How to change external objects in the python code of the executable in exec()?

Question

Python

There is this code:

def executeRule(stdout, rule):
  obj = None
  try:
    parsedJson = json.loads(stdout)
    pyCmd = 'obj = parsedJson' + rule
    exec( pyCmd  )
  except BaseException as e:
    print( e, file=sys.stderr)
  return obj

Here:
rule is a string obtained from com arguments. lines sys.argv[2]
stdout is the output obtained as a result of launching the console tool. After parsing stdout,
I need to convert it into familiar data structures in python and get a value from them. The whole point is that I need to get on the basis of what was passed in the com. line.
The problem is that after exec() obj does not change and continues to be set to None. Although if you write code without exec, but directly, then the value is pulled out and it is in the parsed json!
How to organize a subject? What is the problem?
PS:
I'm starting to work on python Toko Toko

Answer 1

In exec and eval, you can directly set global and local variables: eval(expression[, globals[, locals]])

>>> obj = None
>>> exec("obj = 2", {}, locals())
>>> print obj
2

Answer 2

Correct, because exec is executed in a different namespace. Try like this:

obj = None
exec("""import random; global obj; obj = random.random(); obj *= 100;""")
print(obj)