Python Error while trying to read form a csv file to a dictionary

Question

I am trying to read from a csv file to a dictionary. The problem is that I have 3 values per line (not just 2) and want to transform to a dict where the first value is the key and the last 2 values are combined to a single value (eg using a list or a tuple). As an example, I have the following inside csv:

Calcium Enriched 100% Lactose Free Fat Free Milk,2346,57876.0

Large Organic Omega3 Brown Eggs,2568,86280.0

Roasted & Salted Shelled Pistachios,919,29358.0

Chocolate Peanut Butter Protein Bar,801,21296.0

...

I want the output to be something like this:

{'Calcium Enriched 100% Lactose Free Fat Free Milk': [2346,57876.0]}

{'Large Organic Omega3 Brown Eggs': [2568,86280.0]}

{'Roasted & Salted Shelled Pistachios': [919,29358.0]}

{'Chocolate Peanut Butter Protein Bar': [801,21296.0]}

I tried to do it the normal way like this:

with open('avg_prod_reorder_time.csv', 'r', encoding='utf-8') as csv_file:
    reader = csv.reader(csv_file)
    avg_prod_reorder_time = dict(reader)

But I get the following error:

ValueError: dictionary update sequence element #0 has length 3; 2 is required

How to fix this? Thanks.

Answer 1

You needn't use csv. Just read files line by line and split it.

with open("data.csv", 'r') as f:
    for line in f:
        key, *value = line.rstrip("\n").split(',')
        result = {key: list(value)}

Answer 2

This creates a dict as you wanted:

avg_prod_reorder_time = {r[0]: r[1:] for r in reader if r}

A dict consists of key/value pairs, but your data is not formatted in pairs. The code above takes the first element as a key and forms a list of all remaining elements. The condition if r skips empty rows.

Answer 3

Consider you have a csv file like this,

some.csv

Hello ,1,2
There ,2,3
Friend ,4,5

You can try this,

import csv
mydict = {}
with open("some.csv","r+") as c:
    r = csv.reader(c)
    for row in r:
        mydict[row[0]] = row[1:]
print(mydict)

output:

{'Friend ': ['4', '5'], 'Hello ': ['1', '2'], 'There ': ['2', '3']}

Explanations:

This is the part where you'll be interested in,

r = csv.reader(c)
for row in r:
    mydict[row[0]] = row[1:]

Here we are assigning

mydict[row[0]] with row[1:]

ie for first one

mydict['Hello'] with row[1:] ie [1,2] # List slicing

Similarly for the other lines.

Note:

List slicing means slicing a list based on indexes, try this if you didn't know about them. The general form is like this,

your_list[start:stop]

Note Start is inclusive stop is exclusive

>>> a = [1,2,3,4]
>>> a[0]
1
>>> a[1:]
[2, 3, 4]
>>> a[2:]
[3, 4]
>>> a[3:]
[4]
>>> a[:2]
[1, 2]
>>> a[:3]
[1, 2, 3]
>>> a[:1]
[1]