97 lines
2.8 KiB
Plaintext
97 lines
2.8 KiB
Plaintext
:link-with-uscores1: https://docs.python.org/3/reference/datamodel.html#object.__getitem__
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:link-with-uscores2: https://docs.python.org/3/reference/datamodel.html#object.__class_getitem__
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:link-with-uscores3: https://docs.python.org/3/reference/datamodel.html#object.__setitem__
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:link-with-uscores4: https://docs.python.org/3/reference/datamodel.html#object.__delitem__
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Getting, setting and deleting items using square brackets requires the accessed object to have special methods:
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* Getting items such as ``++my_variable[key]++`` requires ``++my_variable++`` to have the {link-with-uscores1}[``++__getitem__++``] method, or the {link-with-uscores2}[``++__class_getitem__++``] method if ``++my_variable++`` is a class.
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* Setting items such as ``++my_variable[key] = 42++`` requires ``++my_variable++`` to have the {link-with-uscores3}[``++__setitem__++``] method.
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* Deleting items such as ``++del my_variable[key]++`` requires ``++my_variable++`` to have the {link-with-uscores4}[``++__delitem__++``] method.
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This rule raises an issue when an item operation is performed on an object which doesn't have the corresponding method.
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== Noncompliant Code Example
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----
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del (1, 2)[0] # Noncompliant, tuples are immutable
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(1, 2)[0] = 42 # Noncompliant
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(1, 2)[0]
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class A:
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def __init__(self, values):
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self._values = values
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a = A([0,1,2])
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a[0] # Noncompliant
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del a[0] # Noncompliant
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a[0] = 42 # Noncompliant
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class B:
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pass
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B[0] # Noncompliant
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----
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== Compliant Solution
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----
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del [1, 2][0] # Lists are mutable
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[1, 2][0] = 42
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[1, 2][0]
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class A:
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def __init__(self, values):
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self._values = values
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def __getitem__(self, key):
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return self._values[key]
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def __setitem__(self, key, value):
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self._values[key] = value
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def __delitem__(self, key):
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del self._values[key]
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a = A([0,1,2])
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a[0]
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del a[0]
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a[0] = 42
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class B:
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def __class_getitem__(cls, key):
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return [0, 1, 2, 3][key]
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B[0]
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----
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:link-with-uscores1: https://docs.python.org/3/reference/datamodel.html#object.__getitem__
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:link-with-uscores2: https://docs.python.org/3/reference/datamodel.html#object.__setitem__
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:link-with-uscores3: https://docs.python.org/3/reference/datamodel.html#object.__delitem__
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:link-with-uscores4: https://docs.python.org/3/reference/datamodel.html#object.__class_getitem__
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== See
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* {link-with-uscores1}[Python documentation - ++__getitem__++ method]
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* {link-with-uscores2}[Python documentation - ++__setitem__++ method]
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* {link-with-uscores3}[Python documentation - ++__delitem__++ method]
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* {link-with-uscores4}[Python documentation - ++__class_getitem__++ method]
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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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include::highlighting.adoc[]
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endif::env-github,rspecator-view[]
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