[build] dependency-check: that python2.7 and python3 exist and 2.7 is default (#1876)

Author: psmit

tools/extras/check_dependencies.sh

@@ -87,28 +87,44 @@ if ! which awk >&/dev/null; then
  add_packages gawk gawk gawk
 fi
 
-if which python >&/dev/null ; then
+pythonok=true
+if ! which python2.7 >&/dev/null; then
+ echo "$0: python2.7 is not installed"
+ add_packages python2.7
+ pythonok=false
+fi
+
+if ! which python3 >&/dev/null; then
+ echo "$0: python3 is not installed"
+ add_packages python3
+ pythonok=false
+fi
+
+( 
+#Use a subshell so that sourcing env.sh does not have an influence on the rest of the script
+[ -f ./env.sh ] && . ./env.sh
+if $pythonok && ! which python2 >&/dev/null; then
+ mkdir -p $PWD/python
+ echo "$0: python2.7 is installed, but the python2 binary does not exist. Creating a symlink and adding this to tools/env.sh"
+ ln -s $(which python2.7) $PWD/python/python2
+ echo "export PATH=$PWD/python:\${PATH}" >> env.sh
+fi
+
+if [[ -f $PWD/python/.use_default_python && -f $PWD/python/python ]]; then
+ rm $PWD/python/python 
+fi
+
+if $pythonok && which python >&/dev/null && [[ ! -f $PWD/python/.use_default_python ]]; then
  version=`python 2>&1 --version | awk '{print $2}' `
  if [[ $version != "2.7"* ]] ; then
- if which python2.7 >&/dev/null || which python2 >&/dev/null ; then
- echo "$0: python 2.7 is not the default python. You should either make it"
- echo "$0: default or create an bash alias for kaldi scripts to run correctly"
- status=1
- else
- echo "$0: python 2.7 is not installed"
- add_packages python2.7 python python2.7
- fi
- fi
-else
- if which python2.7 >&/dev/null || which python2 >&/dev/null ; then
- echo "$0: python 2.7 is not the default python. You should either make it"
- echo "$0: default or create an bash alias for kaldi scripts to run correctly"
- status=1
- else
- echo "$0: python is not installed (we need python 2.7)"
- add_packages python2.7 python python2.7
+ echo "$0: WARNING python 2.7 is not the default python. We fixed this by adding a correct symlink more prominently on the path."
+ echo "$0: If you really want to use python $version as default, add an empty file $PWD/python/.use_default_python and run this script again." 
+ mkdir -p $PWD/python
+ ln -s $(which python2.7) $PWD/python/python
+ echo "export PATH=$PWD/python:\${PATH}" >> env.sh
  fi
 fi
+)
 
 printed=false