Add Python 3.7.0b4

Author: lelit

README.rst

@@ -58,7 +58,7 @@ directory for source code.
 
 The images currently contain:
 
-- CPython 2.7, 3.3, 3.4, 3.5 and 3.6, installed in
+- CPython 2.7, 3.3, 3.4, 3.5, 3.6 and 3.7, installed in
   ``/opt/python/<python tag>-<abi tag>``. The directories are named
   after the PEP 425 tags for each environment --
   e.g. ``/opt/python/cp27-cp27mu`` contains a wide-unicode CPython 2.7

docker/build_scripts/build_env.sh

@@ -1,7 +1,7 @@
 # source me
 
 PYTHON_DOWNLOAD_URL=https://www.python.org/ftp/python
-CPYTHON_VERSIONS="2.7.14 3.4.8 3.5.5 3.6.5"
+CPYTHON_VERSIONS="2.7.14 3.4.8 3.5.5 3.6.5 3.7.0b4"
 
 # openssl version to build, with expected sha256 hash of .tar.gz
 # archive.

docker/build_scripts/build_utils.sh

@@ -19,6 +19,15 @@ function lex_pyver {
 }
 
 
+function pyver_dist_dir {
+    # Echoes the dist directory name of given pyver, removing alpha/beta prerelease
+    # Thus:
+    # 3.2.1   -> 3.2.1
+    # 3.7.0b4 -> 3.7.0
+    echo $1 | awk -F "." '{printf "%d.%d.%d", $1, $2, $3}'
+}
+
+
 function do_cpython_build {
     local py_ver=$1
     check_var $py_ver
@@ -64,8 +73,9 @@ function build_cpython {
     local py_ver=$1
     check_var $py_ver
     check_var $PYTHON_DOWNLOAD_URL
-    curl -fsSLO $PYTHON_DOWNLOAD_URL/$py_ver/Python-$py_ver.tgz
-    curl -fsSLO $PYTHON_DOWNLOAD_URL/$py_ver/Python-$py_ver.tgz.asc
+    local py_dist_dir=$(pyver_dist_dir $py_ver)
+    curl -fsSLO $PYTHON_DOWNLOAD_URL/$py_dist_dir/Python-$py_ver.tgz
+    curl -fsSLO $PYTHON_DOWNLOAD_URL/$py_dist_dir/Python-$py_ver.tgz.asc
     gpg --verify Python-$py_ver.tgz.asc
     if [ $(lex_pyver $py_ver) -lt $(lex_pyver 3.3) ]; then
         do_cpython_build $py_ver ucs2