I'm implementing an exerimental QR code parser and I figured it would be handy to override a list's __getitem__ that takes a given mask into account, like this:
m = [[1, 0], [0, 1]]
def mask(m, i, j):
if i % 2 == 0 or j == 0:
return int(not m[i][j])
return m[i][j]
m2 = list_with_mask(m, mask)
n = m2[0][0]
How can I achieve it in the most Pythonic way?
Quick & dirty implementation, maybe it's better to inherit from the built-in list class.
Not directly what OP asked but but at least it's a start, and you can customize it for your needs.
class CustomNestedObject:
"""Custom weird class to handle __getitem__
TODO: add error handling for strings and other non list/tuple objects
"""
ERRORS = {
'element_doesnt_exist': "You don't have element with such index"
}
def __init__(self, obj):
self._nested = [] # will store nested recursive CustomNestedObject(s)
self._value = None # will store value (for example integer or string)
# recursively parse obj to CustomNestedObject
self._parse_to_self(obj)
def __repr__(self):
"""Method which will return string representation for the nested objects or self._value"""
if not self._nested:
return str(self._value)
else:
return str([x._value for x in self._nested])
def __getitem__(self, index):
# handle error
try:
self._nested[index]
except IndexError:
raise Exception(self.ERRORS['element_doesnt_exist'])
if not self._nested[index]._nested:
# it means that returned object will be self.value
# print(f'trying to access {self._nested[index]._value}')
return self._nested[index]._value
else:
# print('trying to access nested object')
return self._nested[index]
def _parse_to_self(self, obj):
if isinstance(obj, list) or isinstance(obj, tuple):
for item in obj:
self._nested.append(CustomNestedObject(item))
else:
# save as number if obj is not a list or tuple
self._value = obj
if __name__ == '__main__':
x = CustomNestedObject([1, 2, 3, [4, 5]])
print(x[3][1])
print(x[0])
print(x[9])
