Reading first n lines of a CSV into a dictionary

Question

I have a CSV file I'd like to read into a dictionary for subsequent insertion into a MongoDB collection entitled projects.

I accomplished this with the following:

with open('opendata_projects.csv') as f:
    records = csv.DictReader(f)
    projects.insert(records)

However, I found my poor sandbox account couldn't hold all the data. In turn, I'd like to read in the first n lines so I can play around with the data and get used to working with MongoDB.

First I checked the docs for the csv.DictReader function:

class csv.DictReader(csvfile, fieldnames=None, restkey=None, restval=None, dialect='excel', *args, **kwds)

But the function doesn't seem to allow for entering in the number of rows I'd like as a parameter.

So I attempted to do so by writing the following code:

with open('opendata_projects.csv') as f:
    records = csv.DictReader(f)
    for i in records:
        if i <= 100:
            projects.insert(i)

Which was followed by the error:

TypeError: unorderable types: dict() <= int()

This prompted me to look into dictionaries further, and I found they are unordered. Nevertheless, it seems an example from the Python csv docs suggests I can iterate with csv.DictReader:

with open('names.csv') as csvfile:
    reader = csv.DictReader(csvfile)
    for row in reader:
        print(row['first_name'], row['last_name'])

Is there a way to accomplish what I'd like to do by using these functions?

Answer 1

You can use itertools.islice, like this

import csv, itertools

with open('names.csv') as csvfile:
    for row in itertools.islice(csv.DictReader(csvfile), 100):
        print(row['first_name'], row['last_name'])

islice will create an iterator from the iterable object you pass and it will allow you iterate till the limit, you pass as the second parameter.

---

Apart from that, if you want to count yourself, you can use enumerate function, like this

for index, row in enumerate(csv.DictReader(csvfile)):
    if index >= 100:
        break
    print(row['first_name'], row['last_name'])