[python] - issue #1172 - provide switching versions using update-alternatives (#1260)

* [python] - issue #1172 - add version switching mechanism using update-alternatives

* removed commented code

* [python] - update-alternatives addition for ease in switching of python versions - complete

* changes for passing of other tests !!

* change for better positioning of code

* Added test case scenario for Update-Alternatives check

* added scenario for testing

* [alternatives] - added option for fedora, centos & rhel

* changed file name

* changes for update-alternatives test case proper functioning

* arrange in asc order for default value retention after testing ends

src/python/install.sh

@@ -766,15 +766,19 @@ esac
 
 check_packages ${REQUIRED_PKGS}
 
+# Function to get the major version from a SemVer string
+get_major_version() {
+    local version="$1"
+    echo "$version" | cut -d '.' -f 1
+}
+
 # Install Python from source if needed
 if [ "${PYTHON_VERSION}" != "none" ]; then
     if ! cat /etc/group | grep -e "^python:" > /dev/null 2>&1; then
         groupadd -r python
     fi
     usermod -a -G python "${USERNAME}"
-
     CURRENT_PATH="${PYTHON_INSTALL_PATH}/current"
-
     install_python ${PYTHON_VERSION}
 
     # Additional python versions to be installed but not be set as default.
@@ -783,9 +787,27 @@ if [ "${PYTHON_VERSION}" != "none" ]; then
         OLDIFS=$IFS
         IFS=","
             read -a additional_versions <<< "$ADDITIONAL_VERSIONS"
-            for version in "${additional_versions[@]}"; do
+            major_version=$(get_major_version ${VERSION})
+            if type apt-get > /dev/null 2>&1; then
+                # Debian/Ubuntu: Use update-alternatives
+                update-alternatives --install ${CURRENT_PATH} python${major_version} ${PYTHON_INSTALL_PATH}/${VERSION} $((${#additional_versions[@]}+1))
+                update-alternatives --set python${major_version} ${PYTHON_INSTALL_PATH}/${VERSION}
+            elif type dnf > /dev/null 2>&1 || type yum > /dev/null 2>&1 || type microdnf > /dev/null 2>&1; then
+                # Fedora/RHEL/CentOS: Use alternatives
+                alternatives --install ${CURRENT_PATH} python${major_version} ${PYTHON_INSTALL_PATH}/${VERSION} $((${#additional_versions[@]}+1))
+                alternatives --set python${major_version} ${PYTHON_INSTALL_PATH}/${VERSION}
+            fi
+            for i in "${!additional_versions[@]}"; do
+                version=${additional_versions[$i]}
                 OVERRIDE_DEFAULT_VERSION="false"
                 install_python $version
+                if type apt-get > /dev/null 2>&1; then
+                    # Debian/Ubuntu: Use update-alternatives
+                    update-alternatives --install ${CURRENT_PATH} python${major_version} ${PYTHON_INSTALL_PATH}/${VERSION} $((${i}+1))
+                elif type dnf > /dev/null 2>&1 || type yum > /dev/null 2>&1 || type microdnf > /dev/null 2>&1; then
+                    # Fedora/RHEL/CentOS: Use alternatives
+                    alternatives --install ${CURRENT_PATH} python${major_version} ${PYTHON_INSTALL_PATH}/${VERSION} $((${i}+1))
+                fi
             done
         INSTALL_PATH="${OLD_INSTALL_PATH}"
         IFS=$OLDIFS

test/python/alternatives_switchable_versions.sh

+#!/bin/bash
+
+set -e
+
+# Optional: Import test library
+source dev-container-features-test-lib
+
+check "python version 3.11 installed as default" bash -c "python --version | grep 3.11"
+check "python3 version 3.11 installed as default" bash -c "python3 --version | grep 3.11"
+check "python version 3.10.5 installed"  bash -c "ls -l /usr/local/python | grep 3.10.5"
+check "python version 3.8 installed"  bash -c "ls -l /usr/local/python | grep 3.8"
+check "python version 3.9.13 installed"  bash -c  "ls -l /usr/local/python | grep 3.9.13"
+
+# Check paths in settings
+check "current symlink is correct" bash -c "which python | grep /usr/local/python/current/bin/python"
+check "current symlink works" /usr/local/python/current/bin/python --version
+
+# check alternatives command
+check_version_switch() {
+    if type apt-get > /dev/null 2>&1; then
+        PYTHON_ALTERNATIVES=$(update-alternatives --query python3 | grep -E 'Alternative:|Priority:')
+        STYLE="debian"
+    elif type dnf > /dev/null 2>&1 || type yum > /dev/null 2>&1 || type microdnf > /dev/null 2>&1; then
+        PYTHON_ALTERNATIVES=$(alternatives --display python3 | grep " - priority")
+        STYLE="fedora"
+    else
+        echo "No supported package manager found."
+        exit 1
+    fi
+
+    AVAILABLE_VERSIONS=()
+    INDEX=1
+    echo "Available Python versions:"
+    if [ "${STYLE}" = "debian" ]; then
+        while read -r alt && read -r pri; do
+            PATH=${alt#Alternative: }   # Extract only the path
+            PRIORITY=${pri#Priority: }  # Extract only the priority number
+            TEMP_VERSIONS+=("${PRIORITY} ${PATH}")
+            echo "$INDEX) $PATH (Priority: $PRIORITY)"
+            ((INDEX++))
+        done <<< "${PYTHON_ALTERNATIVES}"
+    elif [ "${STYLE}" = "fedora" ]; then
+        export PATH="/usr/bin:$PATH"
+        # Fedora/RHEL output: one line per alternative in the format:
+        while IFS= read -r line; do
+            # Split using " - priority " as a delimiter.
+            PATH=$(/usr/bin/awk -F' - priority ' '{print $1}' <<< "$line" | /usr/bin/xargs /bin/echo)
+            PRIORITY=$(/usr/bin/awk -F' - priority ' '{print $2}' <<< "$line" | /usr/bin/xargs /bin/echo)    
+            TEMP_VERSIONS+=("${PRIORITY} ${PATH}") 
+            echo "$INDEX) $PATH (Priority: $PRIORITY_VALUE)"
+            ((INDEX++))
+        done <<< "${PYTHON_ALTERNATIVES}"
+    fi
+
+    export PATH="/usr/bin:$PATH"
+    # Sort by priority (numerically ascending)
+    IFS=$'\n' TEMP_VERSIONS=($(sort -n <<<"${TEMP_VERSIONS[*]}"))
+    unset IFS
+
+    # Populate AVAILABLE_VERSIONS from sorted data
+    AVAILABLE_VERSIONS=()
+    INDEX=1
+    echo -e "\nAvailable Python versions (Sorted in asc order of priority):"
+    for ENTRY in "${TEMP_VERSIONS[@]}"; do
+        PRIORITY=${ENTRY%% *}  # Extract priority (first part before space)
+        PATH=${ENTRY#* }       # Extract path (everything after first space)
+        AVAILABLE_VERSIONS+=("${PATH}")
+        echo "$INDEX) $PATH (Priority: $PRIORITY)"
+        ((INDEX++))
+    done
+
+    echo -e "\nAvailable Versions Count: ${#AVAILABLE_VERSIONS[@]}"
+    # Ensure at least 4 alternatives exist
+    if [ "${#AVAILABLE_VERSIONS[@]}" -lt 4 ]; then
+        echo "Error: Less than 4 Python versions registered in update-alternatives."
+        exit 1
+    fi
+    
+    export PATH="/usr/bin:$PATH"
+    echo -e "\nSwitching to different versions using update-alternatives --set command...\n"
+    for CHOICE in {1..4}; do
+        SELECTED_VERSION="${AVAILABLE_VERSIONS[$((CHOICE - 1))]}"
+        echo "Switching to: ${SELECTED_VERSION}"
+        if command -v apt-get > /dev/null 2>&1; then
+            /usr/bin/update-alternatives --set python3 ${SELECTED_VERSION}
+        elif command -v dnf > /dev/null 2>&1 || command -v yum > /dev/null 2>&1 || command -v microdnf > /dev/null 2>&1; then
+            /usr/sbin/alternatives --set python3 ${SELECTED_VERSION}
+        fi
+        # Verify the switch
+        echo "Python version after switch:"
+        /usr/local/python/current/bin/python3 --version
+        /bin/sleep 1
+        echo -e "\n"
+    done
+    echo -e "Update-Alternatives --display: \n"
+    if type apt-get > /dev/null 2>&1; then
+        /usr/bin/update-alternatives --display python3
+    elif type dnf > /dev/null 2>&1 || type yum > /dev/null 2>&1 || type microdnf > /dev/null 2>&1; then
+        /usr/sbin/alternatives --display python3
+    fi
+}
+
+check "Version Switch With Update_Alternatives" check_version_switch
\ No newline at end of file

test/python/scenarios.json

@@ -255,5 +255,25 @@
                 "enableShared": true
             }
         }
+    },
+    "update_alternatives_switchable_versions": {
+        "image": "ubuntu:focal",
+        "features": {
+            "python": {
+                "version": "3.11",
+                "installTools": true,
+                "additionalVersions": "3.8,3.9.13,3.10.5"
+            }
+        }
+    },
+    "alternatives_switchable_versions": {
+        "image": "fedora",
+        "features": {
+            "python": {
+                "version": "3.11",
+                "installTools": true,
+                "additionalVersions": "3.8,3.9.13,3.10.5"
+            }
+        }
     }
 }
\ No newline at end of file

test/python/update_alternatives_switchable_versions.sh

+#!/bin/bash
+
+set -e
+
+# Optional: Import test library
+source dev-container-features-test-lib
+
+check "python version 3.11 installed as default" bash -c "python --version | grep 3.11"
+check "python3 version 3.11 installed as default" bash -c "python3 --version | grep 3.11"
+check "python version 3.10.5 installed"  bash -c "ls -l /usr/local/python | grep 3.10.5"
+check "python version 3.8 installed"  bash -c "ls -l /usr/local/python | grep 3.8"
+check "python version 3.9.13 installed"  bash -c  "ls -l /usr/local/python | grep 3.9.13"
+
+# Check paths in settings
+check "current symlink is correct" bash -c "which python | grep /usr/local/python/current/bin/python"
+check "current symlink works" /usr/local/python/current/bin/python --version
+
+# check alternatives command
+check_version_switch() {
+    if type apt-get > /dev/null 2>&1; then
+        PYTHON_ALTERNATIVES=$(update-alternatives --query python3 | grep -E 'Alternative:|Priority:')
+        STYLE="debian"
+    elif type dnf > /dev/null 2>&1 || type yum > /dev/null 2>&1 || type microdnf > /dev/null 2>&1; then
+        PYTHON_ALTERNATIVES=$(alternatives --display python3 | grep " - priority")
+        STYLE="fedora"
+    else
+        echo "No supported package manager found."
+        exit 1
+    fi
+    AVAILABLE_VERSIONS=()
+    INDEX=1
+    echo "Available Python versions:"
+    if [ "${STYLE}" = "debian" ]; then
+        while read -r alt && read -r pri; do
+            PATH=${alt#Alternative: }   # Extract only the path
+            PRIORITY=${pri#Priority: }  # Extract only the priority number
+            TEMP_VERSIONS+=("${PRIORITY} ${PATH}")
+            echo "$INDEX) $PATH (Priority: $PRIORITY)"
+            ((INDEX++))
+        done <<< "${PYTHON_ALTERNATIVES}"
+    elif [ "${STYLE}" = "fedora" ]; then
+        export PATH="/usr/bin:$PATH"
+        # Fedora/RHEL output: one line per alternative in the format:
+        while IFS= read -r line; do
+            # Split using " - priority " as a delimiter.
+            PATH=$(/usr/bin/awk -F' - priority ' '{print $1}' <<< "$line" | /usr/bin/xargs /bin/echo)
+            PRIORITY=$(/usr/bin/awk -F' - priority ' '{print $2}' <<< "$line" | /usr/bin/xargs /bin/echo)    
+            TEMP_VERSIONS+=("${PRIORITY} ${PATH}") 
+            echo "$INDEX) $PATH (Priority: $PRIORITY_VALUE)"
+            ((INDEX++))
+        done <<< "${PYTHON_ALTERNATIVES}"
+    fi
+
+    export PATH="/usr/bin:$PATH"   
+    # Sort by priority (numerically ascending)
+    IFS=$'\n' TEMP_VERSIONS=($(sort -n <<<"${TEMP_VERSIONS[*]}"))
+    unset IFS
+
+    # Populate AVAILABLE_VERSIONS from sorted data
+    AVAILABLE_VERSIONS=()
+    INDEX=1
+    echo -e "\nAvailable Python versions (Sorted in asc order of priority):"
+    for ENTRY in "${TEMP_VERSIONS[@]}"; do
+        PRIORITY=${ENTRY%% *}  # Extract priority (first part before space)
+        PATH=${ENTRY#* }       # Extract path (everything after first space)
+        AVAILABLE_VERSIONS+=("${PATH}")
+        echo "$INDEX) $PATH (Priority: $PRIORITY)"
+        ((INDEX++))
+    done
+
+    echo -e "\nAvailable Versions Count: ${#AVAILABLE_VERSIONS[@]}\n"
+    # Ensure at least 4 alternatives exist
+    if [ "${#AVAILABLE_VERSIONS[@]}" -lt 4 ]; then
+        echo "Error: Less than 4 Python versions registered in update-alternatives."
+        exit 1
+    fi
+
+    export PATH="/usr/bin:$PATH"
+    echo -e "\nSwitching to different versions using update-alternatives --set command...\n"
+    for CHOICE in {1..4}; do
+        SELECTED_VERSION="${AVAILABLE_VERSIONS[$((CHOICE - 1))]}"
+        echo "Switching to: ${SELECTED_VERSION}"
+        if command -v apt-get > /dev/null 2>&1; then
+            /usr/bin/update-alternatives --set python3 ${SELECTED_VERSION}
+        elif command -v dnf > /dev/null 2>&1 || command -v yum > /dev/null 2>&1 || command -v microdnf > /dev/null 2>&1; then
+            /usr/sbin/alternatives --set python3 ${SELECTED_VERSION}
+        fi
+        # Verify the switch
+        echo "Python version after switch:"
+        /usr/local/python/current/bin/python3 --version
+        /bin/sleep 1
+        echo -e "\n"
+    done
+    echo -e "Update-Alternatives --display: \n"
+    if type apt-get > /dev/null 2>&1; then
+        /usr/bin/update-alternatives --display python3
+    elif type dnf > /dev/null 2>&1 || type yum > /dev/null 2>&1 || type microdnf > /dev/null 2>&1; then
+        /usr/sbin/alternatives --display python3
+    fi
+}
+
+check "Version Switch With Update_Alternatives" check_version_switch
\ No newline at end of file