python: add a pycodestyle test

Look for pycodestyle, and use it to check all the Python sources (tests
and auxiliary scripts included) of the Python bindings.

config.sh.in

@@ -20,3 +20,4 @@
 # mostly used in other shell scripts.
 
 export XMLLINT="@XMLLINT@"
+export PYCODESTYLE="@PYCODESTYLE@"

m4/guestfs-python.m4

@@ -86,6 +86,9 @@ AS_IF([test "x$enable_python" != "xno"],[
             PYTHON_EXT_SUFFIX=$python_ext_suffix
         fi
         AC_MSG_RESULT([$PYTHON_EXT_SUFFIX])
+
+        AC_CHECK_PROGS([PYCODESTYLE],[pycodestyle],[no])
+        AM_CONDITIONAL([HAVE_PYCODESTYLE], [test "x$PYCODESTYLE" != "xno"])
     fi
 
     AC_SUBST(PYTHON_PREFIX)

python/Makefile.am

@@ -38,6 +38,7 @@ EXTRA_DIST = \
 	setup.py.in \
 	run-bindtests \
 	run-python-tests \
+	test-pycodestyle.sh \
 	t/__init__.py \
 	t/README \
 	t/test[0-9]*.py
@@ -121,6 +122,10 @@ if ENABLE_APPLIANCE
 TESTS += run-python-tests
 endif ENABLE_APPLIANCE
 
+if HAVE_PYCODESTYLE
+TESTS += test-pycodestyle.sh
+endif
+
 endif HAVE_PYTHON
 
 # Extra clean.

python/test-pycodestyle.sh

@@ -0,0 +1,28 @@
+#!/bin/bash -
+# libguestfs
+# Copyright (C) 2020 Red Hat Inc.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+
+set -e
+
+$TEST_FUNCTIONS
+skip_if_skipped
+
+# Gather the list of Python sources.
+# (-u is passed to to sort to avoid duplicates in case builddir==srcdir)
+files="$(find "$srcdir" . -name '*.py' | sort -u)"
+
+$PYCODESTYLE $files