Writing a CSV file

First you need to import csv

For example:

import csv

with open('eggs.csv', 'wb') as csvfile:
    spamwriter = csv.writer(csvfile, delimiter=' ',
                        quotechar='|', quoting=csv.QUOTE_MINIMAL)
    spamwriter.writerow(['Spam'] * 5 + ['Baked Beans'])
    spamwriter.writerow(['Spam', 'Lovely Spam', 'Wonderful Spam'])

import csv
with open(fileLocation+'example.csv',newline='') as File: #the csv file is stored in a File object

    reader=csv.reader(File)       #csv.reader is used to read a file
    for row in reader:
        print(row)

To read a csv file using Pandas

use pd.read_csv("D:\sample.csv")

using only python :

fopen=open("D:\sample.csv","r") 

print(fopen.read())

To create and write into a csv file

The below example demonstrate creating and writing a csv file. to make a dynamic file writer we need to import a package import csv, then need to create an instance of the file with file reference Ex:

with open("D:sample.csv","w",newline="") as file_writer

Here if the file does not exist with the mentioned file directory then python will create a same file in the specified directory, and w represents write, if you want to read a file then replace w with r or to append to existing file then a.

newline="" specifies that it removes an extra empty row for every time you create row so to eliminate empty row we use newline="", create some field names(column names) using list like:

fields=["Names","Age","Class"]

Then apply to writer instance like:

writer=csv.DictWriter(file_writer,fieldnames=fields)

Here using Dictionary writer and assigning column names, to write column names to csv we use writer.writeheader() and to write values we use writer.writerow({"Names":"John","Age":20,"Class":"12A"}) ,while writing file values must be passed using dictionary method , here the key is column name and value is your respective key value.

Import csv:

with open("D:sample.csv","w",newline="") as file_writer:

fields=["Names","Age","Class"]

writer=csv.DictWriter(file_writer,fieldnames=fields)

writer.writeheader()

writer.writerow({"Names":"John","Age":21,"Class":"12A"})

If needed- read a csv file without using the csv module:

rows = []
with open('test.csv') as f:
    for line in f:
        # strip whitespace
        line = line.strip()
        # separate the columns
        line = line.split(',')
        # save the line for use later
        rows.append(line)

If you are working with CSV data and want a solution with a smaller footprint than pandas, you can try my package, littletable. Can be pip-installed, or just dropped in as a single .py file with your own code, so very portable and suitable for serverless apps.

Reading CSV data is as simple as calling csv_import:

data = """
1,"A towel,",1.0
42," it says, ",2.0
1337,is about the most ,-1
0,massively useful thing ,123
-2,an interstellar hitchhiker can have.,3"""

import littletable as lt
tbl = lt.Table().csv_import(data, fieldnames="number1,words,number2".split(','))
tbl.present()

Prints:

  Number1   Words                                  Number2  
 ────────────────────────────────────────────────────────── 
  1         A towel,                               1.0      
  42         it says,                              2.0      
  1337      is about the most                      -1       
  0         massively useful thing                 123      
  -2        an interstellar hitchhiker can have.   3    

(littletable uses the rich module for presenting Tables.)

littletable doesn’t automatically try to convert numeric data, so a numeric transform function is needed for the numeric columns.

def get_numeric(s):
    try:
        return int(s)
    except ValueError:
        try:
            return float(s)
        except ValueError:
            return s

tbl = lt.Table().csv_import(
    data,
    fieldnames="number1,words,number2".split(','),
    transforms={}.fromkeys("number1 number2".split(), get_numeric)
)
tbl.present()

This gives:

  Number1   Words                                  Number2  
 ────────────────────────────────────────────────────────── 
        1   A towel,                                   1.0  
       42    it says,                                  2.0  
     1337   is about the most                           -1  
        0   massively useful thing                     123  
       -2   an interstellar hitchhiker can have.         3  

The numeric columns are right-justified instead of left-justified.

littletable also has other ORM-ish features, such as indexing, joining, pivoting, and full-text search. Here is a table of statistics on the numeric columns:

tbl.stats("number1 number2".split()).present()

  Name       Mean   Min    Max   Variance              Std_Dev   Count   Missing  
 ──────────────────────────────────────────────────────────────────────────────── 
  number1   275.6    -2   1337   352390.3    593.6247130974249       5         0  
  number2    25.6    -1    123     2966.8   54.468339427597755       5         0  

or transposed:

tbl.stats("number1 number2".split(), by_field=False).present()

  Stat                 Number1              Number2 
 ─────────────────────────────────────────────────── 
  mean                   275.6                 25.6
  min                       -2                   -1
  max                     1337                  123
  variance            352390.3               2966.8
  std_dev    593.6247130974249   54.468339427597755
  count                      5                    5
  missing                    0                    0

Other formats can be output too, such as Markdown:

print(tbl.stats("number1 number2".split(), by_field=False).as_markdown())

| stat | number1 | number2 |
|---|---:|---:|
| mean | 275.6 | 25.6 |
| min | -2 | -1 |
| max | 1337 | 123 |
| variance | 352390.3 | 2966.8 |
| std_dev | 593.6247130974249 | 54.468339427597755 |
| count | 5 | 5 |
| missing | 0 | 0 |

Which would render from Markdown as

Lastly, here is a text search on the words for any entry with the word "hitchhiker":

tbl.create_search_index("words")
for match, score in tbl.search.words("hitchhiker"):
    print(match)

Prints:

namespace(number1=-2, words=’an interstellar hitchhiker can have.’, number2=3)

I wrote a question asking something similar. So, to keep everything in one place, here are my 2 cents for a very quick & dirty solution.

This code is meant to read from one CSV file and write to another. The format of the output row is fixed, I could have used csv.write with the correct delimiter, but in this case I would have to do extra work to specify the blanks. But it works nicely to show how to output text using the good old print() function:

#! /usr/bin/env python3

def main():
    parser = argparse.ArgumentParser(
        description='',
        usage="""myparser [-h] print this help and exit
        """,
        formatter_class=argparse.ArgumentDefaultsHelpFormatter
    )
    parser.add_argument('-f', '--file',help='CSV input file', required=True)
  
    args = parser.parse_args()

    with open("output.file", "w") as outfile:

        with open(args.file) as csvfile:
       
            csv_reader = csv.reader(csvfile, delimiter=',')
            line_count = 0
            for row in csv_reader:
                if line_count == 0:
                    line_count += 1
               elif args.archive:
                    print(f'no:{row[0]}:{row[1]}::0:0:0:/bin/bash:0:0:{row[2]}:{row[3]}:{row[4]}:archive', file=outfile)
                    line_count += 1 

return sys.exit(EXIT_SUCCESS)

if __name__ == '__main__':
    main()
   

Sorry for the indentation.

This code opens a CSV file for reading and uses the print() function to write a formatted string that will look like:

no:Xoero:ToelAs:xtoelas:0:0:0:/bin/bash:0:0:[email protected]:00311234567890:nl:archive