Python packaging-related fixes:

* improved the docs on installing python runtime
* fixed the links to kaitaiStructCompile.setuptools
* added more examples of usage of kaitaiStructCompile.setuptools

lang_python.adoc

@@ -13,98 +13,140 @@ To generate Python modules, Kaitai Struct compiler should be invoked with
 `-t python` option:
 
 [source,shell]
-kaitai-struct-compiler -t python my_spec.ksy
+kaitai-struct-compiler -t python --python-package . my_spec.ksy
 
 This normally generates `my_spec.py` parser module, which is compatible
-with both Python 2 and 3.
+with both Python 2 and 3. It is strongly recommended to use python 3
+because python 2 is EOL since 2020-01-01. You can also install
+`python-is-python3` on Ubuntu focal to make `python3` be used via
+`python` command.
+
+`--python-package` optional CLI arg allows you to select a parent package
+name used by one generated file to import symbols from another one.
+
+If you want to embed KSC-generated files into an own package, it is
+recommended to set the arg to `.`, which means "current package",
+rather than to the real  name of the subpackage, because setting it
+to a real name will cause breakage when you (or anyone else) want
+to reorganize or rename your package. It will cause KSC generate
+relative imports instead of absolute ones for the specs imported into
+your main spec:
+
+----
+from .your_imported_spec import YourImportedSpec
+----
+
+(note the dot we have passed as an arg) instead of
+
+----
+from your_imported_spec import YourImportedSpec
+----
+.
+
+**Without setting this arg at all you will likely get an `ImportError`,
+if any of the specs imports another spec.** You can instead set this
+arg to the absolute path of the submodule, but it opens a can of worms.
+
+It is also recommended to put all the KSC-generated code into an
+own subpackage, in example `kaitai`, so, if your build process
+regenerates the files on every build, you could just .gitignore that dir.
 
-TODO: document `--python-package`
 
 [[add-runtime]]
 === Adding runtime library
 
 Code generated by Kaitai Struct compiler will require additional runtime
-library (https://pypi.org/project/kaitaistruct/[kaitaistruct at PyPi],
+library (https://pypi.org/project/kaitaistruct/[image:https://img.shields.io/pypi/v/kaitaistruct.svg[kaitaistruct at PyPi]],
 https://github.com/kaitai-io/kaitai_struct_python_runtime[sources at
 GitHub]).
 
 Runtime library API version must match compiler version that you're using
-(i.e. if you use ksc v0.8, then you must use compatible v0.8 runtime).
+(i.e. if you use ksc v0.9, then you must use compatible v0.9 runtime).
+
+If you are using snapshot KSC, you should also use snapshot runtime.
 
 [[add-runtime-release]]
 ==== Using release version
 
-With stable version of Kaitai Struct compiler, one can use use following
+With stable version of Kaitai Struct compiler, one can use the following
 methods:
 
 * On Debian / Ubuntu, one can install it from apt repositories:
 
-** For Python 2.x:
+** For Python 3.x:
 +
 [source,shell]
-sudo apt-get install python-kaitaistruct
+sudo apt-get install -y python3-kaitaistruct
 +
-Reference: https://packages.debian.org/buster/python-kaitaistruct[package info for Debian], https://packages.ubuntu.com/eoan/python-kaitaistruct[package info for Ubuntu]
+Reference: https://packages.debian.org/testing/python3-kaitaistruct[image:https://repology.org/badge/version-for-repo/debian_testing/python:python-kaitaistruct.svg[package info for Debian]], https://packages.ubuntu.com/focal/python3-kaitaistruct[image:https://repology.org/badge/version-for-repo/ubuntu_20_04/python:python-kaitaistruct.svg[package info for Ubuntu]]
 
-** For Python 3.x:
+** For Python 2.x:
 +
 [source,shell]
-sudo apt-get install python3-kaitaistruct
+sudo apt-get install -y python-kaitaistruct
 +
-Reference: https://packages.debian.org/buster/python3-kaitaistruct[package info for Debian], https://packages.ubuntu.com/eoan/python3-kaitaistruct[package info for Ubuntu]
+Reference: https://packages.debian.org/stable/python-kaitaistruct[image:https://repology.org/badge/version-for-repo/debian_stable/python:python-kaitaistruct.svg[package info for Debian]], https://packages.ubuntu.com/focal/python-kaitaistruct[image:https://repology.org/badge/version-for-repo/ubuntu_20_04/python:python-kaitaistruct.svg[package info for Ubuntu]]
 
-* If your project is using *requirements.txt* to manage your
-  dependencies, add the following line to it:
+
+* Add the following dependency specifier into the package configuration
+of the packaging tool you use:
 +
 ----
 kaitaistruct
 ----
 +
-and then run `pip install -r requirements.txt` to update all your
-dependencies.
+and then run `python3 -m pip install --upgrade -e ./` in the dir with your project
+in order to install your package and all its dependencies in
+an editable way. If you don't want to package your software,
+but only install its dependencies, add `kaitaistruct` into `requirements.txt`.
 
-* Otherwise, you can just install the package manually using *pip*
+* Otherwise, you can just install the package manually using `pip`
   (Python package manager):
 +
 [source,shell]
-pip install kaitaistruct
+python3 -m pip install --upgrade kaitaistruct
 
 [[add-runtime-snapshot]]
 ==== Using latest (snapshot) version
 
-If you're using latest (unreleased AKA "unstable" AKA "snapshot") build
-of Kaitai Struct compiler, that will require latest runtime libraries as
-well:
+If you're using latest (unreleased AKA "bleeding edge" AKA "unstable"
+AKA "snapshot" AKA "nightly") build of Kaitai Struct compiler, that will
+require latest runtime libraries as well:
 
-* If your project is using *requirements.txt* to manage your
-  dependencies, add the following line to it:
+* You can a make `pip` to use a snapshot version of the runtime by
+  adding a https://www.python.org/dev/peps/pep-0508/[PEP 508]
+  dependency specifier into the config of your favorite build tool:
 +
 ----
 kaitaistruct @ git+https://github.com/kaitai-io/kaitai_struct_python_runtime.git
 ----
 +
-and then run `pip install -r requirements.txt` to update all your
-dependencies.
+.
 
 * Otherwise, you can just install the package manually using *pip*
   (Python package manager):
 +
 [source,shell]
-pip install --upgrade --pre git+https://github.com/kaitai-io/kaitai_struct_python_runtime.git
+python3 -m pip install --upgrade --pre git+https://github.com/kaitai-io/kaitai_struct_python_runtime.git
+
 
 [[add-dependencies]]
-=== Adding dependencies
+=== Adding dependencies manually
 
-<<ksy_reference#enums,Enums>> implementation in Python requires a enum
-support as described in
+<<ksy_reference#enums,Enums>> implementation in Python requires
+a enum support as described in
 https://www.python.org/dev/peps/pep-0435/[PEP-0435]. This support is
 available out of the box in standard libraries since Python v3.4, or
 since v2.4 using https://pypi.org/project/enum34/[enum34] PyPi
 compatibility layer.
 
-* On Debian / Ubuntu, this library can be installed with `sudo apt-get
-  install python-enum34`
-* Otherwise, one can use just `sudo pip install enum34`
+* One usually doesn't need to install this lib manually, `pip` will install it
+   automatically if it is needed.
+* One can also install it manually:
+** One can use just `python -m pip install enum34`. Don't do it on
+     later pythons or the apps using just `enum` will be broken!
+** On Debian / Ubuntu, this library can be installed with
+    `sudo apt-get install -y python-enum34`.
 
 [[automation]]
 === Automation of compilation process
@@ -113,30 +155,23 @@ https://setuptools.readthedocs.io/en/latest/[Setuptools] is the de-facto
 standard way of building and installing python packages. This library
 allows extension with
 https://setuptools.readthedocs.io/en/latest/setuptools.html#extending-and-reusing-setuptools[plugins].
-https://github.com/KOLANICH have developed
-https://github.com/kaitaiStructCompile/kaitaiStructCompile.py[an extension to
-setuptools], allowing you to automate compilation of `*.ksy` files as the
+https://gitlab.com/KOLANICH has developed
+https://gitlab.com/kaitaiStructCompile.py/kaitaiStructCompile.setuptools[an extension to setuptools], allowing you to automate compilation of `*.ksy` files as the
 part of python module build process. The library provides a mostly
-declarative syntax to facilitate installation: you add a parameter
-`kaitai` to your `setup.py` where you enumerate files that you want
-compiled, output directory, compilation flags, and source code
-post-compilation transformations. Here are some examples:
-https://github.com/KOLANICH/NTMDTRead/blob/master/setup.py[1],
-https://github.com/KOLANICH/SpecprParser.py/blob/master/setup.py[2].
+declarative syntax to facilitate installation: you add a section
+`[tool.kaitai]` to your `pyproject.toml` where you enumerate the files that you want
+compiled, output directory, compilation flags, source code. 
+Post-compilation transformations are currently supported only via legacy syntax via `setup.py`. The links to examples can be found in the project docs.
 
 Here are
-https://github.com/KOLANICH/kaitaiStructCompile.py/blob/master/kaitaiStructCompile/config.schema.json[the
-docs] in JSON Schema format.
+https://gitlab.com/kaitaiStructCompile.py/kaitaiStructCompile.schemas/blob/master/kaitaiStructCompile/schemas/schemas/config.schema.json[the docs] in https://json-schema.org/specification.html[JSON Schema] format.
 
-Please remember that this lib is VERY UNSTABLE and very likely to be
-improved in a way that changes API (but due to API simplicity it'd be
+Please remember that this lib is **very unstable** and very likely to be
+improved in a way that changes its API (but due to the API simplicity it'd be
 easy to fix your code), but I guess it's much better to use this than to
 reinvent the wheel.
-https://github.com/kaitaiStructCompile/kaitaiStructCompile.py/issues[Contributions
-are welcome!]
-
-Please note that this lib is NOT available on
-https://pypi.org/[pypi] and if you want to install it
-automatically, you should add
-`git+https://github.com/KOLANICH/kaitaiStructCompile.py` into
-`dependency_links` in the config passed to `setuptools.setup`.
+https://gitlab.com/kaitaiStructCompile.py/kaitaiStructCompile.py/issues[Contributions are welcome!]
+
+Please note that this lib is NOT available on https://pypi.python.org[pypi]
+and should be installed manually, since currently `build_system` of
+`pyproject.toml` doesn't support PEP 508 specifiers.