Have importlib.reload() raise ModuleNotFoundError when a spec can't be found

[richardcooper]

BPO	29851
Nosy	@brettcannon, @ncoghlan, @ericsnowcurrently, @serhiy-storchaka
PRs	bpo-29851: Have importlib.reload() raise ImportError if the module's spec is not found #972
Files	bug.py: Repo testcase

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

Show more details

GitHub fields:

assignee = None
closed_at = <Date 2017-05-24.22:20:40.688>
created_at = <Date 2017-03-19.00:09:56.344>
labels = ['3.7', 'easy', 'type-feature', 'library']
title = "Have importlib.reload() raise ModuleNotFoundError when a spec can't be found"
updated_at = <Date 2017-05-24.22:20:40.688>
user = 'https://bugs.python.org/RichardCooper'

bugs.python.org fields:

activity = <Date 2017-05-24.22:20:40.688>
actor = 'brett.cannon'
assignee = 'none'
closed = True
closed_date = <Date 2017-05-24.22:20:40.688>
closer = 'brett.cannon'
components = ['Library (Lib)']
creation = <Date 2017-03-19.00:09:56.344>
creator = 'Richard Cooper'
dependencies = []
files = ['46737']
hgrepos = []
issue_num = 29851
keywords = ['easy']
message_count = 5.0
messages = ['289834', '289903', '291081', '291125', '294405']
nosy_count = 5.0
nosy_names = ['brett.cannon', 'ncoghlan', 'eric.snow', 'serhiy.storchaka', 'Richard Cooper']
pr_nums = ['972']
priority = 'low'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue29851'
versions = ['Python 3.7']

[richardcooper]

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'

[brettcannon]

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.

[serhiy-storchaka]

Wouldn't ModuleNotFoundError be more appropriate?

[brettcannon]

That's a good point, Serhiy, since that's what the exception is signaling. So yes, the exception should be ModuleNotFounderror.

[brettcannon]

New changeset 9498782 by Brett Cannon (Garvit Khatri) in branch 'master':
bpo-29851: Have importlib.reload() raise ImportError if the module's spec is not found (GH-972)
9498782