Add chapter "Working with Python"

Author: sinoroc

src/python/index.rst

@@ -17,6 +17,7 @@ Python
     pex
     setuptools
     chameleon
+    working
 
 
 .. EOF

src/python/working.rst

@@ -0,0 +1,84 @@
+..
+
+
+Working with Python
+===================
+
+No *pip*
+--------
+
+Do not install a global system-wide version of *pip* at all.
+
+There is almost never a good reason to install global system-wide packages via
+*pip* to begin with. Especially on Linux where the default version of Python
+is part of the system and used by the system. So mixing this with Python
+projects that the user install install themselves via *pip* is very likely to
+cause conflicts sooner rather than later.
+
+
+Use isolation
+-------------
+
+If Python tools are needed to be always available from the command line, then
+isolate them with *zapp*, *shiv*, or *pex*.
+
+* *zapp* https://pypi.org/project/zapp/
+* *shiv* https://pypi.org/project/shiv/
+* *pex* https://pypi.org/project/pex/
+
+Those are all *zipapp* single-file Python executables.
+
+* https://www.python.org/dev/peps/pep-0441/
+* https://docs.python.org/3/library/zipapp.html
+
+*shiv* and *pex* applications are self extractable. *zapp* does not need to be
+extracted. The code is executed directly from within the zip-compressed
+archive.
+
+*pex* applications are executed from their own virtual environment. *zapp*
+applications are not executed in a virtual environment. Not sure about *shiv*.
+
+*shiv* applications show up somehow in the current environment. Whereas *zapp*
+applications do not, so they are perfect for tools such as *deptree*, and
+*pipdeptree*.
+
+
+Use *toolmaker*
+---------------
+
+To automate the creation of single file Python applications with *zapp*,
+*shiv*, or *pex*, one can use *toolmaker*.
+
+* https://pypi.org/project/toolmaker/
+
+
+Use *venv*
+----------
+
+Python 3 has the module *venv* in its standard library since version 3.3.
+
+* https://docs.python.org/3/library/venv.html
+
+So the need for the third party library *virtualenv* is much less pressing.
+
+.. code::
+
+    $ python3 -m venv .venv
+    $ . .venv/bin/activate
+
+
+Do not activate virtual environments
+------------------------------------
+
+The scripts that are installed in a virtual environment (with *setuptools* at
+least) get a shebang with the full path to the Python interpeter from the
+virtual environment. So there is no need to activate the virtual environment
+to call such scripts.
+
+.. code::
+
+    $ .venv/bin/myscript
+    $ .venv/bin/python3 -m mymodule
+
+
+.. EOF