python: unhashable type error

Question

Traceback (most recent call last):
  File "<pyshell#80>", line 1, in <module>
    do_work()
  File "C:\pythonwork\readthefile080410.py", line 14, in do_work
    populate_frequency5(e,data)
  File "C:\pythonwork\readthefile080410.py", line 157, in populate_frequency5
    data=medications_minimum3(data,[drug.upper()],1)
  File "C:\pythonwork\readthefile080410.py", line 120, in medications_minimum3
    counter[row[11]]+=1
TypeError: unhashable type: 'list'

i am getting this error on this line:

data=medications_minimum3(data,[drug.upper()],1)

(i have also tried drug.upper() without brackets

here is a preview of this function:

def medications_minimum3(c,drug_input,sample_cutoff): #return sample cut off for # medications/physician
  d=[]
  counter=collections.defaultdict(int)
  for row in c:
    counter[row[11]]+=1
  for row in c:
    if counter[row[11]]>=sample_cutoff:
      d.append(row) 
  write_file(d,'/pythonwork/medications_minimum3.csv')
  return d

does anyone know what am i doing wrong here?

i know that what must be wrong is the way i am calling this function, because i call this function from a different location and it works fine:

d=medications_minimum3(c,drug_input,50)

thank you very much for your help!

Answer 1

counter[row[11]]+=1

You don't show what data is, but apparently when you loop through its rows, row[11] is turning out to be a list. Lists are mutable objects which means they cannot be used as dictionary keys. Trying to use row[11] as a key causes the defaultdict to complain that it is a mutable, i.e. unhashable, object.

The easiest fix is to change row[11] from a list to a tuple. Either by doing

counter[tuple(row[11])] += 1

or by fixing it in the caller before data is passed to medications_minimum3. A tuple simply an immutable list, so it behaves exactly like a list does except you cannot change it once it is created.

Answer 2

  File "C:\pythonwork\readthefile080410.py", line 120, in medications_minimum3
    counter[row[11]]+=1
TypeError: unhashable type: 'list'

row[11] is unhashable. It's a list. That is precisely (and only) what the error message means. You might not like it, but that is the error message.

Do this

counter[tuple(row[11])]+=1

Also, simplify.

d= [ row for row in c if counter[tuple(row[11])]>=sample_cutoff ]

Answer 3

As Jim Garrison said in the comment, no obvious reason why you'd make a one-element list out of drug.upper() (which implies drug is a string).

But that's not your error, as your function medications_minimum3() doesn't even use the second argument (something you should fix).

TypeError: unhashable type: 'list' usually means that you are trying to use a list as a hash argument (like for accessing a dictionary). I'd look for the error in counter[row[11]]+=1 -- are you sure that row[11] is of the right type? Sounds to me it might be a list.

Answer 4

I don't think converting to a tuple is the right answer. You need go and look at where you are calling the function and make sure that c is a list of list of strings, or whatever you designed this function to work with

For example you might get this error if you passed [c] to the function instead of c