45c9727f72
Authored-by: guillaume-dequenne-sonarsource <guillaume-dequenne-sonarsource@users.noreply.github.com>
59 lines
1.5 KiB
Plaintext
59 lines
1.5 KiB
Plaintext
This rule raises an issue when an object used as a sequence index does not define an ``++__index__++`` method.
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== Why is this an issue?
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Objects can be used as sequence indexes to access a specific element from the sequence, through the following syntax:
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[source,python]
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----
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my_list = [1, 2, 3, 4]
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x = 1
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print(my_list[x]) # This will print 2
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----
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Whenever an object is used as a sequence index, the Python interpreter calls its ``++__index__++`` method to compute the index that needs to be accessed from the sequence.
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Any object can be used as sequence index, as long as it defines an ``++__index__++`` method that returns an `int`. Most commonly, sequence indexes are simply integers.
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Similarly, sequences can be sliced through the following syntax:
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[source,python]
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----
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my_list = [1, 2, 3, 4]
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x = 1
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print(my_list[1:3]) # This will print [2, 3]
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----
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If an invalid object is used as a sequence index, a `TypeError` will be raised.
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== How to fix it
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Make sure to use an object that defines an ``++__index__++`` method as sequence indexes.
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=== Code examples
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==== Noncompliant code example
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[source,text,diff-id=1,diff-type=noncompliant]
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----
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def foo():
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my_list = ["spam", "eggs"]
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x = my_list["spam"] # Noncompliant: a str is not a valid index
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----
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==== Compliant solution
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[source,text,diff-id=1,diff-type=compliant]
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----
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def foo():
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my_list = ["spam", "eggs"]
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x = my_list[0]
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----
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== Resources
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=== Documentation
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Python Documentation - https://docs.python.org/3/library/operator.html#operator.__index__[__index__ method]
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