Robot Framework - Not able to call Python function

Well, you really just need to read the error message:

'return_random_number' is not defined nor importable as module

But the question is how to go from here.

First off, it's good to start with reading the official documentation, specifically how to create custom libraries and use such keywords in your RF files.

After doing so, you'll find out several problems:

• custom libraries have a certain scope, so you should write it in there (choose the right for your case, I don't know which scope you need, so I'll randomly pick one):

from random import random

class RawData:

    ROBOT_LIBRARY_SCOPE = 'TEST CASE'

    def return_random_number(self):
        return random()

• your Python module/library won't be executed as a standalone Python script, so you can delete the last 3 lines:

raw_data = raw_data()
number = raw_data.return_random_number()
print(number)

So, your custom library should look like:

RawData.py

from random import random

class RawData:

    ROBOT_LIBRARY_SCOPE = 'TEST CASE'
    ROBOT_LIBRARY_VERSION = 1.0

    def return_random_number(self):
        return random()

You can also add library version. It's recommended, it's a good practice.

Now, you want to import your library in RF:

*** Settings ***
Library     RawData.py

I don't know why you're calling it RawData when in fact it returns a random number. Consider using proper names.

Then you want to call your custom keyword. Custom keywords created in custom libraries could be called by simply typing the names of the Python methods without underscores, so you don't need any Evaluate keyword, you can just call your custom keyword like this:

${result}=    Return Random Number