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#uni... (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@btinternet.com* Twitter : *@TonyFlury https://twitter.com/TonyFlury/*