Using a variable for an import

Question

I have the following pattern:

databasename = "mydatabase"
import databasefunctions

and in databasefunctions I have the following method.

def checkStatusOfDatabase(database=databasename):

I however get an error saying: NameError: name 'databasename' is not defined on the line defining checkStatusOfDatabase.

I could of course just move the definition of databasename inside the databasefunctions module, but that would not be suitable in my design. How else can I achieve that the databasename defined in the main module is utilized as the default in any imported modules.

• aodj: Out of curiosity, why are you unable to do the definition in the databasefunctions module?
• viraptor: Not an exact duplicate, but this should answer your question to some extent: stackoverflow.com/questions/67631/…
• David: I would like to have all the parameter values right in the beginning of my main module (because I modify them a lot) and not hidden away in different imported modules.
• David: @viraptor. That answer is related but does not help me as I am already definining the variable before I import, but that does not help.
• viraptor: sorry, I misunderstood your question - I read it as if you were trying to load a module called "mydatabase"... You're right it does not answer the question.

Answer 1

You cannot (and should not) do that; doing so would make it impossible to just import databasefunctions without the main module. However, you can implement a default like this:

# databasefunctions
DEFAULT_NAME = ""
def checkStatusOfDatabase(database=DEFAULT_NAME):
# main
import databasefunctions
databasefunctions.DEFAULT_NAME = "mydatabase"

• David: What an excellent answer! I can accept it in 4 minutes (Stackoverflow obviously does not believe in quick correct answers!?).
• David: Could I write the following in main instead: from databasefunctions import * and then on the following line just: DEFAULT_NAME = "mydatabase"
• slowdog: phihap: Unfortunately, you can do that, by writing from __main__ import databasename in the databasefunctions module. But I absolutely agree that you should not, and your alternative is the Right Way.
• slowdog: David: That would not work because the assignment DEFAULT_NAME = "mydatabase" only makes the name DEFAULT_NAME refer to something different within your main module. The assignment databasefunctions.DEFAULT_NAME = "mydatabase", on the other hand, changes the meaning of DEFAULT_NAME within the databasefunctions module. It's a subtle distinction, and surprising if you're used to other languages, like C, where assignments modify objects.

Answer 2

You can use the __builtin__ module

import __builtin__
__builtin__.foo = 'bar'

This will then be accessible from all other modules when you do a similar access method. You could use this and do this:

import __builtin__
dbName = __builtin__.get('foo', 'ham') # dictionary access with default return
def checkStatusOfDatabase(database=dbName):
 ...

• aodj: I'd like to stress that whilst this works, it's not very wise.