CSV Row Filter

import csv
import io

def filter_csv(csv_text: str, column: str, condition: str, value: str) -> str:
    """
    Filter CSV rows by condition on a column.
    condition: 'contains' | 'equals' | 'gt' | 'lt' | 'not_contains'
    """
    reader = csv.DictReader(io.StringIO(csv_text))
    if reader.fieldnames is None:
        return ""
    rows = []
    for row in reader:
        cell = row.get(column, "")
        if condition == "contains" and value.lower() in cell.lower():
            rows.append(row)
        elif condition == "equals" and cell == value:
            rows.append(row)
        elif condition == "not_contains" and value.lower() not in cell.lower():
            rows.append(row)
        elif condition in ("gt", "lt"):
            try:
                if condition == "gt" and float(cell) > float(value):
                    rows.append(row)
                elif condition == "lt" and float(cell) < float(value):
                    rows.append(row)
            except ValueError:
                pass

    out = io.StringIO()
    writer = csv.DictWriter(out, fieldnames=reader.fieldnames)
    writer.writeheader()
    writer.writerows(rows)
    return out.getvalue()

csv_data = """name,age,city
Alice,30,New York
Bob,25,London
Carol,35,New York"""

print(filter_csv(csv_data, "city", "equals", "New York"))
print(filter_csv(csv_data, "age", "gt", "28"))