CODEWITHSUNDEEP
python
mya205
mya205

Reputation: 83

Unhashable type: ‘list’, trying to subtract a list from a list

I am trying to run code which can find installed packages within my Python environment and install those which are not found within requirements.txt. I keep getting an error on the line:

required = {requirements}

Here is my code so far:

with open ('requirements.txt', "r") as myfile:
        requirements = myfile.read().splitlines()
        #requirements=myfile.readlines()
        #requirements=myfile.read().replace('\n', '')
        print(requirements)
#file_read('test.txt')

required = {requirements}
installed = {pkg.key for pkg in pkg_resources.working_set}
missing = required - installed

if missing:
    python = sys.executable
    subprocess.check_call([python, '-m', 'pip', 'install', *missing], stdout=subprocess.DEVNULL)
else:
    print("prerequisites found")

I keep getting the 'Unhashable' error which I know has something to do with the extracted list but I am not sure how to tackle the problem.

Thanks in advance.

Upvotes: 0

Views: 155

Answers (1)

tdelaney
tdelaney

Reputation: 77347

The problem is that you are trying to add the single list object to the set. Lists are mutable and not hashable, so it fails. Instead, you want to put the values of the list into the set. Either set(requirements), {*requirements} or {line for line in requirements} will do.

>>> requirements = "foo\nbar\nbaz".splitlines()
>>> requirements
['foo', 'bar', 'baz']
>>> {requirements}
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unhashable type: 'list'
>>> set(requirements)
{'foo', 'bar', 'baz'}

Upvotes: 1

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