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Week 8: File I/O and CSV Processing

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

1. Core idea

Week 8 turns Python into a file processor: open, read, parse, transform, write, close.

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

When you see a Week 8 question, ask:
  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

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