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[Python-Dev] Review of Pull Request 5974 please

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.

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
> <

> (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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