Week 8: File I/O and CSV Processing

Course: Jan 2026 - Python Focus: Reading structured data, transforming rows, and writing safe outputs.

1. Core idea

What to remember

• Skip headers when the first line is metadata.
• line.strip().split(',') is the usual CSV pattern for this course.
• Convert numeric text to int before arithmetic.
• readline() reads one line; iterating over the file walks the rest.
• Always close files.

2. Common traps

• Forgetting the header changes the answer.
• Forgetting type conversion gives string math bugs.
• Writing filtered rows requires preserving the original row format carefully.
• The questions often ask for an average, a filtered subset, or a transformed file.

3. Speedrun pattern

1. Am I reading, filtering, aggregating, or writing?
2. Which columns are numeric?
3. Do I need the header line in the output?

4. Micro revision

• open(..., 'r') reads
• open(..., 'w') writes
• split(',') parses CSV rows
• replace() can remove or rewrite columns

Assignment anchor

• Week 8 Graded Assignment 8

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