list2csv 1.3.6

A simple package intended to help write iterables of objects to CSV files

List2CSV

List2CSV is a simple package that helps with writing lists of objects to CSV files.

Installation

list2csv can be downloaded from pypi or installed using pip:

pip install list2csv

Usage

List2CSV exposes a Writer class that manages CSV columns and writing to a TextIO stream. Columns are first configured on a Writer instance before data is written in CSV format to the stream.

The following examples will use this Student class and list to demonstrate usage.

from dataclasses import dataclass
from statistics import mean


@dataclass
class Student:
    student_id: str
    test_1_mark: float
    test_2_mark: float
    assignment_marks: list[float]
    lab_marks: list[float]
    comments: list[str]

    @property
    def grade(self):
        return (
                60 * mean((self.test_1_mark, self.test_2_mark))
                + 30 * mean(self.assignment_marks)
                + 10 * mean(self.lab_marks)
        ) / 100


students = [
    Student('abcd123',
            78.5, 88,
            [84.5, 96, 87],
            [92.3, 98, 100, 70],
            ['Good', 'Needs work on classes']),
    Student('efgh456',
            62, 74,
            [70.5, 76, 80],
            [98, 68.2, 0, 93.5],
            ['Good', 'Needs work on formatting', 'Needs work on recursion']),
    Student('ijkl789',
            100, 99.5,
            [98.5, 100, 100],
            [100, 100, 98.7, 100],
            ['Excellent']),
]

Adding Columns

The most basic column configuration is to use the add_column method to add a column with a name and a function that returns the value for that column.

Column data can be formatted with an optional format string to specify how data should be formatted as it is written to the CSV file.

import list2csv

with open('grades.csv') as f:
    writer = list2csv.Writer(f)
    writer.add_column('ID', lambda s: s.student_id)

    writer.write_header()
    writer.write_all(students)

Which will produce the following table:

ID
abcd123
efgh456
ijkl789

However, instead of a function, lambda s: s.student_id, you can also use a string of the attribute name of the objects being written:

import list2csv

with open('grades.csv', 'w', newline='') as f:
    writer = list2csv.Writer(f)
    writer.add_column('ID', 'student_id')

    writer.write_header()
    writer.write_all(students)

Would produce the same table as before.

Several columns can be added with subsequent calls to add_column.

import list2csv

with open('grades.csv', 'w', newline='') as f:
    writer = list2csv.Writer(f)
    writer.add_column('ID', 'student_id')
    writer.add_column('Test 1', 'test_1_mark', '{:.2f}')
    writer.add_column('Test 2', 'test_2_mark', '{:.2f}')

    writer.write_header()
    writer.write_all(students)

Would produce the following table:

ID	Test 1	Test 2
abcd123	78.5	88
efgh456	62	74
ijkl789	100	99.5

Counters

Counter columns can be added which increment by a given step value for each row written to the CSV. Counter columns have a default start value of 1 and a default step value of 1.

with open('grades.csv', 'w', newline='') as f:
    writer = list2csv.Writer(f)
    writer.add_counter('Student Num')
    writer.add_column('ID', 'student_id')
    writer.add_column('Test 1', 'test_1_mark', '{:.2f}')
    writer.add_column('Test 2', 'test_2_mark', '{:.2f}')

    writer.write_header()
    writer.write_all(students)

Which would produce the following table:

Student Num	ID	Test 1	Test 2
1	abcd123	78.5	88
2	efgh456	62	74
3	ijkl789	100	99.5

Any number of counters with separate start and step values can be added to the same CSV file.

Multi Columns

It is often desirable to write iterables of data to separate columns of a CSV file. in such cases, a multi_column can be added to the Writer instance.

Multi columns take a headder_formatter as opposed to a header name. Each resulting column will be named header_template.format(i), where i is the one-based index of the column.

Multi columns will also need to be defined with the number of columns that will be added.

with open('grades.csv', 'w', newline='') as f:
    writer = list2csv.Writer(f)
    writer.add_counter('Student Num')
    writer.add_column('ID', 'student_id')
    writer.add_column('Test 1', 'test_1_mark', '{:.2f}')
    writer.add_column('Test 2', 'test_2_mark', '{:.2f}')
    writer.add_multi('Assignment {}', 'assignment_marks', 3, '{:.2f}')

    writer.write_header()
    writer.write_all(students)

Would produce the following table:

Student Num	ID	Test 1	Test 2	Assignment 1	Assignment 2	Assignment 3
1	abcd123	78.50	88.00	84.50	96.00	87.00
2	efgh456	62.00	74.00	70.50	76.00	80.00
3	ijkl789	100.00	99.50	98.50	100.00	100.00

Aggregator Columns

Aggregator columns can collate the data from several columns into a single column. Each column can be added with a set of aggregator IDs. When aggregator columns are added with an ID, all columns with a matching ID will be aggregated into a single column using an aggregator function. For example:

with open('grades.csv', 'w', newline='') as f:
    writer = list2csv.Writer(f)
    writer.add_counter('Student Num')
    writer.add_column('ID', 'student_id')
    writer.add_column('Test 1', 'test_1_mark', '{:.2f}', {'test'})
    writer.add_column('Test 2', 'test_2_mark', '{:.2f}', {'test'})
    writer.add_aggregator('test', 'Av Test Mark', mean, '{:.2f}')
    writer.add_multi(
        'Assignment {}', 'assignment_marks', 3, '{:.2f}', {'assignment'}
    )
    writer.add_aggregator('assignment', 'Av Assignment Mark', mean, '{:.2f}')

    writer.write_header()
    writer.write_all(students)

Would produce the following table:

Student Num	ID	Test 1	Test 2	Av Test Mark	Assignment 1	Assignment 2	Assignment 3	Av Assignment Mark
1	abcd123	78.50	88.00	83.25	84.50	96.00	87.00	89.17
2	efgh456	62.00	74.00	68.00	70.50	76.00	80.00	75.50
3	ijkl789	100.00	99.50	99.75	98.50	100.00	100.00	99.50

While aggregator columns may be useful for aggregating data from multiple attributes, in the case of aggregating multi columns it may just be more useful to add a single column with an aggregating function. For example:

    ...
    writer.add_multi('Assignment {}', 'assignment_marks', 3, '{:.2f}')
    writer.add_column(
        'Av Assignment Mark', lambda s: mean(s.assignment_marks), '{:.2f}'
    )
    ...

Extended Example

with open('grades.csv', 'w', newline='') as f:
    writer = list2csv.Writer(f)
    writer.add_counter('Student Num')
    writer.add_column('ID', 'student_id')
    writer.add_column('Test 1', 'test_1_mark', '{:.2f}', {'test'})
    writer.add_column('Test 2', 'test_2_mark', '{:.2f}', {'test'})
    writer.add_aggregator('test', 'Av Test Mark', mean, '{:.2f}')
    writer.add_multi(
        'Assignment {}', 'assignment_marks', 3, '{:.2f}', {'assignment'}
    )
    writer.add_aggregator('assignment', 'Av Assignment Mark', mean, '{:.2f}')
    writer.add_multi('Lab {}', 'lab_marks', 4, '{:.2f}', {'lab'})
    writer.add_aggregator('lab', 'Av. Lab Mark', mean, '{:.2f}')
    writer.add_column('Grade', 'grade', '{:.2f}')
    writer.add_column('Comments', lambda s: '\n'.join(s.comments))

    writer.write_header()
    writer.write_all(students)

Student Num	ID	Test 1	Test 2	Av Test Mark	Assignment 1	Assignment 2	Assignment 3	Av Assignment Mark	Lab 1	Lab 2	Lab 3	Lab 4	Av. Lab Mark	Grade	Comments
1	abcd123	78.50	88.00	83.25	84.50	96.00	87.00	89.17	92.30	98.00	100.00	70.00	90.08	85.71	Good Needs work on classes
2	efgh456	62.00	74.00	68.00	70.50	76.00	80.00	75.50	98.00	68.20	0.00	93.50	64.92	69.94	Good Needs work on formatting Needs work on recursion
3	ijkl789	100.00	99.50	99.75	98.50	100.00	100.00	99.50	100.00	100.00	98.70	100.00	99.67	99.67	Excellent

Note

Files should be opened with newline='' to allow for universal newline support.