classification
Title: Have importlib.reload() raise ImportError when a spec can't be found
Type: enhancement Stage:
Components: Library (Lib) Versions: Python 3.7
process
Status: open Resolution:
Dependencies: Superseder:
Assigned To: Nosy List: Richard Cooper, brett.cannon, eric.snow, ncoghlan
Priority: low Keywords: easy

Created on 2017-03-19 00:09 by Richard Cooper, last changed 2017-03-20 19:22 by brett.cannon.

Files
File name Uploaded Description Edit
bug.py Richard Cooper, 2017-03-19 00:09 Repo testcase
Messages (2)
msg289834 - (view) Author: Richard Cooper (Richard Cooper) Date: 2017-03-19 00:09
importlib.reload doesn't work; gives an error about NoneType having no name attribute.

See attached a simple repo testcase

When run it yields the following [disappointing] result.  I'm running Python3.0.6.1 (installed from brew) on OSX 10.12.3

```
iMac:python_package_loader cooper$ python3 bug.py 
module loaded
Traceback (most recent call last):
  File "bug.py", line 14, in <module>
    importlib.reload(sys.modules[moduleName])
  File "/usr/local/Cellar/python3/3.6.0_1/Frameworks/Python.framework/Versions/3.6/lib/python3.6/importlib/__init__.py", line 166, in reload
    _bootstrap._exec(spec, module)
  File "<frozen importlib._bootstrap>", line 589, in _exec
AttributeError: 'NoneType' object has no attribute 'name'
```
msg289903 - (view) Author: Brett Cannon (brett.cannon) * (Python committer) Date: 2017-03-20 19:22
First, I don't know what version you're testing against because 3.0.6.1 isn't an actual release of Python and 3.6.1 isn't released yet (unless you know something I don't know :) ).

Second, the issue is that you're trying to import a module under a name which doesn't match the file specified. That's causing reload() to not be able to find the original source file to reload against, leading to the None being returned by importlib._bootstrap._find_spec() which is leading to the error you're seeing. (Remember, reload() basically runs like an import statement for the module you're reloading but recycles the module object.)

Third, while an exception is reasonable in this case, it is misleading and reload() should be updated to raise an ImportError if _bootstrap._find_spec() returns None.

I'm marking this issue as an easy fix since you just need to add an `is None` check on a return value and then raise ImportError if necessary in case someone wants to propose a PR to improve the error. It will require a doc update to document the change in the exception raised.
History
Date User Action Args
2017-03-20 19:22:29brett.cannonsetpriority: normal -> low

type: crash -> enhancement

title: importlib.reload references None object -> Have importlib.reload() raise ImportError when a spec can't be found
keywords: + easy
nosy: + brett.cannon, ncoghlan, eric.snow
versions: + Python 3.7
messages: + msg289903
2017-03-19 00:09:56Richard Coopercreate