TypeError : Unhashable type

Question

I am trying to get a list of list of tuples : something like [ [(1,0),(2,0),(3,0)],[(1,1),(2,1),(3,1)....]] I used this statement

set([(a,b)for         


        

Answer 1

You are creating a set via set(...) call, and set needs hashable items. You can't have set of lists. Because list's arent hashable.

[[(a,b) for a in range(3)] for b in range(3)] is a list. It's not a hashable type. The __hash__ you saw in dir(...) isn't a method, it's just None.

A list comprehension returns a list, you don't need to explicitly use list there, just use:

>>> [[(a,b) for a in range(3)] for b in range(3)]
[[(0, 0), (1, 0), (2, 0)], [(0, 1), (1, 1), (2, 1)], [(0, 2), (1, 2), (2, 2)]]

Try those:

>>> a = {1, 2, 3}
>>> b= [1, 2, 3]
>>> type(a)

>>> type(b)

>>> {1, 2, []}
Traceback (most recent call last):
  File "", line 1, in 
TypeError: unhashable type: 'list'
>>> print([].__hash__)
None
>>> [[],[],[]] #list of lists
[[], [], []]
>>> {[], [], []} #set of lists
Traceback (most recent call last):
  File "", line 1, in 
TypeError: unhashable type: 'list'