Split list of emails and numbers, construct dictionary with emails as keys and auto-incremented numeric values

Question

I've been struggling with this assignment for a few days and can't figure out how to write proper pythonic code to replace the values in the lists when there are pipes in the list strings.

• We have 2 variables: fr and d. fr is a list of strings and d is a dictionary with email addresses as keys and numbers as values (numbers in string format).
• Write code to replace the email address in each of the strings in the fr list with the associated value of that email looked up from the dictionary d.
  • If the dictionary does not contain the email found in the list, add a new entry in the dictionary for the email found in the fr list. The value for this new email key will be the next highest value number in the dictionary in string format.
• Once the dictionary is populated with this new email key and a new number value, replace that email's occurrence in the fr list with the number value.
• Don't manually change fr and d.

Sample input:

fr = [
'7@comp1.COM|4|11|GDSPV',
'7@comp1.COM|16|82|GDSPV',
'13@comp1.COM|12|82|GDSPV',
'26@comp1.COM|19|82|GDSPV'
]

d = {
'7@comp1.COM': '199',
'8@comp4.COM': '200',
'13@comp1.COM': '205'
}

The assignment gives what the output should look like, but I'm struggling to get there because of the pipes:

Value of fr:
['199|4|11|GDSPV', '199|16|82|GDSPV', '205|12|82|GDSPV', '206|19|82|GDSPV']
Value of d:
{'7@comp1.COM': '199', '8@comp4.COM': '200', '13@comp1.COM': '205', '26@comp1.COM': '206'}

This is what the assignment gives you to start off:

line_list = []
for line in fr:

And this is what I have so far:

line_list = []
for line in fr:
    pipes = line.split('|')
    if pipes[0] == '7@comp1.COM':
        pipes[0] = d['7@comp1.COM']
    
    elif pipes[0] == '13@comp1.COM':
        pipes[0] = d['13@comp1.COM']

    elif pipes[0] == '26@comp1.COM':
        pipes[0] = d['26@comp1.COM']
    print(pipes)

    if len(d) < 4:
        d['26@comp1.COM'] = '206'

print("Value of fr: ")
print(fr)
print("Value of d:")
print(d)

Which outputs:

['199', '4', '11', 'GDSPV']
['199', '16', '82', 'GDSPV']
['205', '12', '82', 'GDSPV']
['206', '19', '82', 'GDSPV']
Value of fr: 
['7@comp1.COM|4|11|GDSPV', '7@comp1.COM|16|82|GDSPV', '13@comp1.COM|12|82|GDSPV', '26@comp1.COM|19|82|GDSPV']
Value of d:
{'7@comp1.COM': '199', '8@comp4.COM': '200', '13@comp1.COM': '205', '26@comp1.COM': '206'}

Answer 1

Here's a complete solution:

fr = [
    '7@comp1.COM|4|11|GDSPV',
    '7@comp1.COM|16|82|GDSPV',
    '13@comp1.COM|12|82|GDSPV',
    '26@comp1.COM|19|82|GDSPV'
]

d = {
    '7@comp1.COM': '199',
    '8@comp4.COM': '200',
    '13@comp1.COM': '205'
}

# Figure out the highest key value in the `d` dictionary and set `next_id` to be one greater than that
next_id = -1
for id in d.values():
    if int(id) > next_id:
        next_id = int(id)
next_id += 1

# Create the start of the list we're going to build up
r = []

# For each input in `fr`...
for line in fr:

    # Split the input into elements
    elements = line.split('|')

    # Extract the email address
    email = elements[0]

    # Is this address in `d`?
    if email not in d:
        # No, so add it with the next id as its value
        d[email] = str(next_id)
        next_id += 1

    # Replace the email element with the value for that email from `d`
    elements[0] = d[email]

    # Concatenate the elements back together and put the resulting string in our results list `r`
    r.append('|'.join(elements))

# Print our three structures
print(f"Value of fr: {fr}")
print(f"Value of d: {d}")
print(f"Value of r: {r}")

Result:

Value of fr: ['7@comp1.COM|4|11|GDSPV', '7@comp1.COM|16|82|GDSPV', '13@comp1.COM|12|82|GDSPV', '26@comp1.COM|19|82|GDSPV']
Value of d: {'7@comp1.COM': '199', '8@comp4.COM': '200', '13@comp1.COM': '205', '26@comp1.COM': '206'}
Value of r: ['199|4|11|GDSPV', '199|16|82|GDSPV', '205|12|82|GDSPV', '206|19|82|GDSPV']

Notice that we don't have to know what any of the email addresses are. We just process whatever we find. I wasn't sure what "the next highest value number in the dictionary " meant, so maybe what I did to come up with the next value to use in the dictionary needs to be changed if my interpretation of that is incorrect.

Answer 2

I think str.partition is a bit cuter than str.split in this case. There's no need to split on all pipes. Doing it this way also avoids having to explicitly join with pipes again afterwards, though you still have to join. replaced_fr in this case will be the list containing the replaced, desired output.

replaced_fr = []

for line in fr:
    email, *partitions = line.partition("|")
    value = d.get(email, None)
    if value is None:
        value = str(max(map(int, d.values())) + 1)
        d[email] = value
    replaced_line = "".join([value] + partitions)
    replaced_fr.append(replaced_line)

Answer 3

I think you're forgetting to join the elements of the list. "|".join(pipes) will give you the final string. From there, all you have to do is to append to line_list and print it out after the loop. That isn't the way I'd do it, though. I would look abstract it into a function. In particular:

def substitute(string):
    email, *rest = string.split('|')
    number = d[email]
    return '|'.join([number] + rest)

line_list = []
for line in fr:
    line_list.append(substitute(line))
fr = line_list