Import file using string as name

Question

Possible Duplicate:
Dynamic module import in Python

I intend to make a suite of files at some point soon, and the best way to organize it is to have a list, that list will be at the very top of a file, and after it will come a ridiculous amount of code to handle what that list controls and how it operates. I'm looking to write said list only once, and said list is a list of folder and file names in this format:

[(folder/filename, bool, bool, int), (folder/filename, bool, bool, int)]

As you can see, folder/filename are the same (sort of). File name is folder name with .py on the end, but doing import XXX you don't need to do import XXX.py, so I don't see this causing an issue.

The problem I'm facing is importing using this method...

for (testName, auto, hardware, bit) in testList:
    print(testName)
    paths = "\\" + testName
    print paths
    addpath(paths)
    sys.modules[testName] = testName # One of a few options I've seen suggested on the net
    print("Path Added")
    test = testName + ".Helloworld()"
    eval(test)

So for each test I have, print the name, assemble a string which contains the path ("\\testName"), for this example, print the test path, then add the path to the list (sys.path.append(path)), then print to confirm it happened, then assemble a string which will be executed by eval for the tests main module and eventually eval it.

As you can see, I'm currently having to have a list of imports at the top. I can't simply do import testName (the contents of testName are the name of the module I wish to import), as it will try to find a module called testName, not a module called the contents of testName.

I've seen a few examples of where this has been done, but can't find any which work in my circumstances. If someone could literally throw a chunk of code which does it that would be wonderful.

I'd also request that I'm not hung, drawn, nor quartered for use of eval, it is used in a very controlled environment (the list through which it cycles is within the .py file, so no "end user" should mess with it).

Note that the indentation is correct in ST, for some reason I think this website just doesn't like parsing my text correctly :( — XtrmJosh, Dec 28 '12 at 14:39
Python already has a way of managing large collections of `.py` files that you might want to import, which understands folders and subfolders, lets you handle relative imports, does namespacing properly, and so on. It's called a [package](http://docs.python.org/2/tutorial/modules.html#packages). Is there a reason you don't want to use one? — Katriel, Dec 28 '12 at 14:50
duplicate also of: http://stackoverflow.com/questions/8718885/import-module-from-string-variable — 0 _, Jun 23 '15 at 16:23

score 66 · Accepted Answer · edited Dec 05 '18 at 11:12

66

Not sure if I understood everything correctly, but you can import a module dynamically using __import__:

mod = __import__(testName)
mod.HelloWorld()

Edit: I wasn't aware that the use of __import__ was discouraged by the python docs for user code: __import__ documentation (as noted by Bakuriu)

This should also work and would be considered better style:

import importlib

mod = importlib.import_module(testName)
mod.HelloWorld()

edited Dec 05 '18 at 11:12

answered Dec 28 '12 at 14:45

lbonn

2,499
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Marvelous, thanks a ton for this, spent well over an hour scouring for information on it, I managed to write out __import__(testName) earlier, but didn't realise I had to assign the response to a module or w.e, fortunately all my functions will be named Test throughout all files, so I can just call mod.Test() from now on. – XtrmJosh Dec 28 '12 at 14:50
@XtrmJosh have you seen the other answer? `__import__` is an implementation detail; you should use `importlib` (or `imp` if you don't care about Python 3.x compatibility). – Katriel Dec 28 '12 at 14:54
1

What kind of values are allowed for testName? Do I put `.py` at the end? Do I provide a relative path or an absolute path? – Aaron Franke Jul 17 '22 at 22:22
1

Aaron lead me to the solution to my problem. I added `.py` to `testName`. This does not work. Use your file name without extension! – Peter Oct 13 '22 at 08:53

score 24 · Answer 2 · answered Dec 28 '12 at 14:47

24

Never, ever, ever mess with sys.modules directly if you don't know exactly what you are doing.
There are a lot of ways to do what you want:
1. The build-in __import__ function
2. Using imp.load_module
3. Using importlib.import_module

I'd avoid using __import__ directly, and go for importlib.import_module(which is also suggested at the end of the documentation of __import__).

answered Dec 28 '12 at 14:47

Bakuriu

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This is for `import moduleName` where moduleName is string. How about `from moduleName import *` ? – Nam G VU May 30 '17 at 06:57
2

@NamGVU try to import the module as above and then: `globals().update(module.__dict__)` – Bakuriu May 30 '17 at 07:10
I just found another solution here which import only the user-defined variables https://stackoverflow.com/a/31306598/248616 – Nam G VU May 30 '17 at 07:50
2

Where can I find examples of how to do this? I want to run methods defined in Python scripts in subfolders. Do I provide a relative path? Absolute path? Do I put a `.py` suffix? – Aaron Franke Jul 17 '22 at 22:24

score 2 · Answer 3 · answered Dec 28 '12 at 14:55

Add the path where module resides to sys.path. Import the module using __import__ function which accepts a string variable as module name.

import sys
sys.path.insert(0, mypath)  # mypath = path of module to be imported
imported_module = __import__("string_module_name") # __import__ accepts string 
imported_module.myfunction()   # All symbols in mymodule are now available normally

Import file using string as name

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