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a84ec5cc19
e4f4ea47ebf7774fb6f445adde7bf7ea71fa05a1 lint: Catch use of [] or {} as default parameter values in Python functions (practicalswift)
25dd86715039586d92176eee16e9c6644d2547f0 Avoid using mutable default parameter values (practicalswift)
Pull request description:
Avoid common Python default parameter gotcha when mutable `dict`/`list`:s are used as default parameter values.
Examples of this gotcha caught during review:
* https://github.com/bitcoin/bitcoin/pull/16673#discussion_r317415261
* https://github.com/bitcoin/bitcoin/pull/14565#discussion_r241942304
Perhaps surprisingly this is how mutable list and dictionary default parameter values behave in Python:
```
>>> 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})
```
In contrast to:
```
>>> 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})
```
The latter is typically the intended behaviour.
This PR fixes two instances of this and adds a check guarding against this gotcha going forward :-)
ACKs for top commit:
Sjors:
Oh Python... ACK e4f4ea47ebf7774fb6f445adde7bf7ea71fa05a1. Testing tip: swap the two commits.
Tree-SHA512: 56e14d24fc866211a20185c9fdb274ed046c3aed2dc0e07699e58b6f9fa3b79f6d0c880fb02d72b7fe5cc5eb7c0ff6da0ead33123344e1a872209370c2e49e3f
53 lines
1.1 KiB
Bash
Executable File
53 lines
1.1 KiB
Bash
Executable File
#!/usr/bin/env bash
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#
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# Copyright (c) 2019 The Bitcoin Core developers
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# Distributed under the MIT software license, see the accompanying
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# file COPYING or http://www.opensource.org/licenses/mit-license.php.
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#
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# Detect when a mutable list or dict is used as a default parameter value in a Python function.
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export LC_ALL=C
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EXIT_CODE=0
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OUTPUT=$(git grep -E '^\s*def [a-zA-Z0-9_]+\(.*=\s*(\[|\{)' -- "*.py")
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if [[ ${OUTPUT} != "" ]]; then
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echo "A mutable list or dict seems to be used as default parameter value:"
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echo
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echo "${OUTPUT}"
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echo
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cat << EXAMPLE
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This is how mutable list and dict default parameter values behave:
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>>> def f(i, j=[], k={}):
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... j.append(i)
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... k[i] = True
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... return j, k
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...
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>>> f(1)
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([1], {1: True})
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>>> f(1)
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([1, 1], {1: True})
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>>> f(2)
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([1, 1, 2], {1: True, 2: True})
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The intended behaviour was likely:
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>>> def f(i, j=None, k=None):
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... if j is None:
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... j = []
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... if k is None:
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... k = {}
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... j.append(i)
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... k[i] = True
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... return j, k
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...
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>>> f(1)
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([1], {1: True})
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>>> f(1)
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([1], {1: True})
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>>> f(2)
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([2], {2: True})
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EXAMPLE
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EXIT_CODE=1
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fi
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exit ${EXIT_CODE}
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