From a little search, that I understand the file should be opened in universal newline mode, which you cannot directly do with a response content (I guess).
To finish the task, you can either save the downloaded content to a temporary file, or process it in memory.
Save as file:
import requests
import csv
import os
temp_file_name = 'temp_csv.csv'
url = 'http://url.to/file.csv'
download = requests.get(url)
with open(temp_file_name, 'w') as temp_file:
temp_file.writelines(download.content)
with open(temp_file_name, 'rU') as temp_file:
csv_reader = csv.reader(temp_file, dialect=csv.excel_tab)
for line in csv_reader:
print line
# delete the temp file after process
os.remove(temp_file_name)
In memory:
(To be updated)