CSV (,)

• (docs)[https://docs.python.org/3.12/library/csv.html#module-csv]

• stands for Comma Seperated Values
• structured data format soted as a plain text file
• commonly used to exchange speadsheets and database files

’'’csv model, releasedate,memory, CPU PC, 08-1981, 8080 (…/) ‘’’

CSV Structure

• Header (first line in a CSV file, metadata)
• Rows (data itself, each row represents a record, devided by delimiter)
• columns (each column repesents a field, devided by delimiter)
• Delimiters (can be any character)

Reading CSV files

1. import csv module
2. open a file object for reading
3. open CSV reader object (accepts a file object as an argument)
4. iterate CSV reader object (a row at a time)
5. close the file object (not needed when using context manager)

import csv
csv.reader(csvfile)

• return a CSV reader object from the file object csvfile
• CSV reader object is also an iterator (put it in a for loop or convert it to a list) => file object is an iterator as well
• at each iteration it returns a row
• each row is a list of strings
• each string corresponds to a CSV column

import csv
with open ('ibmpcs.csv') as f:
    # if the mode is not specified, default is read
    rows = list(csv.reader(f))
    # creating a reader object by passing it the file object f
    # convert the iterator to list
    # set the variable rows to it
    header = rows[0]
    # first item in rows is the header
    print(f'{header[1]}\t{header[0]}')

    for row in rows[1:]:
        print(f'{row[1]}\t\t{row[0]}')
        # iteratign through the remaining rows
        # we will set the variable row to each row from the file
        # we skip the first row sinc ethat is our header: using a slice starting at index 1till the end of the list

• index 1 is release date field, index zero is the model field

Writing to CSV files

1. import csv module
2. open file object for writing
3. open a CSV writer object
4. Pass the file object to it
5. Call write methods in the CSV writer object (this will write our data to the file)
6. Close file object (skip that when using the context manager)

import csv
csv.writer(csvfile)

• return a CSV writer object from

import csv
csvwriter.writerow(row)

• write row to the writer’s file object
• row is a container, a list of items, converted to string before written
• all items in row converted to strings before writing
• write all items in a rows to the writer’s file object
• rows is a container of containers

import csv
header = ['ID', 'Name', 'Rank']
# setting up the header
data = [
    [1, 'Picard', 'Captain'],
    [2, 'Crisher', 'Commander'],
    [3, 'La Forge', 'Lt. Cmdr.'],
]
# a list of lists

with open ('starfleet.csv', 'w') as f:
    cw = csv.writer(f)
    # create a CSV file writer object
    # we pass it the file object f
    cw.writerow(header)
    # writes one row, the header, to the CSV file
    cw.writerows(data)
    # we don't need to convert the ID integer

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	Strings		Variables		Lists		Tuples		Dictionary
	Control		Function		Files		Exceptions
	OOP		Algorithm		Data Structure		back

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