[2.7] bpo-32524: Don't leak a package's __init__.py module object in sys.modules on SyntaxError

[segevfiner]

With the file hello/__init__.py:

ham = 123
spam()spam()

I get the following:

Python 2.7.14 (v2.7.14:84471935ed, Sep 16 2017, 20:19:30) [MSC v.1500 32 bit (Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import hello
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "hello\__init__.py", line 2
    spam()spam()
             ^
SyntaxError: invalid syntax
>>> import hello
>>> print hello
<module 'hello' from 'hello'>
>>> print dir(hello)
['__doc__', '__file__', '__name__', '__package__', '__path__']
>>>

I'd expect to get the SyntaxError twice, which is indeed what happens on at least Python 3.6 (Possibly earlier Python 3 versions).

Originally found here pallets/flask#2423 & pallets/flask#2588

cc @davidism @mitsuhiko

https://bugs.python.org/issue32524