Everyone knows and loves Python’s import function. This function is used to import external modules into the current module/script we are writing. Here are a few simple examples illustrating how the function can be used:
| # import a specific module | |
| from vehicle.four_wheels import car | |
| my_car = car.Car(transmission="automatic") | |
| # import a specific class within a module | |
| from vehicle.four_wheels.car import Car | |
| my_car = Car(transmission="automatic") | |
| # import everything from a module into the current namespace | |
| from vehicle.four_wheels import * | |
| my_car = Car(transmission="automatic") | |
| my_bus = Bus(color="Yellow") |
Internally, a call to the import function makes a call to the built-in __import__ function. However, there are 2 cases where using import would not work and the only way out is to call __import__ ourselves.
The most common case where we would have to call __import__ directly would be when we want to import specific modules at run-time based on user input. Here is how we might do that:
| # global scope these variables so that | |
| # we can use them throughout our code | |
| Car = None | |
| Bus = None | |
| # | |
| # exciting stuff happening here | |
| # | |
| # now, based on the variable vehicle | |
| # we want to import a specific module | |
| if vehicle == "car": | |
| # equivalent to: from vehicle.four_wheels.car import Car | |
| _Car = __import__("vehicle.four_wheels.car", globals(), locals(), ["Car"]) | |
| Car = _Car.Car | |
| if vehicle == "bus": | |
| # equivalent to: from vehicle.four_wheels.bus import Bus | |
| _Bus = __import__("vehicle.four_wheels.bus", globals(), locals(), ["Bus"]) | |
| Bus = _Bus.Bus | |
Yes, I know that we didn’t really have to import at run-time in the previous example. It was just meant to be a simple example 🙂
Another case where we might have to call __import__ is when, for some reason, the parent modules/folders for a module we want to import or a module itself has a name with characters that are not allowed by Python. For example, something like the snippet below would not work:
| # this does not work! | |
| from vehicles.four–wheels.car import Car |
Notice how the hyphen is not allowed in the module name. Here is how we might work around that:
| # this works! | |
| _Car = __import__("vehicles.four-wheels-car", globals(), locals(), ["Car"]) | |
| Car = _Car.Car |
