '-': operator.sub, | |
| '*': operator.mul, | |
| '/': operator.truediv, | |
| } | |
| t, = t | |
| ret = t[0] | |
| for op, operand in zip(t[1::2], t[2::2]): | |
| ret = op_map[op](ret, operand) | |
| return ret | |
| eval_expr = pp.infix_notation(integer, | |
| [ | |
| ('-', 1, pp.OpAssoc.RIGHT, eval_unary_minus), | |
| (pp.one_of('* /'), 2, pp.OpAssoc.LEFT, eval_binary), | |
| (pp.one_of('+ -'), 2, pp.OpAssoc.LEFT, eval_binary), | |
| ]) | |
| # try it out! | |
| arith = "10*3+4/2" | |
| print(eval_expr.parse_string(arith)[0]) | |
| </py-script> | |
| </pre> | |
| </td> | |
| </tr> | |
| </table> | |
| </body> | |
| </html> |
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