<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def get_env_key(obj, key=None):
 """ Return environment variable key to use for lookups within a namespace represented by the package name. For example, any varialbes for predix.security.uaa are stored as PREDIX_SECURITY_UAA_KEY """

    return str.join('_', [obj.__module__.replace('.','_').upper(),
        key.upper()])