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Week 3 Checkpoint: Functions, Files, and JSON — Python For Freelancers

Week 3 Checkpoint: Functions, Files, and JSON — Python For Freelancers | zuzu.codes

Day 22 · ~11 min●

Five functions, all connecting to the pipeline you started in Week 1. Which one felt most different from what you expected?

load_clients_from_csv with io.StringIO. I expected file reading to involve opening a file path. A fake-file wrapper for a string feels like a workaround.

It is a design choice, not a workaround. The function signature takes a string — testable, composable, and identical whether the string came from disk, an API, or your time-tracker export. The StringIO wrapper is the adapter between string and file interface.

clients_to_json was the most satisfying. The round-trip test — dumps, loads, verify — made the output feel solid. Not just a formatted string; an actually validated JSON blob.

That instinct for verification is worth more than any single function. Let's see what the full three weeks have built.

Ready. Six questions from the full pipeline.

Two from Weeks 1 and 2 to keep those patterns warm.

Quiz

0/6

6 questions80% to passretry anytime

1.What does make_invoice_line('Acme Corp', {'total_hours': 4.5, 'total_revenue': 540.0, 'avg_rate': 120.0}, 1) return?

def make_invoice_line(name, stats, rank):
    hours = stats.get('total_hours', 0)
    revenue = stats.get('total_revenue', 0.0)
    rate = stats.get('avg_rate', 0.0)
    return f"#{rank} {name} — Hours: {hours:.1f} | Rate: ${rate:.2f}/hr | Total: ${revenue:.2f}"

2.What does summarize_client([{'name': 'Acme', 'rate': 120.0, 'hours': 4.5}], 'Ghost') return?

(4.5, 540.0, 120.0)(0, 0.0, 0.0)KeyError: 'Ghost'[]

3.Why does load_clients_from_csv use io.StringIO(csv_text) instead of passing csv_text directly to csv.DictReader?

io.StringIO converts the string encoding to UTF-8 firstcsv.DictReader expects a file-like object that supports iteration line by line — io.StringIO wraps the string in that interfacecsv.DictReader cannot read strings with commas without the StringIO wrapperio.StringIO buffers the string in memory for faster parsing on large files

4.What is the difference between json.dumps and json.loads?

dumps writes JSON to disk; loads reads it back from diskdumps converts a Python object to a JSON string; loads converts a JSON string back to a Python objectdumps validates JSON syntax; loads parses validated JSON into Pythondumps and loads are identical — both produce JSON strings

5.[REVIEW] group_by_status from Week 2 accumulates clients into a dict keyed by status. What does it return for a client list where all clients have status: 'on track'?

{'on track': [... all clients ...]}[... all clients ...]{'on track': len(clients)}{}

6.[REVIEW] What does categorize_project_status(5.4, 5.0) return, from Week 1?

def categorize_project_status(actual, budgeted):
    if actual < budgeted * 1.1:
        return "on track"
    elif actual < budgeted * 1.25:
        return "over by 10%"
    else:
        return "critical"

"on track""over by 10%""critical"True