Add Travis check for unused Python imports

.travis.yml

@@ -21,7 +21,7 @@ env:
     - WINEDEBUG=fixme-all
   matrix:
 # ARM
-    - HOST=arm-linux-gnueabihf PACKAGES="g++-arm-linux-gnueabihf" DEP_OPTS="NO_QT=1" CHECK_DOC=1 GOAL="install" BITCOIN_CONFIG="--enable-glibc-back-compat --enable-reduce-exports"
+    - HOST=arm-linux-gnueabihf PACKAGES="g++-arm-linux-gnueabihf python3-pip" DEP_OPTS="NO_QT=1" CHECK_DOC=1 GOAL="install" BITCOIN_CONFIG="--enable-glibc-back-compat --enable-reduce-exports"
 # Win32
     - HOST=i686-w64-mingw32 DPKG_ADD_ARCH="i386" DEP_OPTS="NO_QT=1" PACKAGES="python3 nsis g++-mingw-w64-i686 wine1.6" RUN_TESTS=true GOAL="install" BITCOIN_CONFIG="--enable-reduce-exports"
 # Qt4 & system libs
@@ -43,6 +43,7 @@ install:
     - if [ -n "$DPKG_ADD_ARCH" ]; then sudo dpkg --add-architecture "$DPKG_ADD_ARCH" ; fi
     - if [ -n "$PACKAGES" ]; then travis_retry sudo apt-get update; fi
     - if [ -n "$PACKAGES" ]; then travis_retry sudo apt-get install --no-install-recommends --no-upgrade -qq $PACKAGES; fi
+    - if [ "$CHECK_DOC" = 1 -a "$TRAVIS_EVENT_TYPE" = "pull_request" ]; then travis_retry pip3 install flake8 --user; fi
 before_script:
     - if [ "$CHECK_DOC" = 1 -a "$TRAVIS_EVENT_TYPE" = "pull_request" ]; then contrib/devtools/commit-script-check.sh $TRAVIS_COMMIT_RANGE; fi
     - if [ "$CHECK_DOC" = 1 ]; then contrib/devtools/git-subtree-check.sh src/crypto/ctaes; fi

contrib/devtools/lint-python.sh

@@ -0,0 +1,10 @@
+#!/bin/sh
+#
+# Copyright (c) 2017 The Bitcoin Core developers
+# Distributed under the MIT software license, see the accompanying
+# file COPYING or http://www.opensource.org/licenses/mit-license.php.
+#
+# Check for specified flake8 warnings in python files.
+
+# F401: module imported but unused
+flake8 --ignore=B,C,E,F,I,N,W --select=F401 .