Add a recipe in unittest.mock examples about mock_open per file

[tirkarthi]

BPO	38157
Nosy	@cjw296, @voidspace, @lisroach, @mariocj89, @tirkarthi
PRs	bpo-38157: Add example about per file output for mock_open. #16090

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

Show more details

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2019-09-13.10:54:43.734>
labels = ['3.8', 'type-bug', '3.7', '3.9', 'docs']
title = 'Add a recipe in unittest.mock examples about mock_open per file'
updated_at = <Date 2019-09-13.11:44:22.369>
user = 'https://github.com/tirkarthi'

bugs.python.org fields:

activity = <Date 2019-09-13.11:44:22.369>
actor = 'xtreak'
assignee = 'docs@python'
closed = False
closed_date = None
closer = None
components = ['Documentation']
creation = <Date 2019-09-13.10:54:43.734>
creator = 'xtreak'
dependencies = []
files = []
hgrepos = []
issue_num = 38157
keywords = ['patch']
message_count = 1.0
messages = ['352285']
nosy_count = 6.0
nosy_names = ['cjw296', 'michael.foord', 'docs@python', 'lisroach', 'mariocj89', 'xtreak']
pr_nums = ['16090']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue38157'
versions = ['Python 3.7', 'Python 3.8', 'Python 3.9']

[tirkarthi]

With bpo-37669 it was proposed to refactor out the mock_open handler to return different mocks per file and an API change to make sure read_data accepts a dictionary of file and return values it can only land on master if accepter. It's already possible now with using side_effect to return per file content. Adding it would be a good example like below so that users can know this usage. I can prepare a PR for this.

from unittest.mock import mock_open, patch

DEFAULT_MOCK_DATA = "default mock data"
data_dict = {"file1": "data1",
             "file2": "data2"}

def open_side_effect(name):
    return mock_open(read_data=data_dict.get(name, DEFAULT_MOCK_DATA))()

with patch(f"{__name__}.open", side_effect=open_side_effect):
    with open("file1") as file1:
        assert file1.read() == "data1"

        with open("file2") as file2:
            assert file2.read() == "data2"

            with open("file1") as file3:
                assert file3.read(1) == "d"

    assert [file1](https://bugs.python.org/file1).read() == ""

    with open("defaultfile") as file4:
        assert file4.read() == "default mock data"

[hugovk]

Fixed via #16090 and backports to 3.11. Thanks all!