[Python-Dev] Review of Pull Request 5974 please

[Yury Selivanov]

Reviewed. This seems to be an omission that needs to fixed, thanks for the
PR! Almost good to go in 3.8. As for 3.7, this isn't a bug fix it's up to
Ned if he wants to accept it.

Yury
On Sun, Apr 29, 2018 at 8:02 AM Anthony Flury via Python-Dev <
python-dev at python.org> wrote:

> All,

> Can someone please review Pull Request 5974
> <https://github.com/python/cpython/pull/5974> on Python3.8 - the Pull
> request was submitted on 4th March - this pull request is associated
> with bpo-32933 <https://bugs.python.org/issue32933>

> To summarize the point of this pull request:

> It fixes a bug of omission within mock_open
> <
https://docs.python.org/3/library/unittest.mock.html?highlight=mock_open#unittest.mock.mock_open

> (part of unittest.mock)

> The functionality of mock_open enables the test code to mock a file
> being opened with some data which can be read. Importantly, mock_open
> has a read_data attrribute which can be used to specify the data to read
> from the file.

> The mocked file which is opened correctly supports file.read(),
> file.readlines(), file.readline(). These all make use of the read_data
> as expected, and the mocked file also supports being opened as a context
> manager.

> But the mock_open file does not support iteration  - so pythonic code
> which uses a for loop to iterate around the file content will only ever
> appear to iterate around an empty file, regardless of the read_data
> attribute when the mock_open is created

> So non-pythonic methods to iterate around the file contents - such as
> this :

>       data = opened_file.readlines()
>       for line in data:
>           process_line(line)

> and this :

>          line = opened_file.readline()
>          while line:
>                  process_line(line)
>                  line = opened_file.readline()

> Can both be tested with the mocked file containing simulated data (using
> the read_data attribute) as expected.

> But this code (which by any standard is the 'correct' way to iterate
> around the file content of a text file):

>       for line in opened_file:
>           process_line(line)

> Will only ever appear to iterate around an empty file when tested using
> mock_open.

> I would like this to be reviewed so it can be back-ported into Python3.7
> and 3.6 if at all possible. I know that the bug has existed since the
> original version of mock_open, but it does seem strange that code under
> test which uses a pythonic code structure can't be fully tested fully
> using the standard library.

> --
> Anthony Flury
> email : *Anthony.flury at btinternet.com*
> Twitter : *@TonyFlury <https://twitter.com/TonyFlury/>*

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-- 
          Yury