Getting, setting and deleting items using square brackets requires the accessed object to have special methods:
- Getting items such as
my_variable[key] requires my_variable to have the __getitem__ method, or the __class_getitem__ method if
my_variable is a class.
- Setting items such as
my_variable[key] = 42 requires my_variable to have the __setitem__ method.
- Deleting items such as
del my_variable[key] requires my_variable to have the __delitem__ method.
Performing these operations on an object that doesn’t have the corresponding method will result in a TypeError.
To fix this issue, make sure that the class for which you are trying to perform item operations implements the required methods.
Code examples
Noncompliant code example
del (1, 2)[0] # Noncompliant: tuples are immutable
(1, 2)[0] = 42 # Noncompliant
(1, 2)[0]
class A:
def __init__(self, values):
self._values = values
a = A([0,1,2])
a[0] # Noncompliant
del a[0] # Noncompliant
a[0] = 42 # Noncompliant
class B:
pass
B[0] # Noncompliant
Compliant solution
del [1, 2][0] # Lists are mutable
[1, 2][0] = 42
[1, 2][0]
class A:
def __init__(self, values):
self._values = values
def __getitem__(self, key):
return self._values[key]
def __setitem__(self, key, value):
self._values[key] = value
def __delitem__(self, key):
del self._values[key]
a = A([0,1,2])
a[0]
del a[0]
a[0] = 42
class B:
def __class_getitem__(cls, key):
return [0, 1, 2, 3][key]
B[0]
