How safe is expression evaluation using eval?

Question

I am building a website where I have a need that user should be able to evaluate some expression based from the value in DB tables, instead of using tools like pyparsing etc

Answer 1

It is possible to get create and invoke any class defined in the program, which includes ones that can exit the Python interpreter. In addition, you can create and execute arbitrary strings of bytecode, which can segfault the interpreter. See Eval really is dangerous for all the details.