Bump minimum python version to 3.6

.python-version

@@ -1 +1 @@
-3.5.6
+3.6.12

.travis.yml

@@ -57,7 +57,7 @@ jobs:
       env:
       cache: pip
       language: python
-      python: '3.5' # Oldest supported version according to doc/dependencies.md
+      python: '3.6' # Oldest supported version according to doc/dependencies.md
       install:
         - set -o errexit; source ./ci/lint/04_install.sh
       before_script:
@@ -83,7 +83,7 @@ jobs:
         FILE_ENV="./ci/test/00_setup_env_i686_centos.sh"
 
     - stage: test
-      name: 'x86_64 Linux  [GOAL: install]  [xenial]  [no wallet]'
+      name: 'x86_64 Linux  [GOAL: install]  [bionic]  [no wallet]'
       env: >-
         FILE_ENV="./ci/test/00_setup_env_native_nowallet.sh"
 

ci/test/00_setup_env_native_nowallet.sh

@@ -7,8 +7,8 @@
 export LC_ALL=C.UTF-8
 
 export CONTAINER_NAME=ci_native_nowallet
-export DOCKER_NAME_TAG=ubuntu:16.04  # Use xenial to have one config run the tests in python3.5, see doc/dependencies.md
-export PACKAGES="python3-zmq clang-3.8 llvm-3.8"  # Use clang-3.8 to test C++11 compatibility, see doc/dependencies.md
+export DOCKER_NAME_TAG=ubuntu:18.04  # Use bionic to have one config run the tests in python3.6, see doc/dependencies.md (3.6 is not available in xenial/16.04)
+export PACKAGES="python3-zmq clang-3.9 llvm-3.9"  # Use clang-3.9 to test C++11 compatibility, see doc/dependencies.md (3.8 is not available in bionic)
 export DEP_OPTS="NO_WALLET=1"
 export GOAL="install"
-export BITCOIN_CONFIG="--enable-glibc-back-compat --enable-reduce-exports CC=clang-3.8 CXX=clang++-3.8 --with-boost-process"
+export BITCOIN_CONFIG="--enable-glibc-back-compat --enable-reduce-exports CC=clang-3.9 CXX=clang++-3.9 --with-boost-process"

configure.ac

@@ -107,8 +107,8 @@ AC_PATH_TOOL(STRIP, strip)
 AC_PATH_TOOL(GCOV, gcov)
 AC_PATH_TOOL(LLVM_COV, llvm-cov)
 AC_PATH_PROG(LCOV, lcov)
-dnl Python 3.5 is specified in .python-version and should be used if available, see doc/dependencies.md
-AC_PATH_PROGS([PYTHON], [python3.5 python3.6 python3.7 python3.8 python3 python])
+dnl Python 3.6 is specified in .python-version and should be used if available, see doc/dependencies.md
+AC_PATH_PROGS([PYTHON], [python3.6 python3.7 python3.8 python3.9 python3 python])
 AC_PATH_PROG(GENHTML, genhtml)
 AC_PATH_PROG([GIT], [git])
 AC_PATH_PROG(CCACHE,ccache)

doc/dependencies.md

@@ -18,7 +18,7 @@ These are the dependencies currently used by Bitcoin Core. You can find instruct
 | librsvg | |  |  |  |  |
 | MiniUPnPc | [2.0.20180203](https://miniupnp.tuxfamily.org/files) |  | No |  |  |
 | PCRE |  |  |  |  | [Yes](https://github.com/bitcoin/bitcoin/blob/master/depends/packages/qt.mk) |
-| Python (tests) |  | [3.5](https://www.python.org/downloads) |  |  |  |
+| Python (tests) |  | [3.6](https://www.python.org/downloads) |  |  |  |
 | qrencode | [3.4.4](https://fukuchi.org/works/qrencode) |  | No |  |  |
 | Qt | [5.9.8](https://download.qt.io/official_releases/qt/) | [5.5.1](https://github.com/bitcoin/bitcoin/issues/13478) | No |  |  |
 | SQLite | [3.32.1](https://sqlite.org/download.html) | [3.7.17](https://github.com/bitcoin/bitcoin/pull/19077) |  |  |  |