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

• Nitin Pawar: 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.
• Phil: Have you considered using the csv module for this?
• Alexander: 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.
• Sheikh Arbaz: Why don't you directly use pandas data frame's read_csv method?

Answer 1

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))

• daveb: Thanks Corentin!. I tried the first way above and the readShpFile method now works as expected!. Thank you so much! Dave
• daveb: Thanks also Corentin for the CSV module documentation link, Much appreciated!

Answer 2

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]

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