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How to rewrite only one field (line[n]) in csv but in same time be able to work with data?

I have a csv file with three lines and three columns here.
This is the csv file
At first I want to print all the lines.
Subsequently, for each of them, program check whether it is written in the second field(index 1) USA. If so, program will take the price from the third field and multiply it by two.
Now I need to rewrite this doubled price instead of 2000 (in line with the USA)
import csv
with open('countries.csv', 'r') as source:
reader = csv.reader(source)
writer = csv.writer(source)
for line in reader:
print(*line, sep=';')
with open('countries.csv', 'r') as source:
reader = csv.reader(source)
for line in reader:
if line[2] == "USA":
actual_price = int(line[2])
print(actual_price)
new_price = int(actual_price) * 2
print(new_price)
Someone has already advised me to use the creation of a new file.
But this causes problems when I want to work with the data in the file first.
import csv
import os
with open('countries.csv', mode='r') as oldfile, open(
'countries.tmp', mode='w', newline='') as newfile:
# define a reader and a writer
reader = csv.reader(oldfile, delimiter=';', quotechar='"')
writer = csv.writer(newfile, delimiter=';', quotechar='"',
quoting=csv.QUOTE_MINIMAL)
for line in reader:
print(*line, sep=';')
# copy everything changing the third field
for line in reader:
if line[2] == "USA":
actual_price = int(line[2])
print(actual_price)
new_price = int(actual_price) * 2
print(new_price)
for row in reader:
writer.writerow([row[0], row[1], ,new_price])
# ok, time to rename the file
os.replace('countries.tmp', 'countries.csv')
Thank you for answer

You are changing new_price at every iteration of your for loop. You should therefore be writing the row within the loop where you change the value:
with open('countries.csv', mode='r') as oldfile, open('countries.tmp', mode='w', newline='') as newfile:
reader = csv.reader(oldfile, delimiter=';', quotechar='"')
writer = csv.writer(newfile, delimiter=';', quotechar='"', quoting=csv.QUOTE_MINIMAL)
for row in reader:
price = int(row[2])
if row[1] == "USA":
price = price*2
writer.writerow([row[0], row[1], price])
os.replace('countries.tmp', 'countries.csv')

CSV created with Python is blank

This question was answered/resolved in the comments section.
I am a noob to Python and I wrote the code below thinking it would copy all the rows with "NY" as the state in the state field/column to a new csv file called "Output.csv".
import csv
f = open(r'C:\Users..\input.csv', 'r')
reader = csv.DictReader(f, delimiter=',')
output = open("C:...\Output.csv",'w')
fieldnames = ['firstScan', 'FinalScan', 'City', 'State', 'cld', 'daydiff']
writer = csv.DictWriter(output, fieldnames=fieldnames, delimiter=',')
for row in reader:
if row['State'] == 'NY':
writer.writerow(row)
Everything runs fine but the output csv is completely blank. The first tab is named "Output" but the sheet is blank. If I have it output to txt, that is blank as well. Any suggestions?

Try this instead:
import csv
with open('C:/Users/felasniper/Desktop/input.csv') as f:
reader = csv.DictReader(f, delimiter=',')
output = open("C:/Users/felasniper/Desktop/Output.csv", 'w')
fieldnames = ['firstScan', 'FinalScan', 'City', 'State', 'cld', 'daydiff']
writer = csv.DictWriter(output, fieldnames=fieldnames, delimiter=',')
for row in reader:
if row['State'] == 'NY':
writer.writerow(row)

(Simple Python) CSV input to usernames

I have a CSV file names.csv
First_name, Last_name
Mike, Hughes
James, Tango
, Stoke
Jack,
....etc
What I want is to be able to take the first letter of the First_name and the full Last_name and output it on screen as usernames but not include the people with First_name and Last_name property's empty. I'm completely stuck any help would be greatly appreciated
import csv
ifile = open('names.csv', "rb")
reader = csv.reader(ifile)
rownum = 0
for row in reader:
if rownum == 0:
header = row
else:
colnum = 0
for col in row:
print '%-8s: %s' % (header[colnum], col)
colnum += 1
rownum += 1
ifile.close()
Attempt #2
import csv
dataFile = open('names.csv','rb')
reader = csv.reader(dataFile)
next(reader, None)
for row in reader:
if (row in reader )
print (row[0])
I haven't saved many attempts because none of them have worked :S

import csv
dataFile = open('names.csv','rb')
reader = csv.reader(dataFile, delimiter=',', quoting=csv.QUOTE_NONE)
for row in reader:
if not row[0] or not row[1]:
continue
print (row[0][0] + row[1]).lower()
Or
import csv
dataFile = open('names.csv','rb')
reader = csv.reader(dataFile, delimiter=',', quoting=csv.QUOTE_NONE)
[(row[0][0] + row[1]).lower() for row in reader if
row[0] and row[1]]

Once you get the text from the .csv you can use the split() function to break up the text by the new lines. Your sample text is a little inconsistent, but if I understand you question correctly you can say
import csv
dataFile = open('names.csv','rb')
reader = csv.reader(dataFile)
reader = reader.split('\n')
for x in reader
print(reader[x])
Or if you want to break it up by commas just replace the '\n' with ','

Maybe like this
from csv import DictReader
with open('names.csv') as f:
dw = DictReader(f, skipinitialspace=True)
fullnames = filter(lambda n: n['First_name'] and n['Last_name'], dw)
for f in fullnames:
print('{}{}'.format(f['First_name'][0], f['Last_name']))
You have headings in your csv so use a DictReader and just filter out those whose with empty first or last names and display the remaining names.

How to read multiple records from a CSV file?

I have a csv file, l__cyc.csv, that contains this:
trip_id, time, O_lat, O_lng, D_lat, D_lng
130041910101,1300,51.5841153671,0.134444590094,51.5718053872,0.134878021928
130041910102,1335,51.5718053872,0.134878021928,51.5786920389,0.180940040247
130041910103,1600,51.5786920389,0.180940040247,51.5841153671,0.134444590094
130043110201,1500,51.5712712038,0.138532882664,51.5334949484,0.130489470325
130043110202,1730,51.5334949484,0.130489470325,51.5712712038,0.138532882664
And I am trying to pull out separate values, using:
with open('./l__cyc.csv', 'rU') as csvfile:
reader = csv.DictReader(csvfile)
origincoords = ['{O_lat},{O_lng}'.format(**row) for row in reader]
with open('./l__cyc.csv', 'rU') as csvfile:
reader = csv.DictReader(csvfile)
trip_id = ['{trip_id}'.format(**row) for row in reader]
with open('./l__cyc.csv', 'rU') as csvfile:
reader = csv.DictReader(csvfile)
destinationcoords = ['{D_lat},{D_lng}'.format(**row) for row in reader]
Where origincoords should be 51.5841153671, 0.134444590094,
trip_id should be 130041910101, and destinationcoords should be
51.5718053872, 0.134878021928.
However, I get a KeyError:
KeyError: 'O_lat'
Is this something simple and there's something fundamental I'm misunderstanding?

You just avoid the space between headers
trip_id,time,O_lat,O_lng,D_lat,D_lng
OR
reader = csv.DictReader(csvfile, skipinitialspace=True)

First things first, you get the key error, because the key does not exist in your dictionary.
Next, I would advise against running through the file 3 times, when you can do it a single time!
For me it worked, when I added the fieldnames to the reader.
import csv
from cStringIO import StringIO
src = """trip_id, time, O_lat, O_lng, D_lat, D_lng
130041910101,1300,51.5841153671,0.134444590094,51.5718053872,0.134878021928
130041910102,1335,51.5718053872,0.134878021928,51.5786920389,0.180940040247
130041910103,1600,51.5786920389,0.180940040247,51.5841153671,0.134444590094
130043110201,1500,51.5712712038,0.138532882664,51.5334949484,0.130489470325
130043110202,1730,51.5334949484,0.130489470325,51.5712712038,0.138532882664
"""
f = StringIO(src)
# determine the fieldnames
fieldnames= "trip_id,time,O_lat,O_lng,D_lat,D_lng".split(",")
# read the file
reader = csv.DictReader(f, fieldnames=fieldnames)
# storage
origincoords = []
trip_id = []
destinationcoords = []
# iterate the rows
for row in reader:
origincoords.append('{O_lat},{O_lng}'.format(**row))
trip_id.append('{trip_id}'.format(**row))
destinationcoords.append('{D_lat},{D_lng}'.format(**row))
# pop the header off the list
origincoords.pop(0)
trip_id.pop(0)
destinationcoords.pop(0)
# show the result
print origincoords
print trip_id
print destinationcoords
I don't really know what you are trying to achieve there, but I'm sure there is a better way of doing it!

Adding a column in csv using python

I have hundreds of .csv files with 40 rows and 34 columns each. I want to add a column at position 26 and column 26-34 should shift to make space for the new one. First row of the file is empty and second row has the titles and rest have the values. The new column should have a title in row two and rest of the rows can be zero.
Please help me with this code in python.
import csv
infilename = r'C:\Users\Sulabh Kumra\Desktop\input.csv'
outfilename = r'C:\Users\Sulabh Kumra\Desktop\output.csv'
with open(infilename, 'rb') as fp_in, open(outfilename, 'wb') as fp_out:
reader = csv.reader(fp_in, delimiter=",")
headers = next(reader) # read first row
writer = csv.writer(fp_out, delimiter=",")
writer.writerow(headers)
for row in reader:
row.append(row[2])
writer.writerow(row)

Inserting into a python list is pretty easy: some_list[2:2] = ['stuff','to','insert']
So your code would look like the following:
import csv
infilename = r'C:\Users\Sulabh Kumra\Desktop\input.csv'
outfilename = r'C:\Users\Sulabh Kumra\Desktop\output.csv'
with open(infilename, 'rb') as fp_in, open(outfilename, 'wb') as fp_out:
reader = csv.reader(fp_in, delimiter=",")
writer = csv.writer(fp_out, delimiter=",")
blank_line = next(reader)
writer.writerow(blank_line)
headers = next(reader) # read title row
headers[26:26] = ['New Label']
writer.writerow(headers)
for row in reader:
row[26:26] = [0]
writer.writerow(row)