So from what I've gathered user-made classes are supposed to be mutable by default, but I've experienced the opposite. Here's my code:
import copy
class vector:
def __init__(self, entries):
if type(entries) == list:
self.elements = []
self.dimensionality = len(entries)
for entry in entries:
self.elements.append(entry)
elif type(entries) == vector:
self.elements = entries.elements
def __getitem__(self,index):
return self.elements[index]
def __add__(self, otherVector):
if len(self) != len(otherVector):
raise RuntimeError("Cannot add these vectors")
sumt = []
for entry in len(self):
sumt.append(self.elements[entry] + otherVector.elements[entry])
return vector(sumt)
def __len__(self):
return len(self.elements)
def __eq__(self, otherVariable):
return size(self) == size(otherVariable)
def size(x):
return (x * x)**(1/2)
def taxi(x):
taxiSize = 0
for entry in x.elements:
taxiSize += entry
return taxiSize
class matrix:
def __init__(self, entries):
for i in entries:
if len(entries[0]) != len(i):
raise RuntimeError("All rows of matrix must contain the same number of entries")
self.elements = []
for row in entries:
self.elements.append(vector(row))
def __add__(self, otherMatrix):
if len(self.elements) != len(otherMatrix.elements):
raise RuntimeError("Cannot add matrices of different sizes")
if len(self.elements[0]) != len(otherMatrix.elements[0]):
raise RuntimeError("Cannot add matrices of different sizes")
sumt = []
row = []
for entry in self.elements[0]:
row.append(0)
for i in self.elements:
sumt.append(row)
sumf = matrix(sumt)
for i in range(len(self.elements)):
for j in range(len(self.elements[0])):
sumf.elements[i][j] = self.elements[i][j] + otherMatrix.elements[i][j] #error is on this line
return sumf
matrix([[3,4],[1,2]]) + matrix([[3,4],[1,2]])
And the error:
Traceback (most recent call last):
File "/Users/sebpole/Documents/vectors.py", line 164, in <module>
matrix([[3,4],[1,2]]) + matrix([[3,4],[1,2]])
File "/Users/sebpole/Documents/vectors.py", line 143, in __add__
sumf.elements[i][j] = self.elements[i][j] + otherMatrix.elements[i][j]
TypeError: 'vector' object does not support item assignment
seems like Python doesn't like my changing the entries of my vector class, which is confusing me because I thought the class was supposed to be immutable.
Why is my object immutable, and how can I fix this?
通过__setitem__()
方法启用项目分配,您的类未定义该方法 。
This is not a question of mutability. This is a question of whether your class supports an indexed assignment.
To recreate the problem:
v0 = vector(..)
v1 = vector(..)
v0[0] = v1 # doesn't make sense with current implementation!
Your custom vector class doesn't support this operation, is the reason for the failure.
EDIT: As @Ignacio has pointed out, you need the __setitem__()
method defined, but you also need the __get_item()__
method (to allow v0[0] + v1[0]
to work ) defined as well.
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