Dynamically running python code on google app engine

Question

I am trying to be able to dynamically run python code, with variables being able to be passed through to the code. I was able to do this on my computer before I added my project to the google app engine environment (because I can access all the files, but now, with google app engine, I can not do that.

I am struggling to find a solution to this problem. It does not need to be too terribly fancy, just send variables in and get html out, as well as scripts being able to be added client side (the crucial part) to whatever database method that is used.

Edit: well basically what I mean by dynamically is so that I can import (or thats what I did in IDLE when I tested the prototype, the solution will probably not be called importing) a python script with the name of the library being stored in a variable, as well as an unknown number of variables that would be added. I got this to work on Idle, but now I need to get it to work in the google app engine environment, and people need to be able to upload scripts as well (which is the main problem that cascades into many more problems)

Edit: When I say that I managed to get this to work on my local machine, I mean I was able to manually drop scripts into the same directory as my main script. The script would later import and execute the scripts when necessary. I was able to get this to work with the following code:

#calling function
mod = __import__('actions.'+folder+'.'+FILE)
VAR = getattr(getattr(mod, folder), FILE)
response = VAR.Main()
print response

This code worked on both my laptop and in the google app engine environment, But When I try to add more scripts to the directory is when things get problematic. On my laptop I could just move the file over one way or another because I had full access to the file directory. On Google App engine I do not have the ability to just upload a file to the same directory or subdirectory of the rest of my python scripts. So basically the problem comes up when trying to design a way to allow more code to come into the system (in my case, adding more 'plugins').

Yes. I have gotten the blob store to work, the datastore to work. But I do not know how to dynamically run code. — bs7280
– bs7280, Commented Sep 29, 2012 at 19:57
Well if you want people to upload their own scripts and have them execute in the app engine enviroment then that's not possible afaik. Only you can do that, when you deploy your app. — Paul Collingwood
– Paul Collingwood, Commented Sep 29, 2012 at 20:42

Guido van Rossum · Accepted Answer · 2012-10-01 01:22:42Z

2

The answer is the exec statement (also known as the exec() function) or the eval() function. See http://docs.python.org/reference/simple_stmts.html#the-exec-statement and http://docs.python.org/library/functions.html?highlight=eval#eval. These can execute arbitrary Python code from a string. exec() runs a script and you get the side effects; eval() takes an expression and returns its value. Typically you pass input in as variables in the local namespace.

answered Oct 1, 2012 at 1:22

Guido van Rossum

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bs7280 · Accepted Answer · 2012-10-01 20:04:12Z

Ok, So what I eventually did was use the datastore to upload everything such as the name, description, uploader and code of the plugin (for now the code is just entered into a textarea box). I then, instead of importing a file located in a folder under the same directory of my code like I had before when running everything off of my desktop, Imported the plaintext code into a module using this little bit of magic:

#Initiating Variables for use by importing functions
module_name = 'mymod'
filename = 'action_file'
source = PossibleMatches[0][1] #the source code from the best matched option

# define module_name somewhere
import types
module = types.ModuleType(module_name)

# source should the code to execute
# filename should be a pseudo-filename that the code's from
# (it doesn't actually have to exist; it's used for error messages)
code_object = compile(source, filename, 'exec')

#execute the code in the context of the module
exec code_object in module.__dict__

#Executing the 'Main' Function from the code
return module.Main()

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