Merge bitcoin#18210: test: type hints in Python tests

bd7e530 This PR adds initial support for type hints checking in python scripts. (Kiminuo)

Pull request description:

  This PR adds initial support for type hints checking in python scripts.

  Support for type hints was introduced in Python 3.5. Type hints make it easier to read and review code in my opinion. Also an IDE may discover a potential bug sooner. Yet, as PEP 484 says: "It should also be emphasized that Python will remain a dynamically typed language, and the authors have no desire to ever make type hints mandatory, even by convention."

  [Mypy](https://mypy.readthedocs.io/en/latest/index.html) is used in `lint-python.sh` to do the type checking. The package is standard so there is little chance that it will be abandoned. Mypy checks that type hints in source code are correct when they are not, it fails with an error.

  **Notes:**

  * [--ignore-missing-imports](https://mypy.readthedocs.io/en/latest/command_line.html#cmdoption-mypy-ignore-missing-imports) switch is passed on to `mypy` checker for now. The effect of this is that one does not need `# type: ignore` for `import zmq`. More information about import processing can be found [here](https://mypy.readthedocs.io/en/stable/running_mypy.html#missing-imports). This can be changed in a follow-up PR, if it is deemed useful.
  * We are stuck with Python 3.5 until 04/2021 (see https://packages.ubuntu.com/xenial/python3). When Python version is bumped to 3.6+, one can change:
      ```python
      _opcode_instances = []  # type: List[CScriptOp]
      ```
      to
      ```python
      _opcode_instances:List[CScriptOp] = []
      ```
      for type hints that are **not** function parameters and function return types.

  **Useful resources:**

  * https://docs.python.org/3.5/library/typing.html
  * https://www.python.org/dev/peps/pep-0484/

ACKs for top commit:
  fanquake:
    ACK bd7e530 - the type checking is not the most robust (there are things it fails to detect), but I think this is worth adopting (in a limited capacity while we maintain 3.5 compat).
  MarcoFalke:
    ACK bd7e530 fine with me

Tree-SHA512: 21ef213915fb1dec6012f59ef17484e6c9e0abf542a316b63d5f21a7778ad5ebabf8961ef5fc8e5414726c2ee9c6ae07c7353fb4dd337f8fcef5791199c8987a

Author: fanquake

.gitignore

@@ -128,6 +128,7 @@ linux-build
 win32-build
 test/config.ini
 test/cache/*
+test/.mypy_cache/
 
 !src/leveldb*/Makefile
 

ci/lint/04_install.sh

@@ -14,6 +14,7 @@ travis_retry pip3 install codespell==1.17.1
 travis_retry pip3 install flake8==3.8.3
 travis_retry pip3 install vulture==2.3
 travis_retry pip3 install yq
+travis_retry pip3 install mypy==0.700
 
 SHELLCHECK_VERSION=v0.6.0
 curl -s "https://storage.googleapis.com/shellcheck/shellcheck-${SHELLCHECK_VERSION}.linux.x86_64.tar.xz" | tar --xz -xf - --directory /tmp/

test/functional/README.md

@@ -26,10 +26,12 @@ don't have test cases for.
   The Travis linter also checks this, but [possibly not in all cases](https://github.com/bitcoin/bitcoin/pull/14884#discussion_r239585126).
 - See [the python lint script](/test/lint/lint-python.sh) that checks for violations that
   could lead to bugs and issues in the test code.
+- Use [type hints](https://docs.python.org/3/library/typing.html) in your code to improve code readability
+  and to detect possible bugs earlier.
 - Avoid wildcard imports
 - Use a module-level docstring to describe what the test is testing, and how it
   is testing it.
-- When subclassing the BitcoinTestFramwork, place overrides for the
+- When subclassing the BitcoinTestFramework, place overrides for the
   `set_test_params()`, `add_options()` and `setup_xxxx()` methods at the top of
   the subclass, then locally-defined helper methods, then the `run_test()` method.
 - Use `f'{x}'` for string formatting in preference to `'{}'.format(x)` or `'%s' % x`.
@@ -45,7 +47,7 @@ don't have test cases for.
     - `rpc` for tests for individual RPC methods or features, eg `rpc_listtransactions.py`
     - `tool` for tests for tools, eg `tool_wallet.py`
     - `wallet` for tests for wallet features, eg `wallet_keypool.py`
-- use an underscore to separate words
+- Use an underscore to separate words
     - exception: for tests for specific RPCs or command line options which don't include underscores, name the test after the exact RPC or argument name, eg `rpc_decodescript.py`, not `rpc_decode_script.py`
 - Don't use the redundant word `test` in the name, eg `interface_zmq.py`, not `interface_zmq_test.py`
 

test/functional/data/invalid_txs.py

@@ -21,6 +21,7 @@
 """
 import abc
 
+from typing import Optional
 from test_framework.messages import (
     COutPoint,
     CTransaction,
@@ -39,7 +40,7 @@ class BadTxTemplate:
     __metaclass__ = abc.ABCMeta
 
     # The expected error code given by bitcoind upon submission of the tx.
-    reject_reason = ""
+    reject_reason = ""  # type: Optional[str]
 
     # Only specified if it differs from mempool acceptance error.
     block_reject_reason = ""

test/functional/test_framework/script.py

@@ -8,6 +8,7 @@
 """
 import struct
 import unittest
+from typing import List, Dict
 
 from .messages import (
     CTransaction,
@@ -19,7 +20,7 @@
 from .ripemd160 import ripemd160
 
 MAX_SCRIPT_ELEMENT_SIZE = 520
-OPCODE_NAMES = {}
+OPCODE_NAMES = {}  # type: Dict[CScriptOp, str]
 
 def hash160(s):
     return ripemd160(sha256(s))
@@ -35,7 +36,7 @@ def bn2vch(v):
     # Serialize to bytes
     return encoded_v.to_bytes(n_bytes, 'little')
 
-_opcode_instances = []
+_opcode_instances = []  # type: List[CScriptOp]
 class CScriptOp(int):
     """A single script opcode"""
     __slots__ = ()

test/functional/test_framework/test_framework.py

@@ -112,6 +112,9 @@ class BitcoinTestFramework(metaclass=BitcoinTestMetaClass):
 
     This class also contains various public and private helper methods."""
 
+    chain = None  # type: str
+    setup_clean_chain = None  # type: bool
+
     def __init__(self):
         """Sets test framework defaults. Do not override this method. Instead, override the set_test_params() method"""
         self.chain: str = 'regtest'
@@ -460,7 +463,7 @@ def run_test(self):
 
     # Public helper methods. These can be accessed by the subclass test scripts.
 
-    def add_nodes(self, num_nodes, extra_args=None, *, rpchost=None, binary=None, binary_cli=None, versions=None):
+    def add_nodes(self, num_nodes: int, extra_args=None, *, rpchost=None, binary=None, binary_cli=None, versions=None):
         """Instantiate TestNode objects.
 
         Should only be called once after the nodes have been specified in

test/functional/test_runner.py

@@ -43,7 +43,7 @@
 if os.name != 'nt' or sys.getwindowsversion() >= (10, 0, 14393):
     if os.name == 'nt':
         import ctypes
-        kernel32 = ctypes.windll.kernel32
+        kernel32 = ctypes.windll.kernel32  # type: ignore
         ENABLE_VIRTUAL_TERMINAL_PROCESSING = 4
         STD_OUTPUT_HANDLE = -11
         STD_ERROR_HANDLE = -12

test/lint/lint-python.sh

@@ -7,6 +7,7 @@
 # Check for specified flake8 warnings in python files.
 
 export LC_ALL=C
+export MYPY_CACHE_DIR="${BASE_ROOT_DIR}/test/.mypy_cache"
 
 enabled=(
     E101 # indentation contains mixed spaces and tabs
@@ -103,3 +104,5 @@ PYTHONWARNINGS="ignore" $FLAKECMD --ignore=B,C,E,F,I,N,W --select=$(IFS=","; ech
         echo "$@"
     fi
 )
+
+mypy --ignore-missing-imports $(git ls-files "test/functional/*.py")