Python how to call a class method from a string that contains parameters

Question

I have the following code. What would be the best way to evaluate the command variable and the parameters it contains.

This is a contrived example, but the easiest way to explain what I am trying to do on a bigger scale.

class Job():
  def random_number(self, start, end, prec=0):
    number = round(random.uniform(start,end),prec)
    if(prec == 0):
      return int(number)
    return number

  def run(self, command):
    #command = "self.random_number(1,10,0)"
    #**************
    # What would be the best way to 'eval' the content of the 'command' variable and the parameters it contains?
    #**************

job = Job()
job.run("self.random_number(1,10,0)")

Jan · Accepted Answer · 2020-07-12 11:01:41Z

5

Generally, this seems a bad idea, consider restructuring your code. That said, you may make use of getattr(...) in combination with splitting your string into a function and a params part:

import random, re

class Job():
    def random_number(self, start, end, prec=0):
        number = round(random.uniform(start, end), prec)
        if (prec == 0):
            return int(number)
        return number

    def run(self, command):
        fun, params, _ = re.split(r'[()]', command)
        params = map(int, params.split(","))

        func = getattr(Job, fun)
        print(func(*params))

job = Job()
job.run("random_number(1,10,0)")

Obviously, you'd need to add some error management (broken strings, functions, that don't exist, floats instead of integers - you get the idea).

edited Jul 12, 2020 at 11:01

answered Jul 12, 2020 at 10:53

Jan

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1 Comment

PrestonDocks Over a year ago

Thank you, it was that regex that I was looking for. That will help me out a lot, and I am actively working on redesigning the code, but I just need this to get over an initial hurdle.

Riccardo Bucco · Accepted Answer · 2020-07-12 10:53:48Z

0

You can use the eval() function like so:

 def run(self, command):
    return eval(command)

would this work for you?

edited Jul 12, 2020 at 10:53

Riccardo Bucco

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answered Jul 12, 2020 at 10:45

Bhavye Mathur

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4 Comments

PrestonDocks Over a year ago

No I get an error, saying that random_number is not a member of the Job Object

kaktus_car Over a year ago

What @Bhavye Mathur said works for me, no error. But the security of the eval could the potential problem

PrestonDocks Over a year ago

@kaktus_car Thanks for the warning, always better to be safe than sorry, so I do a check of the commands first before I run them.

kaktus_car Over a year ago

@PrestonDocks You're welcome, I agree, especially if you are evaluating user inputs

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