Remove item from list that present in dictionary

inventory = {
'gold' : [500,50],
'pouch' : ['flint', 'twine', 'gemstone'], # Assigned a new list to 'pouch' key
'backpack' : ['xylophone','dagger', 'bedroll','bread loaf'].sort(),'pocket':      ['seashell','strange berry','lint']
}

for removing 'dagger' in the list stored in the 'backpack' key, i tried:
del(inventory['backpack'][1])

and
inventory['backpack'].remove(1)

and
inventory['backpack'].remove(["backpack"][1])

But stil the error
Traceback (most recent call last):
  File "python", line 6, in <module>
AttributeError: 'NoneType' object has no attribute 'remove'

What should I do ?

Because you set 'backpack' to this:
['xylophone','dagger', 'bedroll','bread loaf'].sort()

.sort() sorts a list in-place and returns None.  So inventory['backpack'] is None.
Either sort the list after you build the inventory:
inventory = ...
inventory['backpack'].sort()

Or use sorted:
'backpack': list(sorted(['xylophone', 'dagger', 'bedroll', 'bread loaf'])),