Trying to understand dictionaries

Question

I am playing about with Python, trying to understand dictionaries. I know questions have been asked before relating to this error, but they don't help me understand my issue.

I have the following code

mailSender = dict()
count = 0
name = input("Enter file:")
handle = open(name)
for line in handle:
    line = line.rstrip()
    if not line.startswith("From "):
        continue
    count = count + 1
    senderNames = line.split()
    # print(splitLines[1])
    print(senderNames[1])

    if senderNames not in mailSender:
        mailSender[senderNames] = 1
    else:
        mailSender[senderNames] = mailSender[senderNames] + 1

# print(mailSender)

I am trying to pick out email addresses for a text file,a nnd then find who sent the most emails.

I keep getting the following error:

if senderNames not in mailSender: TypeError: unhashable type: 'list'

I do not have the experience to see where I am going wrong, and I hope someone can shed some light on it.

Answer 1

A dictionary has 2 parts, keys and values. Each key, points to a value, which is done like so:

mailSender["email@email.com"] = 5 # This means, that email@email.com appears 5 times

When you are trying to look for the name of a sender, you need to search for the name in the keys where all the emails are stored, not the entire dictionary, which is a mapping for keys to values. You also need to indicate the position of the email address you want to find in senderNames, which is 1 of the list of emails. You can solve your problem, by changing your code to:

if senderNames[*index of name*] not in mailSender.keys():
    mailSender[senderNames] = 1
else:
    mailSender[senderNames] = mailSender[senderNames] + 1

For example, you could refer to finding the first email address like this:

if senderNames[0] not in mailSender.keys():
    mailSender[senderNames] = 1
else:
    mailSender[senderNames] = mailSender[senderNames] + 1

It will then search for if senderNames is in the keys of mailSender. Hope this helped!