classification
Title: Add __iter__ support for mock_open
Type: behavior Stage: patch review
Components: Library (Lib) Versions: Python 3.6, Python 3.5, Python 3.4
process
Status: open Resolution:
Dependencies: Superseder:
Assigned To: michael.foord Nosy List: Arve.Knudsen, José.Luis.Lafuente, berker.peksag, gms, kushal.das, michael.foord, mucka, pkoning
Priority: normal Keywords: patch

Created on 2014-04-16 17:56 by michael.foord, last changed 2017-01-15 09:32 by gms.

Files
File name Uploaded Description Edit
213.patch michael.foord, 2014-04-16 17:56
mock.diff pkoning, 2014-06-12 17:44 Patch for bug review
testwith.diff pkoning, 2014-06-12 19:02 mock_open test suite patch review
mock_new.diff mucka, 2015-01-29 18:35 review
Messages (6)
msg216522 - (view) Author: Michael Foord (michael.foord) * (Python committer) Date: 2014-04-16 17:56
mock_open returns a mock object suitable for using as a mock file handle. File handles support iteration, so mock_open should support that. If possible it should be integrated with the current read/readlines support (only if possible), so the suggested patch may not be enough.


1.    Want to mock this:
with open(source_file, 'r') as f:             
    for line_num, line_text in enumerate(f):
        print line_text

2.  Tried this:
with patch('__builtin__.open', mock_open(read_data='text'), create=True) as p:

3.  enumerate causes a call to __iter__() which is not handled by the mock_open code.


What is the expected output? What do you see instead?

The __iter__ is allowed on the returned file handle

What version of the product are you using? On what operating system?

latest

Please provide any additional information below.

Patch would have mock_open setup handle.__iter__.return_value to a passed in parm or if none, possibly a iter(StringIO(read_data)) on the existing read_data parm to keep the interface unchanged.
msg220371 - (view) Author: Paul Koning (pkoning) Date: 2014-06-12 17:44
I created a fix for this.  This also fixes a second issue in mock_open, which is that readline() raises StopIteration at EOF rather than returning empty strings.  See attached diff.
(Is there a  better procedure for submitting fixes?)
msg220373 - (view) Author: Paul Koning (pkoning) Date: 2014-06-12 19:02
This is the corresponding patch to the test suite.
msg222279 - (view) Author: Arve Knudsen (Arve.Knudsen) Date: 2014-07-04 11:58
I noticed this issue too, thanks for fixing it!
msg234985 - (view) Author: Maciej Zagrabski (mucka) * Date: 2015-01-29 18:35
Provided path did not work for me. Probably because lack of __next__ handler. I noticed that issue when interacting with cvs.reader and cvs.DictReader. After simple modification it seems to work fine.
msg285508 - (view) Author: Georg Sauthoff (gms) Date: 2017-01-15 09:32
For working around this issue on Python 3.5 it is sufficient to overwrite just the `return_value.__iter__` method of the object returned by `mock_open()` with an iterator that calls the mocked `readline()` method until it returns the empty string.

cf. e.g. https://github.com/gsauthof/utility/blob/6489c7215dac341be4e40e5348e64d69461766dd/user-installed.py#L176-L179

This also works in combination with `csv.reader()`, i.e. when calling it with the mocked file object.
History
Date User Action Args
2017-01-15 09:32:05gmssetmessages: + msg285508
2017-01-15 09:05:03gmssetnosy: + gms
2015-12-14 16:44:23José.Luis.Lafuentesetnosy: + José.Luis.Lafuente
2015-07-17 22:21:43berker.peksagsetnosy: + berker.peksag

versions: + Python 3.6
2015-01-29 18:35:30muckasetfiles: + mock_new.diff
versions: + Python 3.4
nosy: + mucka

messages: + msg234985
2014-07-04 11:58:25Arve.Knudsensetmessages: + msg222279
2014-07-04 11:53:28Arve.Knudsensetnosy: + Arve.Knudsen
2014-06-12 19:02:59pkoningsetfiles: + testwith.diff

messages: + msg220373
2014-06-12 17:44:26pkoningsetfiles: + mock.diff
nosy: + pkoning
messages: + msg220371

2014-04-16 17:56:45michael.foordcreate