POC: keep only cache for large, autogenerated files

This saves about 2 MiB from the package. When all rpms get extracted,
the comparison is as follows on an ext4 filesystem:

With this patch:
$ du -s usr
195828 usr/

Without this patch:
$ du -s usr
198224 usr/

Which is a difference of 2.396 MiB.

To reduce the filesystem footprint of the Python installation, some
files are now being removed and only one level of their pycache
(non-optimized) is being kept.

These particular files were chosen for their size and the fact that they
are autogenerated, thus hard to read.

python3.9.spec

@@ -17,7 +17,7 @@ URL: https://www.python.org/
 %global prerel b4
 %global upstream_version %{general_version}%{?prerel}
 Version: %{general_version}%{?prerel:~%{prerel}}
-Release: 1%{?dist}
+Release: 2%{?dist}
 License: Python
 
 
@@ -1014,6 +1014,13 @@ ln -s ./python3-debug %{buildroot}%{_bindir}/python-debug
 %endif
 %endif
 
+# Remove large, autogenerated sources and keep only the non-optimized pycache
+for file in %{buildroot}%{pylibdir}/pydoc_data/topics.py $(grep --include='*.py' -lr %{buildroot}%{pylibdir}/encodings -e 'Python Character Mapping Codec .* from .* with gencodec.py'); do
+    directory=$(dirname ${file})
+    module=$(basename ${file%%.py})
+    mv ${directory}/{__pycache__/${module}.cpython-%{pyshortver}.pyc,${module}.pyc}
+    rm ${directory}/{__pycache__/${module}.cpython-%{pyshortver}.opt-?.pyc,${module}.py}
+done
 
 # ======================================================
 # Checks for packaging issues
@@ -1595,6 +1602,9 @@ CheckPython optimized
 # ======================================================
 
 %changelog
+* Thu Jul 16 2020 Marcel Plch <mplch@redhat.com> - 3.9.0~b4-2
+- Remove large, autogenerated Python sources and redundant pycache levels to reduce filesystem footprint
+
 * Sat Jul 04 2020 Tomas Hrnciar <thrnciar@redhat.com> - 3.9.0~b4-1
 - Update to 3.9.0b4