Python handles CSV two

The above document describes the reading and writing of CSV and the basics

Python processes CSV files

CSV is a bit more complicated

There is such a CSV file with the following contents: Name, Department, Birthday, Month, 4 fields

name,department,birthday month
John Smith,Accounting,November
Erica Meyers,IT,March           

After reading this file, I want to customize the output

import csv

with open('employee_birthday.txt', mode='r') as csv_file:
    csv_reader = csv.DictReader(csv_file)
    line_count = 0
    for row in csv_reader:
        if line_count == 0:
            print(f'Column names are {", ".join(row)}')
            line_count += 1
        print(f'\t{row["name"]} works in the {row["department"]} department, and was born in {row["birthday month"]}.')
        line_count += 1
    print(f'Processed {line_count} lines.')           

Column names are name, department, birthday month
    John Smith works in the Accounting department, and was born in November.
    Erica Meyers works in the IT department, and was born in March.
Processed 3 lines.           

Complex example of writing SSV

import csv

with open('employee_file.csv', mode='w') as employee_file:
    employee_writer = csv.writer(employee_file, delimiter=',', quotechar='"', quoting=csv.QUOTE_MINIMAL)

    employee_writer.writerow(['John Smith', 'Accounting', 'November'])
    employee_writer.writerow(['Erica Meyers', 'IT', 'March'])           

employee_writer = csv.writer(employee_file, 
delimiter=',', 
                             quotechar='"', 
                             quoting=csv.QUOTE_MINIMAL)           

• .csv. QUOTE_MINIMA Reference those fields that contain special characters, such as delimiters, quotation mark characters, or characters in any line terminator.
• The default delimiter is comma-separated

employee_writer.writerow(['John Smith', 'Accounting', ',November'])           

, November This value contains a comma

If you look at the effect after writing to the file, the whole string is wrapped in quotation marks, which is also one of the standards for CSV.

• John Smith,Accounting,",November"

The header is written in the first row of the CSV file

We know that usually the first one in CSV will give a header row that indicates the meaning of the data in each row, but of course this is not necessary. Just look at the needs of the business

import csv

with open('employee_file2.csv', mode='w') as csv_file:
    fieldnames = ['emp_name', 'dept', 'birth_month']
    writer = csv.DictWriter(csv_file, fieldnames=fieldnames)

    writer.writeheader()
    writer.writerow({'emp_name': 'John Smith', 'dept': 'Accounting', 'birth_month': 'November'})
    writer.writerow({'emp_name': 'Erica Meyers', 'dept': 'IT', 'birth_month': 'March'})           

Take a look at the file after writing

Use a more wintery tool, pandas, to handle CSV

import pandas
df = pandas.read_csv('hrdata.csv')
print(df)           

emp_name        dept birth_month
0    John Smith  Accounting    November
1  Erica Meyers          IT       March