How to define function from input string in python at runtime?

Question

I was trying to solve UVA 11036. It requires defining function at runtime.

For Example: I have to take input (2*x + 7) % N as a string and define a function at runtime like func = lambda x : (2*x + 7) % N to work on it. Please help me to find out how to convert string to function at runtime.

That problem doesn't require defining a function from a string. You should parse the RPN and generate a function dynamically using functional composition. — Barmar, Aug 20 '20 at 06:33

Ahad Rafat Talebi · Answer 1 · 2020-08-20T07:49:09.060

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It seems captivating riddle, so if you want to solve it in C++ have two way. The hard way is implementing a small math parser using some algorithms like Shunting-yard algorithm. Or instead of, if you are familiar with library linking in C++, it is better to use a mathematical expression parser libraries. There are many libraries on Internet. Here, I suggest one of them as below.

mathematical expression library I personalty have tested it and obviously is fast. you can clone source code in GitHub

Anyway, you can not solve this case with lambda functions because, the input is a mathematical expression you should parse and calculate it runtime.

if you use python see this post.

edited Aug 20 '20 at 07:49

answered Aug 20 '20 at 07:38

Ahad Rafat Talebi

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did you mean http://www.partow.net/programming/exprtk/index.html – rioV8 Aug 20 '20 at 07:57
@rioV8 Yes it is that. – Ahad Rafat Talebi Aug 20 '20 at 08:29

score 1 · Accepted Answer · answered Aug 20 '20 at 07:50

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You could use exec to define a function from a string. However that allows to inject any code into your program. But as it's only for solving that challenge, it might be fine.

exec 'func = lambda x : '+input

answered Aug 20 '20 at 07:50

Finn

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How to define function from input string in python at runtime?

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