TypeError: unsupported operand type(s) for -: 'list' and 'list'
Question:
I am trying to implement the Naive Gauss and getting the unsupported operand type error on execution.
Output:
execfile(filename, namespace)
File "/media/zax/MYLINUXLIVE/A0N-.py", line 26, in <module>
print Naive_Gauss([[2,3],[4,5]],[[6],[7]])
File "/media/zax/MYLINUXLIVE/A0N-.py", line 20, in Naive_Gauss
b[row] = b[row]-xmult*b[column]
TypeError: unsupported operand type(s) for -: 'list' and 'list'
>>>
This is the code
def Naive_Gauss(Array,b):
n = len(Array)
for column in xrange(n-1):
for row in xrange(column+1, n):
xmult = Array[row][column] / Array[column][column]
Array[row][column] = xmult
#print Array[row][col]
for col in xrange(0, n):
Array[row][col] = Array[row][col] - xmult*Array[column][col]
b[row] = b[row]-xmult*b[column]
print Array
print b
print Naive_Gauss([[2,3],[4,5]],[[6],[7]])
Answers:
You can’t subtract a list from a list.
>>> [3, 7] - [1, 2]
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: unsupported operand type(s) for -: 'list' and 'list'
Simple way to do it is using numpy
:
>>> import numpy as np
>>> np.array([3, 7]) - np.array([1, 2])
array([2, 5])
You can also use list comprehension, but it will require changing code in the function:
>>> [a - b for a, b in zip([3, 7], [1, 2])]
[2, 5]
>>> import numpy as np
>>>
>>> def Naive_Gauss(Array,b):
... n = len(Array)
... for column in xrange(n-1):
... for row in xrange(column+1, n):
... xmult = Array[row][column] / Array[column][column]
... Array[row][column] = xmult
... #print Array[row][col]
... for col in xrange(0, n):
... Array[row][col] = Array[row][col] - xmult*Array[column][col]
... b[row] = b[row]-xmult*b[column]
... print Array
... print b
... return Array, b # <--- Without this, the function will return `None`.
...
>>> print Naive_Gauss(np.array([[2,3],[4,5]]),
... np.array([[6],[7]]))
[[ 2 3]
[-2 -1]]
[[ 6]
[-5]]
(array([[ 2, 3],
[-2, -1]]), array([[ 6],
[-5]]))
Use Set in Python
>>> a = [2,4]
>>> b = [1,4,3]
>>> set(a) - set(b)
set([2])
This question has been answered but I feel I should also mention another potential cause. This is a direct result of coming across the same error message but for different reasons. If your list/s are empty the operation will not be performed. check your code for indents and typos
The operations needed to be performed, require numpy arrays either created via
np.array()
or can be converted from list to an array via
np.stack()
As in the above mentioned case, 2 lists are inputted as operands it triggers the error.
I am trying to implement the Naive Gauss and getting the unsupported operand type error on execution.
Output:
execfile(filename, namespace)
File "/media/zax/MYLINUXLIVE/A0N-.py", line 26, in <module>
print Naive_Gauss([[2,3],[4,5]],[[6],[7]])
File "/media/zax/MYLINUXLIVE/A0N-.py", line 20, in Naive_Gauss
b[row] = b[row]-xmult*b[column]
TypeError: unsupported operand type(s) for -: 'list' and 'list'
>>>
This is the code
def Naive_Gauss(Array,b):
n = len(Array)
for column in xrange(n-1):
for row in xrange(column+1, n):
xmult = Array[row][column] / Array[column][column]
Array[row][column] = xmult
#print Array[row][col]
for col in xrange(0, n):
Array[row][col] = Array[row][col] - xmult*Array[column][col]
b[row] = b[row]-xmult*b[column]
print Array
print b
print Naive_Gauss([[2,3],[4,5]],[[6],[7]])
You can’t subtract a list from a list.
>>> [3, 7] - [1, 2]
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: unsupported operand type(s) for -: 'list' and 'list'
Simple way to do it is using numpy
:
>>> import numpy as np
>>> np.array([3, 7]) - np.array([1, 2])
array([2, 5])
You can also use list comprehension, but it will require changing code in the function:
>>> [a - b for a, b in zip([3, 7], [1, 2])]
[2, 5]
>>> import numpy as np
>>>
>>> def Naive_Gauss(Array,b):
... n = len(Array)
... for column in xrange(n-1):
... for row in xrange(column+1, n):
... xmult = Array[row][column] / Array[column][column]
... Array[row][column] = xmult
... #print Array[row][col]
... for col in xrange(0, n):
... Array[row][col] = Array[row][col] - xmult*Array[column][col]
... b[row] = b[row]-xmult*b[column]
... print Array
... print b
... return Array, b # <--- Without this, the function will return `None`.
...
>>> print Naive_Gauss(np.array([[2,3],[4,5]]),
... np.array([[6],[7]]))
[[ 2 3]
[-2 -1]]
[[ 6]
[-5]]
(array([[ 2, 3],
[-2, -1]]), array([[ 6],
[-5]]))
Use Set in Python
>>> a = [2,4]
>>> b = [1,4,3]
>>> set(a) - set(b)
set([2])
This question has been answered but I feel I should also mention another potential cause. This is a direct result of coming across the same error message but for different reasons. If your list/s are empty the operation will not be performed. check your code for indents and typos
The operations needed to be performed, require numpy arrays either created via
np.array()
or can be converted from list to an array via
np.stack()
As in the above mentioned case, 2 lists are inputted as operands it triggers the error.