We have a scenario where we need to make assignments to fields using the method 

> put(String, Object)

Ref:
https://developer.salesforce.com/docs/atlas.en-us.apexcode.meta/apexcode/apex_methods_system_sobject.htm#apex_System_SObject_put

Once in a managed package the assignment:

    String oldDesc = (String)acc.put('Custom_Field__c', 'some value');

will fail, because the packaged field will have a namespace prefix. So if it's been packaged as 

> 'mypackage'

, the correct put() call would be:

    String oldDesc = (String)acc.put('mypackage__Custom_Field__c', 'some value');

How can I avoid hard coding a package namespace?