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How can I allow users to execute mathematical expressions in a safe way? Do I need to write a full parser?
Is there something like ast.literal_eval(), but for expressions?
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Making experiments. As the generated C parser is the one used by Python, this means that if something goes wrong when adding some new rules to the grammar you cannot correctly compile and execute Python anymore.
Python parsing is done using various ways such as the use of parser module, parsing using regular expressions, parsing using some string methods such as split() and strip(), parsing using pandas such as reading CSV file to text by using read. csv, etc.
The Pyparsing examples page lists several expression parsers:
http://pyparsing.wikispaces.com/file/view/fourFn.py - A conventional arithmetic infix notation parser/evaluator implementation using pyparsing (despite its name, this actually does 5-function arithmetic, plus several trig functions)
http://pyparsing.wikispaces.com/file/view/simpleBool.py - A boolean infix notation parser/evaluator, using a pyparsing helper method operatorPrecedence, which simplifies the definition of infix operator notations
http://pyparsing.wikispaces.com/file/view/simpleArith.py http://pyparsing.wikispaces.com/file/view/eval_arith.py -
A pair of examples recasting fourFn.py using operatorPrecedence. The first just parses and returns a parse tree, the second adds evaluation logic.
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