Python and CSV files - Formula Sheet

Core CSV Methods and Parameters

This reference sheet outlines the built-in syntax, parameters, and dialects of Python's csv module.

1. Opening Files

f = open(file, mode, newline)

• file: The path string pointing to the file.
• mode: The mode parameter, such as read text ('r'), write text ('w'), append ('a'), or binary ('b').
• newline: Controls line break translation; setting newline='' prevents empty rows when writing CSVs.

2. CSV Reader Syntax

reader = csv.reader(fileobject, delimiter, fmtparams)

• fileobject: The file handler object returned by the open function.
• delimiter: The column separator character (default is a comma ',').
• fmtparams: Dialect formatting parameters such as skipinitialspace=True to trim leading white space.

3. CSV Writer Syntax

writer = csv.writer(fileobject, delimiter, fmtparams)

• fileobject: The open file handle in write or append mode.
• delimiter: The field separator character.
• fmtparams: Dialect format parameters (e.g., quoting=csv.QUOTE_ALL to wrap all fields in quotes).

4. Writing Rows

writer.writerow(row) and writer.writerows(rows)

• row: A 1D sequence (list or tuple) representing field values of a single record.
• rows: A 2D sequence containing multiple nested rows to write sequentially.

5. Dictionary Reader and Writer

d_reader = csv.DictReader(fileobject, fieldnames=None) and d_writer = csv.DictWriter(fileobject, fieldnames)

• fieldnames: A sequence of strings that serve as the dictionary keys for row mappings.
• d_writer.writeheader(): Writes a row using the defined fieldnames as headers.

6. Skipping Rows

next(reader)

• reader: The active CSV reader iterator. Moves the cursor to the next line (commonly used to skip header rows).