Merge #11835: Add Travis check for unused Python imports

d60b32074 Add Travis check for unused Python imports (practicalswift)
c7399e708 Remove unused Python imports (practicalswift)

Pull request description:

  Add Travis check for unused Python imports.

  ```
  $ contrib/devtools/lint-python.sh
  ./test/functional/example_test.py:18:1: F401 'test_framework.mininode.NODE_NETWORK' imported but unused
  ./test/functional/test_framework/messages.py:27:1: F401 'test_framework.util.wait_until' imported but unused
  ./test/functional/test_framework/test_framework.py:16:1: F401 'traceback' imported but unused
  ```

Tree-SHA512: 78e50fb1488abe3ebe365e766cb8d6d448cf1bd16c8691e102cb9bf7c202988bdf6e10b25ff772c62e05c72568168462e88cdc7ad98069d9eb3be727735b2d56

5 files changed, 13 insertions, 4 deletions

diff --git a/.travis.yml b/.travis.yml
index d3dd37e76c..ab002acc53 100644
--- a/.travis.yml
+++ b/.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
diff --git a/contrib/devtools/lint-python.sh b/contrib/devtools/lint-python.sh
new file mode 100755
index 0000000000..9303fcc8ef
--- /dev/null
+++ b/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 .
diff --git a/test/functional/example_test.py b/test/functional/example_test.py
index 289fa248e0..35a6bd2673 100755
--- a/test/functional/example_test.py
+++ b/test/functional/example_test.py
@@ -22,7 +22,6 @@ from test_framework.mininode import (
     mininode_lock,
     msg_block,
     msg_getdata,
-    NODE_NETWORK,
 )
 from test_framework.test_framework import BitcoinTestFramework
 from test_framework.util import (
diff --git a/test/functional/test_framework/messages.py b/test/functional/test_framework/messages.py
index eee24910cb..2ab1bdac0f 100644
--- a/test/functional/test_framework/messages.py
+++ b/test/functional/test_framework/messages.py
@@ -24,7 +24,7 @@ import struct
 import time
 
 from test_framework.siphash import siphash256
-from test_framework.util import hex_str_to_bytes, bytes_to_hex_str, wait_until
+from test_framework.util import hex_str_to_bytes, bytes_to_hex_str
 
 MIN_VERSION_SUPPORTED = 60001
 MY_VERSION = 70014  # past bip-31 for ping/pong
diff --git a/test/functional/test_framework/test_framework.py b/test/functional/test_framework/test_framework.py
index 54fe689686..a46312d62c 100755
--- a/test/functional/test_framework/test_framework.py
+++ b/test/functional/test_framework/test_framework.py
@@ -13,7 +13,6 @@ import shutil
 import sys
 import tempfile
 import time
-import traceback
 
 from .authproxy import JSONRPCException
 from . import coverage