Merge #14954: build: Require python 3.5

fa2797808e test: Remove python3.4 workaround in feature_dbcrash (MarcoFalke)
dddd1d05d3 .python-version: Specify full version 3.5.6 (MarcoFalke)
faa7cdf764 scripted-diff: Update copyright in ./test (MarcoFalke)
fa0e65b772 scripted-diff: test: Remove brackets after assert (MarcoFalke)
fab5a1e0f4 build: Require python 3.5 (MarcoFalke)
fa6bf21f5e scripted-diff: test: Use py3.5 bytes::hex() method (MarcoFalke)

Pull request description:

  Python 3.4 is EOL after March 2019, so switch to 3.5. See https://devguide.python.org/#status-of-python-branches

  This pull does the following in a bunch of commits:
  * scripted diff to use the `bytes::hex()` method in place of previous wrappers (`b2x`, `bytes_to_hex_str`, `hexlify`, ...)
  * Update the build system (gitian and travis) to remove python2.7 and replace it with python3.5
  * Another scripted-diff to remove brackets after `assert`. This is unrelated to the python3.5 switch, but a stylistic commit, so probably not worth to split up. The motivation behind it is to avoid asserting on data structures (such as tuples of length one), which never fails:
  ```py
  >>> assert(False,)   # with brackets
  >>> assert False,    # without brackets
  SyntaxError: invalid syntax
  >>> assert False     # proper assertion
  AssertionError
  ```
  * And then a final scripted diff to update the copyright headers in the `test` subfolder, since I touched most of the files anyway and it wouldn't make sense to split this commit out into a separate pull.

  For reference (contributed by luke-jr):

  Ubuntu LTS (bionic): 3.6.5
  Debian stable (stretch): 3.5.3
  RHEL 8 (expected before v0.19): 3.6.x
  Gentoo stable: 3.6.5
  Arch: 3.7.1

Tree-SHA512: 643c28cd2d5b9543ce4bf8ad2a8b282bc79b37dc5b25c9c8358e6ce201e2a67a546463e5f3430b16652eb2489d7c3ed4b0772cd2e2bf790fe68a5e3cc8a25029

8 files changed, 11 insertions, 102 deletions

diff --git a/contrib/devtools/README.md b/contrib/devtools/README.md
index 6ee65f40be..d66eff66be 100644
--- a/contrib/devtools/README.md
+++ b/contrib/devtools/README.md
@@ -167,7 +167,7 @@ still compatible with the minimum supported Linux distribution versions.
 
 Example usage after a gitian build:
 
-    find ../gitian-builder/build -type f -executable | xargs python contrib/devtools/symbol-check.py 
+    find ../gitian-builder/build -type f -executable | xargs python3 contrib/devtools/symbol-check.py
 
 If only supported symbols are used the return value will be 0 and the output will be empty.
 
diff --git a/contrib/devtools/symbol-check.py b/contrib/devtools/symbol-check.py
index c6158c9422..7729dd7257 100755
--- a/contrib/devtools/symbol-check.py
+++ b/contrib/devtools/symbol-check.py
@@ -9,7 +9,7 @@ still compatible with the minimum supported Linux distribution versions.
 
 Example usage:
 
-    find ../gitian-builder/build -type f -executable | xargs python contrib/devtools/symbol-check.py
+    find ../gitian-builder/build -type f -executable | xargs python3 contrib/devtools/symbol-check.py
 '''
 import subprocess
 import re
diff --git a/contrib/gitian-descriptors/gitian-linux.yml b/contrib/gitian-descriptors/gitian-linux.yml
index e97072c80a..1fc1ce98a9 100644
--- a/contrib/gitian-descriptors/gitian-linux.yml
+++ b/contrib/gitian-descriptors/gitian-linux.yml
@@ -30,7 +30,7 @@ packages:
 - "faketime"
 - "bsdmainutils"
 - "ca-certificates"
-- "python"
+- "python3"
 remotes:
 - "url": "https://github.com/bitcoin/bitcoin.git"
   "dir": "bitcoin"
diff --git a/contrib/gitian-descriptors/gitian-osx.yml b/contrib/gitian-descriptors/gitian-osx.yml
index 87d8007ccb..1d9c31f9e7 100644
--- a/contrib/gitian-descriptors/gitian-osx.yml
+++ b/contrib/gitian-descriptors/gitian-osx.yml
@@ -23,9 +23,9 @@ packages:
 - "libcap-dev"
 - "libz-dev"
 - "libbz2-dev"
-- "python"
-- "python-dev"
-- "python-setuptools"
+- "python3"
+- "python3-dev"
+- "python3-setuptools"
 - "fonts-tuffy"
 remotes:
 - "url": "https://github.com/bitcoin/bitcoin.git"
diff --git a/contrib/gitian-descriptors/gitian-win.yml b/contrib/gitian-descriptors/gitian-win.yml
index 31b9c309c7..2f1fb14c10 100644
--- a/contrib/gitian-descriptors/gitian-win.yml
+++ b/contrib/gitian-descriptors/gitian-win.yml
@@ -20,7 +20,7 @@ packages:
 - "nsis"
 - "zip"
 - "ca-certificates"
-- "python"
+- "python3"
 - "rename"
 remotes:
 - "url": "https://github.com/bitcoin/bitcoin.git"
diff --git a/contrib/linearize/README.md b/contrib/linearize/README.md
index 2985106982..25a1c7351a 100644
--- a/contrib/linearize/README.md
+++ b/contrib/linearize/README.md
@@ -1,6 +1,5 @@
 # Linearize
-Construct a linear, no-fork, best version of the Bitcoin blockchain. The scripts
-run using Python 3 but are compatible with Python 2.
+Construct a linear, no-fork, best version of the Bitcoin blockchain.
 
 ## Step 1: Download hash list
 
diff --git a/contrib/linearize/linearize-data.py b/contrib/linearize/linearize-data.py
index 56c1fbfc92..468aec04b5 100755
--- a/contrib/linearize/linearize-data.py
+++ b/contrib/linearize/linearize-data.py
@@ -16,7 +16,7 @@ import hashlib
 import datetime
 import time
 from collections import namedtuple
-from binascii import hexlify, unhexlify
+from binascii import unhexlify
 
 settings = {}
 
@@ -61,7 +61,7 @@ def calc_hash_str(blk_hdr):
     hash = calc_hdr_hash(blk_hdr)
     hash = bufreverse(hash)
     hash = wordreverse(hash)
-    hash_str = hexlify(hash).decode('utf-8')
+    hash_str = hash.hex()
     return hash_str
 
 def get_blk_dt(blk_hdr):
@@ -213,7 +213,7 @@ class BlockDataCopier:
 
             inMagic = inhdr[:4]
             if (inMagic != self.settings['netmagic']):
-                print("Invalid magic: " + hexlify(inMagic).decode('utf-8'))
+                print("Invalid magic: " + inMagic.hex())
                 return
             inLenLE = inhdr[4:]
             su = struct.unpack("<I", inLenLE)
diff --git a/contrib/zmq/zmq_sub3.4.py b/contrib/zmq/zmq_sub3.4.py
deleted file mode 100644
index 66fdf7887f..0000000000
--- a/contrib/zmq/zmq_sub3.4.py
+++ /dev/null
@@ -1,90 +0,0 @@
-#!/usr/bin/env python3
-# Copyright (c) 2014-2018 The Bitcoin Core developers
-# Distributed under the MIT software license, see the accompanying
-# file COPYING or http://www.opensource.org/licenses/mit-license.php.
-
-"""
-    ZMQ example using python3's asyncio
-
-    Bitcoin should be started with the command line arguments:
-        bitcoind -testnet -daemon \
-                -zmqpubrawtx=tcp://127.0.0.1:28332 \
-                -zmqpubrawblock=tcp://127.0.0.1:28332 \
-                -zmqpubhashtx=tcp://127.0.0.1:28332 \
-                -zmqpubhashblock=tcp://127.0.0.1:28332
-
-    We use the asyncio library here.  `self.handle()` installs itself as a
-    future at the end of the function.  Since it never returns with the event
-    loop having an empty stack of futures, this creates an infinite loop.  An
-    alternative is to wrap the contents of `handle` inside `while True`.
-
-    The `@asyncio.coroutine` decorator and the `yield from` syntax found here
-    was introduced in python 3.4 and has been deprecated in favor of the `async`
-    and `await` keywords respectively.
-
-    A blocking example using python 2.7 can be obtained from the git history:
-    https://github.com/bitcoin/bitcoin/blob/37a7fe9e440b83e2364d5498931253937abe9294/contrib/zmq/zmq_sub.py
-"""
-
-import binascii
-import asyncio
-import zmq
-import zmq.asyncio
-import signal
-import struct
-import sys
-
-if (sys.version_info.major, sys.version_info.minor) < (3, 4):
-    print("This example only works with Python 3.4 and greater")
-    sys.exit(1)
-
-port = 28332
-
-class ZMQHandler():
-    def __init__(self):
-        self.loop = asyncio.get_event_loop()
-        self.zmqContext = zmq.asyncio.Context()
-
-        self.zmqSubSocket = self.zmqContext.socket(zmq.SUB)
-        self.zmqSubSocket.setsockopt(zmq.RCVHWM, 0)
-        self.zmqSubSocket.setsockopt_string(zmq.SUBSCRIBE, "hashblock")
-        self.zmqSubSocket.setsockopt_string(zmq.SUBSCRIBE, "hashtx")
-        self.zmqSubSocket.setsockopt_string(zmq.SUBSCRIBE, "rawblock")
-        self.zmqSubSocket.setsockopt_string(zmq.SUBSCRIBE, "rawtx")
-        self.zmqSubSocket.connect("tcp://127.0.0.1:%i" % port)
-
-    @asyncio.coroutine
-    def handle(self) :
-        msg = yield from self.zmqSubSocket.recv_multipart()
-        topic = msg[0]
-        body = msg[1]
-        sequence = "Unknown"
-        if len(msg[-1]) == 4:
-          msgSequence = struct.unpack('<I', msg[-1])[-1]
-          sequence = str(msgSequence)
-        if topic == b"hashblock":
-            print('- HASH BLOCK ('+sequence+') -')
-            print(binascii.hexlify(body))
-        elif topic == b"hashtx":
-            print('- HASH TX  ('+sequence+') -')
-            print(binascii.hexlify(body))
-        elif topic == b"rawblock":
-            print('- RAW BLOCK HEADER ('+sequence+') -')
-            print(binascii.hexlify(body[:80]))
-        elif topic == b"rawtx":
-            print('- RAW TX ('+sequence+') -')
-            print(binascii.hexlify(body))
-        # schedule ourselves to receive the next message
-        asyncio.ensure_future(self.handle())
-
-    def start(self):
-        self.loop.add_signal_handler(signal.SIGINT, self.stop)
-        self.loop.create_task(self.handle())
-        self.loop.run_forever()
-
-    def stop(self):
-        self.loop.stop()
-        self.zmqContext.destroy()
-
-daemon = ZMQHandler()
-daemon.start()