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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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