diff --git a/test/lint/lint-python-mutable-default-parameters.sh b/test/lint/lint-python-mutable-default-parameters.sh new file mode 100755 index 0000000000..1f9f035d30 --- /dev/null +++ b/test/lint/lint-python-mutable-default-parameters.sh @@ -0,0 +1,52 @@ +#!/usr/bin/env bash +# +# Copyright (c) 2019 The Bitcoin Core developers +# Distributed under the MIT software license, see the accompanying +# file COPYING or http://www.opensource.org/licenses/mit-license.php. +# +# Detect when a mutable list or dict is used as a default parameter value in a Python function. + +export LC_ALL=C +EXIT_CODE=0 +OUTPUT=$(git grep -E '^\s*def [a-zA-Z0-9_]+\(.*=\s*(\[|\{)' -- "*.py") +if [[ ${OUTPUT} != "" ]]; then + echo "A mutable list or dict seems to be used as default parameter value:" + echo + echo "${OUTPUT}" + echo + cat << EXAMPLE +This is how mutable list and dict default parameter values behave: + +>>> def f(i, j=[], k={}): +... j.append(i) +... k[i] = True +... return j, k +... +>>> f(1) +([1], {1: True}) +>>> f(1) +([1, 1], {1: True}) +>>> f(2) +([1, 1, 2], {1: True, 2: True}) + +The intended behaviour was likely: + +>>> def f(i, j=None, k=None): +... if j is None: +... j = [] +... if k is None: +... k = {} +... j.append(i) +... k[i] = True +... return j, k +... +>>> f(1) +([1], {1: True}) +>>> f(1) +([1], {1: True}) +>>> f(2) +([2], {2: True}) +EXAMPLE + EXIT_CODE=1 +fi +exit ${EXIT_CODE}