Create an import statement using variable “interpolation”

问题

I have a long list of possible files I need to import. I will only ever need 1 of them and they all have the same interface. (Choosing a payment gateway to process a payment)

Suppose I have a dictionary that represents the name of all the gateway files.

i.e.

gateways = {
   '1' : 'authorize',
   '2' : 'paysimple',
   '3' : 'braintreepayments',
   '4' : 'etc',
}

I know the keys to this dictionary based on information from a database. So, if I receive a payment process request with a gateway value of 1 I know it needs to be handled by Authorize.net. A 2 is to be processed by Pay Simple. Etc.

I'd like to be able to create an import statement that is built with the information I know rather than a horrible list of elif statements.

Consider the simple method below:

# For the purposes of this example assume payment_gateway is defined
# elsewhere and represents the key to the dictionary
gateway_file = gateways.get(payment_gateway)

import_str = "from gateway_interface.%s import process" % gateway_file
gogo(import_str)

Where gogo is a way to cause the import statement to actually import.

Is such a thing possible?

回答1:

Simplest

process = __import__('gateway_interface.'+gateway_file,fromlist=['foo']).process

EDIT: 'foo' in the fromlist can be anything, as long as fromlist is not an emptylist. That little bit of strangeness is explained in Why does Python's __import__ require fromlist?.

I also had to edit because in my first post __import__ didn't work as expected as further described in Python's __import__ doesn't work as expected.

if you have python 2.7

import importlib
process = importlib.import_module('gateway_interface.'+gateway_file).process

WAAAAY cool would be to use package_tools (e.g. from pkg_resources import iter_entry_points)

That could give you a solution to find the right function even if they are in odd packages not under gateway_interface. If they are all on one place and you don't need the sytle-point that is overkill so ... yeah just __import__

回答2:

Take a look at the imp module which allows you to access the internals of the import statement, or the __import__ method itself - either of these should allow you to achieve what you describe I think.

回答3:

The builtin __import__ method should work:

process = __import__(gateways.get(payment_gateway)).process

来源：https://stackoverflow.com/questions/11404617/create-an-import-statement-using-variable-interpolation

标签

python

import

string-interpolation