90 lines
3.0 KiB
Plaintext
90 lines
3.0 KiB
Plaintext
Private attributes which are written but never read are a case of "dead store". Changing their value is useless and most probably indicates an error in the code.
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== Why is this an issue?
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Python has no real private attribute. Every attribute is accessible. There are however two conventions indicating that an attribute is not meant to be "public":
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* attributes with a name starting with a single underscore (ex: ``++_myattribute++``) should be seen as non-public and might change without prior notice. They should not be used by third-party libraries or software. It is ok to use those methods inside the library defining them but it should be done with caution.
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* "class-private" attributes have a name starting with at least two underscores and ending with at most one underscore. These attributes' names will be automatically mangled to avoid collision with subclasses' attributes. For example ``++__myattribute++`` will be renamed as ``++_classname__myattribute++``, where ``++classname++`` is the attribute's class name without its leading underscore(s). They shouldn't be used outside of the class defining the attribute.
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This rule raises an issue when a class-private attribute (two leading underscores, max one underscore at the end) is never read inside the class. It optionally raises an issue on unread attributes prefixed with a single underscore. Both class attributes and instance attributes will raise an issue.
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== How to fix it
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Remove the attribute or fix the code to read it.
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=== Code examples
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==== Noncompliant code example
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[source,python]
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----
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class Noncompliant:
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_class_attr = 0 # Noncompliant if enable_single_underscore_issues is enabled
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__mangled_class_attr = 1 # Noncompliant
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def __init__(self, value):
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self._attr = 0 # Noncompliant if enable_single_underscore_issues is enabled
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self.__mangled_attr = 1 # Noncompliant
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def compute(self, x):
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return x * x
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----
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==== Compliant solution
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[source,python]
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----
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class Compliant:
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_class_attr = 0
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__mangled_class_attr = 1
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def __init__(self, value):
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self._attr = 0
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self.__mangled_attr = 1
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def compute(self, x):
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return x * Compliant._class_attr * Compliant.__mangled_class_attr * self._attr * self.__mangled_attr
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----
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== Resources
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=== Documentation
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* https://docs.python.org/3.8/tutorial/classes.html#private-variables[Python documentation – Private Variables]
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* https://www.python.org/dev/peps/pep-0008/#designing-for-inheritance[PEP 8 – Style Guide for Python Code]
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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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=== Message
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Remove this unread private attribute 'xxxx' or refactor the code to use its value.
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=== Highlighting
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* primary: first attribute assignment
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* secondary: other statements changing its value
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message: 'Also modified here.'
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=== Parameters
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.enableSingleUnderscoreIssues
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****
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_Boolean_
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----
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False
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----
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Enable issues on unread attributes with a single underscore prefix
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****
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endif::env-github,rspecator-view[]
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