45 lines
1.3 KiB
Plaintext
45 lines
1.3 KiB
Plaintext
== Why is this an issue?
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A common anti-pattern is to check that a key does not exist in a dictionary before adding it with a corresponding value. This pattern works but is less readable than the equivalent call to the built-in dictionary method "setdefault()".
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Note that if a default value is set for every key of the dictionary it is possible to use python's ``++defaultdict++`` instead.
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This rule raises an issue when a key presence is checked before being set. It only raises an issue when the value is a hard-coded string, number, list, dictionary or tuple. Computed values will not raise an issue as they can have side-effects.
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=== Noncompliant code example
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[source,python]
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----
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if "key" not in my_dictionary:
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my_dictionary["key"] = ["a", "b", "c"] # Noncompliant
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if "key" not in my_dictionary:
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my_dictionary["key"] = generate_value() # Compliant. No issue is raised as generate_value() might have some side-effect.
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----
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=== Compliant solution
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[source,python]
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----
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my_dictionary.setdefault("key", ["a", "b", "c"])
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# OR, if ["a", "b", "c"] is the default value for every key
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from collections import defaultdict
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my_dictionary = defaultdict(lambda: ["a", "b", "c"])
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----
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ifdef::env-github,rspecator-view[]
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'''
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== Implementation Specification
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(visible only on this page)
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include::message.adoc[]
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endif::env-github,rspecator-view[]
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