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#!/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}
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