使用 Python 将列添加到现有的 CSV 文件

Question

I'm trying to add a new column header and values to an existing csv file with python. Every thing I've looked up appends the header to the last row of the last column. This is what I want my results to be essentially.

Header Header2 Header3 NewHeader Value Value2 Value3 NewValue

What I'm currently getting is this:

Header   Header2   Header3
Value    Value2    Value3**NewHeader
NewValue`

This is my code:

import csv
  with open('filename.csv', 'a') as csvfile:
  fieldnames = ['pageviewid']
  writer = csv.DictWriter(csvfile, fieldnames=fieldnames)

  writer.writeheader()
  writer.writerow({'pageviewid': 'Baked'})
  writer.writerow({'pageviewid': 'Lovely'})
  writer.writerow({'pageviewid': 'Wonderful'})

Answer 1

If using pandas is an option:

import pandas as pd
df = pd.read_csv('filename.csv')
new_column = pd.DataFrame({'new_header': ['new_value_1', 'new_value_2', 'new_value_3']})
df = df.merge(new_column, left_index = True, right_index = True)
df.to_csv('filename.csv', index = False)

Answer 2

Easiest way would be to rewrite to an output file

import csv
reader = csv.reader(open('filename.csv', 'r'))
writer = csv.writer(open('output.csv', 'w'))
headers = reader.next()
headers.append("Brand New Awesome Header")
writer.writerow(headers)
for row in reader:
    row.append(new data for my new header)
    writer.writerow(row)