Reading values for CSV file using Python

Question

I am having some problems getting the row values from the CSV file below

CSV
minzoom, maxzoom
0,5
5,10
10,18

My Code :

i = 0
for line in open("C:/Marine/lookup/distinct_lookup_scales.csv"):
    i = i + 1
    if (i > 1):  #Skip header
        print("Line: " + line)
        #csv_row = line.split(',')
        minzoom = str(line[0])
        maxzoom = str(line[2])
        print("Minzoom:" + minzoom)
        print("Maxzoom:" + maxzoom)
        readShpFile(minzoom, maxzoom)

The values returned for minzoom and maxzoom has been

0   5
5   1
1   ,

I had used line split but reverted to trying to get items from the line Not sure if that was the best approach

What you're reading from csv is a string. Indexing won't work. Split will be a good approach. If you have issues with it, post the output or the issue, or both. — Nitin Pawar
– Nitin Pawar, Commented Oct 4, 2018 at 9:59
minzoom, maxzoom = line.split(',')? Indexing doesn't work, as the zoom can be more than 10 which means you need two characters instead of one and you' may need to shift the max zoom location. — Alexander
– Alexander, Commented Oct 4, 2018 at 10:05
Why don't you directly use pandas data frame's read_csv method? — Sheikh Arbaz
– Sheikh Arbaz, Commented Oct 4, 2018 at 10:06

Corentin Limier · Accepted Answer · 2018-10-04 10:11:59Z

3

That is not how you should read the csv file. Take a look at the csv module documentation.

One example :

import csv

with open('C:/Marine/lookup/distinct_lookup_scales.csv', 'r') as csvfile:
    csvreader = csv.reader(csvfile)
    csvreader.next() #skip header
    for row in csvreader:
        minzoom = int(row[0])
        maxzoom = int(row[1])
        print('minzoom : {}'.format(minzoom))
        print('maxzoom : {}'.format(maxzoom))

You can also use a DictReader which will use your header line to yield dictionaries.

import csv

with open('C:/Marine/lookup/distinct_lookup_scales.csv', 'r') as csvfile:
    csvreader = csv.DictReader(csvfile)
    for row in csvreader:
        minzoom = int(row['minzoom'])
        maxzoom = int(row['maxzoom'])
        print('minzoom : {}'.format(minzoom))
        print('maxzoom : {}'.format(maxzoom))

edited Oct 4, 2018 at 10:11

answered Oct 4, 2018 at 10:06

Corentin Limier

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2 Comments

daveb Over a year ago

Thanks Corentin!. I tried the first way above and the readShpFile method now works as expected!. Thank you so much! Dave

daveb Over a year ago

Thanks also Corentin for the CSV module documentation link, Much appreciated!

Y.Wang · Accepted Answer · 2018-10-04 10:08:29Z

0

You can try numpy.genfromtxt, like:

import numpy as np

data = np.genfromtxt("C:/Marine/lookup/distinct_lookup_scales.csv", delimiter = ",",
                     skip_header = 1)
minzooms = data[:,0]
maxzooms = data[:,1]

answered Oct 4, 2018 at 10:08

Y.Wang

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1 Comment

daveb Over a year ago

Thanks Y.Wang. Not used numpy before as I am new to python but will give the approach a try. Dave

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