Merge ~cjwatson/launchpad-mojo-specs:utils-check-python-version into launchpad-mojo-specs:master

[Colin Watson]

Re-exec scripts using Python 2 where necessary

wendigo (the devops management host for PS4.5) is old and lacks a number of Python 3 libraries that we use; however, when deploying to PS5, we need to run on Ubuntu 20.04 LTS, which lacks Python 2 versions of the same libraries. To escape this Catch-22, re-exec ourselves using Python 2 if we find ourselves on a system that's known to be too old to support the Python 3 libraries we need.

[Ioana Lasc (ilasc)]

review: Approve

diff --git a/lp-codeimport/update-code-asset b/lp-codeimport/update-code-asset
index fdc7fbf..e7386e3 100755
--- a/lp-codeimport/update-code-asset
+++ b/lp-codeimport/update-code-asset
@@ -1,4 +1,6 @@
-#! /usr/bin/python
+#! /usr/bin/python3
+
+import utils.check_version  # noqa: F401
 
 import os
 import subprocess
diff --git a/lp-codeimport/upgrade-charms b/lp-codeimport/upgrade-charms
index ef477c7..10bf64e 100755
--- a/lp-codeimport/upgrade-charms
+++ b/lp-codeimport/upgrade-charms
@@ -1,4 +1,6 @@
-#! /usr/bin/python
+#! /usr/bin/python3
+
+import utils.check_version  # noqa: F401
 
 import os.path
 import subprocess
diff --git a/mojo-lp-git/run-payload-tests b/mojo-lp-git/run-payload-tests
index 8d9e5eb..7e61ac4 100755
--- a/mojo-lp-git/run-payload-tests
+++ b/mojo-lp-git/run-payload-tests
@@ -1,4 +1,6 @@
-#! /usr/bin/python
+#! /usr/bin/python3
+
+import utils.check_version  # noqa: F401
 
 import os
 import subprocess
diff --git a/mojo-lp-git/update-code-asset b/mojo-lp-git/update-code-asset
index bfc3c23..12492d9 100755
--- a/mojo-lp-git/update-code-asset
+++ b/mojo-lp-git/update-code-asset
@@ -1,4 +1,6 @@
-#! /usr/bin/python
+#! /usr/bin/python3
+
+import utils.check_version  # noqa: F401
 
 import os
 import subprocess
diff --git a/mojo-lp-git/upgrade-charms b/mojo-lp-git/upgrade-charms
index f215db1..4f5d386 100755
--- a/mojo-lp-git/upgrade-charms
+++ b/mojo-lp-git/upgrade-charms
@@ -1,4 +1,6 @@
-#! /usr/bin/python
+#! /usr/bin/python3
+
+import utils.check_version  # noqa: F401
 
 import os.path
 import subprocess
diff --git a/mojo-lp-signing/update-code-asset b/mojo-lp-signing/update-code-asset
index b140f51..aebf69b 100755
--- a/mojo-lp-signing/update-code-asset
+++ b/mojo-lp-signing/update-code-asset
@@ -1,4 +1,6 @@
-#! /usr/bin/python
+#! /usr/bin/python3
+
+import utils.check_version  # noqa: F401
 
 import os
 import subprocess
diff --git a/mojo-lp-signing/upgrade-charms b/mojo-lp-signing/upgrade-charms
index 9c69500..aa339ee 100755
--- a/mojo-lp-signing/upgrade-charms
+++ b/mojo-lp-signing/upgrade-charms
@@ -1,4 +1,6 @@
-#! /usr/bin/python
+#! /usr/bin/python3
+
+import utils.check_version  # noqa: F401
 
 import os.path
 import subprocess
diff --git a/utils/add-floating-ip b/utils/add-floating-ip
index 4540b3f..2024af6 100755
--- a/utils/add-floating-ip
+++ b/utils/add-floating-ip
@@ -1,10 +1,12 @@
-#!/usr/bin/python
+#!/usr/bin/python3
 #
 # Authors:      Paul Gear, Neale Pickett
 # Description:  Manage floating IP allocations in mojo local directory for a juju service or unit.
 # NOTE:         $MOJO_PROJECT and $MOJO_STAGE must be set before calling this script.
 #
 
+import check_version  # noqa: F401
+
 import json
 import os
 import subprocess
diff --git a/utils/check_version.py b/utils/check_version.py
 new file mode 100644
index 0000000..acf82ea
--- /dev/null
+++ b/utils/check_version.py
@@ -0,0 +1,17 @@
+# At the time of writing (June 2021), we still need to deploy code to PS4.5.
+# The devops management host for that cloud runs Ubuntu 14.04, which has
+# Python 3.4, and which also doesn't have many of the libraries we need
+# packaged for Python 3.  This abominable hack checks whether we're on 3.4,
+# and if so re-execs itself using Python 2.
+#
+# The Python version itself isn't really the important factor here, but it's
+# a proxy indicator that we can check easily.
+#
+# We should drop this as soon as we no longer need to support deploying from
+# Ubuntu 14.04.
+
+import os
+import sys
+
+if sys.version_info[0] == 3 and sys.version_info[1] < 5:
+    os.execv('/usr/bin/python2', [sys.argv[0]] + sys.argv)
diff --git a/utils/custom-secgroups.py b/utils/custom-secgroups.py
index af4eab5..f4e1059 100755
--- a/utils/custom-secgroups.py
+++ b/utils/custom-secgroups.py
@@ -1,9 +1,11 @@
-#! /usr/bin/python
+#! /usr/bin/python3
 # By wgrant, with some neutron manipulation stolen from cjwatson's
 # clean-up-secgroups.py.
 
 from __future__ import print_function
 
+import check_version  # noqa: F401
+
 __metaclass__ = type
 
 import argparse
diff --git a/utils/get-last-build-label b/utils/get-last-build-label
index fa26837..a12e797 100755
--- a/utils/get-last-build-label
+++ b/utils/get-last-build-label
@@ -1,4 +1,4 @@
-#! /usr/bin/python
+#! /usr/bin/python3
 
 """Print the last build label in a particular state.
 
@@ -8,6 +8,8 @@ shell.
 
 from __future__ import print_function
 
+import check_version  # noqa: F401
+
 import os
 
 import utils
diff --git a/utils/get-swift-storage-url b/utils/get-swift-storage-url
index 3119867..e34a597 100755
--- a/utils/get-swift-storage-url
+++ b/utils/get-swift-storage-url
@@ -1,9 +1,11 @@
-#! /usr/bin/python
+#! /usr/bin/python3
 
 """Print the Swift storage URL."""
 
 from __future__ import print_function
 
+import check_version  # noqa: F401
+
 import utils
 
 
diff --git a/utils/make-branches b/utils/make-branches
index f4ab582..c34bcb5 100755
--- a/utils/make-branches
+++ b/utils/make-branches
@@ -1,4 +1,6 @@
-#! /usr/bin/python
+#! /usr/bin/python3
+
+import check_version  # noqa: F401
 
 import os
 import shutil
diff --git a/utils/publish-build-assets b/utils/publish-build-assets
index 158bdc8..11ddd18 100755
--- a/utils/publish-build-assets
+++ b/utils/publish-build-assets
@@ -1,4 +1,6 @@
-#! /usr/bin/python
+#! /usr/bin/python3
+
+import check_version  # noqa: F401
 
 import os
 
diff --git a/utils/publish-last-build-label b/utils/publish-last-build-label
index 7bdf13c..0ff812b 100755
--- a/utils/publish-last-build-label
+++ b/utils/publish-last-build-label
@@ -1,8 +1,10 @@
-#! /usr/bin/python
+#! /usr/bin/python3
 
 """Publishes the last attempted build label to a specific swift file
 for use by other jobs which may trigger a spec run."""
 
+import check_version  # noqa: F401
+
 import os
 import shutil
 import tempfile
diff --git a/utils/set-local-config b/utils/set-local-config
index 21ab9e1..123059c 100755
--- a/utils/set-local-config
+++ b/utils/set-local-config
@@ -1,7 +1,9 @@
-#! /usr/bin/python
+#! /usr/bin/python3
 
 from __future__ import print_function
 
+import check_version  # noqa: F401
+
 import argparse
 import os.path
 
diff --git a/utils/set-service-options b/utils/set-service-options
index bb5c1e1..8b12678 100755
--- a/utils/set-service-options
+++ b/utils/set-service-options
@@ -1,7 +1,9 @@
-#! /usr/bin/python
+#! /usr/bin/python3
 
 from __future__ import print_function
 
+import check_version  # noqa: F401
+
 import base64
 import numbers
 import sys