As long as we support Python 2.7 we have to support the different installation
methods (virtualenv) for Python 3 and Python 2.  For this purpose, a Makefile is
added with this patch, which can be removed later when Python 2.7 is no longer
supported (in the main line).

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

Some of the files in the repository have CRLF line ending other have LF ending.
This patch normalizes to unix-style (LF)::

    find . -type f -not -path './.git*' | xargs sed -i 's/\r//g'

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

Command to format the code [1]::

    python -m black .

Black version::

    $ python -m black --version
    python -m black, 24.3.0 (compiled: yes)
    Python (CPython) 3.12.2

HINT: Black removes some u'' strings that are Unicode in Python 2.x, these had
to be corrected manually.

[1] https://black.readthedocs.io/en/stable/#

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

This patch adds a pylint profile (.pylintrc) with the aim to have a good
compromise in context of Python v2 & v3 and the status of the current
implementation.

To avoid having to switch off all checks in the profile, many of the issues
reported by pylint were handled by using inline comments.

Simple errors in the code were corrected, but only if the effect of the change
was locally limited and manageable.

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

This patch disables issues reported by pylint in py3 that we have from the
py2 compatibility.

HINT:

    When py2 compatibility is abandoned, this commit can be reverted and the
    code passages can be converted to Py3.

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

The idiomatic way to perform an explicit typecheck in Python is to use
`isinstance(x, Y)` rather than `type(x) == Y`, `type(x) is Y`. [1]

[1] https://pylint.pycqa.org/en/latest/user_guide/messages/convention/unidiomatic-typecheck.html

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

Since the class `datetime.datetime` is a subclass of `datetime.date`, the
`isinstance` check is not suitable if a distinction has to be made between the
two classes.

The `type` check is more suitable in these cases, as no further inheritance can
be assumed for these two object classes and the code is also easier to read in
the context of this distinction.

The situation is completely different with method:

- icalendar.Trigger.transformFromNative()

in this method (in the Trgger class) a distinction is made between a date and a
time duration.  Since `datetime.date` is the base class, it is suitable for an
`isinstance` check of a date object (which can be an instance of the
`datetime.datetime` class as well as `datetime.date`).

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

The tests._test() function has been removed in commit b564a07 / remove
obsolte code.

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

The base class `vobject.base.Component` defines method's prototype by:

    def prettyPrint(self, level=0, tabwidth=3):
        ...

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

…lint (W1113)

1. When defining a keyword argument before variable positional arguments, one
can end up in having multiple values passed for the aforementioned parameter in
case the method is called with keyword arguments[1].

2. In the methods:

- icalender.VCalendar2_0.serialize
- icalender.VTimezone.validate
- icalender.VEvent.validate
- icalender.VTodo.validate
- icalender.VAlarm.validate
- icalender.VAvailability.validate
- icalender.Available.validate

the "arguments-differ (W0221)" [2] message from pylint had to be disbaled.  This
message is a direct consequence of the "keyword-arg-before-vararg (W1113)" issue
already present in the base class.

3. in method:

- vcard.Photo.serialize

the "signature-differs (W0222)" [3] message from pylint had to be disbaled (for same
reason as mentioned in 2.)

---

HINT:
  It is advisable to correct the parameter definitions in a follow-up PR.

[1] https://pylint.pycqa.org/en/latest/user_guide/messages/warning/keyword-arg-before-vararg.html
[2] https://pylint.pycqa.org/en/latest/user_guide/messages/warning/arguments-differ.html
[3] https://pylint.pycqa.org/en/latest/user_guide/messages/warning/signature-differs.html

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

Adding the checks to the github workflow for PRs ensures that future PRs cannot
be merged before they have passed the quality gate.

The tests can be carried out locally as follows (see README.md)::

    $ make format pylint test

The github workflows do not support Python 2 versions, the py2 quality gate can
therefore only be tested locally and requires a Python 2 runtime (the Makefile
assumes asdf is installed / as described in the README.md)::

    $ make clean venv2.7 test pylint2.7

CAUTION:

  There are no automated tests for Python 2 on github, the downward compatible
  0.9.x releases have to be tested locally !!!

About tools of the quality gate
===============================

- Tools such as the code formatting of black are version-dependent / new rules
  are implemented with each new version of the tool.  To ensure that the same
  rules always apply to the quality gate, the versions of the tools must be
  pinned::

    black ==24.3.0; python_version >= "3.8"  # (newest) Black up from py3.8
    pylint ==3.1.0; python_version >= "3.8"  # (newest) Pylint up from py3.8
    pylint ==1.9.5; python_version =="2.7"   # old Pylint in py2.7

- Since we support Python versions that have reached their EOL (py2.7 & Py3.7)
  we cannot add the tools of the quality gate to every python version we want
  to support / see remarks about the tools below.

CAUTION:

  Upgrading the version of one of these tools must always be done in a
  separate PR / could be automated by tools like Renovate or Dependabot.

About Black
===========

- Black is not supported in py2 and py3.7 support stopped in Black v23.7.0.
  Since the Black test is already executed in other Python versions, a further
  test in py3.7 can be omitted.

- We use black started from current version 24.3.0

About Pylint
============

- py2.7: latest pylint version for py2 is pylint v1.9.5

- py3.7: since the Python test is already executed in other Python versions, a
  further test in py3.7 can be omitted.

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>