The File Size Profiler

A medium Python interview practice problem on DataDriven. Write the Python and run it against test cases, with instant feedback.

Domain
Python
Difficulty
medium
Seniority
L3

Problem

Given entries (list of 'filepath size_bytes timestamp' strings), sum size_bytes per file extension (everything after the last '.' in the filename). Files without an extension (no '.' in basename) are grouped under the key 'no_ext'. Extension matching is case-insensitive, so 'report.CSV' counts toward 'csv'. Return a dict mapping each lowercased extension (or 'no_ext') to the total size in bytes.

File types and their disk footprint. One type dominates.

Example

Input:

entries = ["/var/log/app.log 46080 1704067200","/var/log/error.log 1024 1704067201","/data/export.csv 102400 1704067202","/usr/bin/python3 8192 1704067203","/data/report.CSV 51200 1704067204"]

Output:

{"log":47104,"csv":153600,"no_ext":8192}

Worked solution and explanation

Why this problem exists in real interviews

This tests string parsing combined with grouping aggregation, a common log analysis pattern. It probes file path parsing, extension extraction, and case-insensitive grouping.

Break down the requirements

Step 1: Parse each metadata string

Split each entry by spaces to extract the filepath and the size. Take the basename (after the last '/'), then extract the file extension from it.

Step 2: Handle files without extensions

If no dot exists in the filename, group under 'no_ext'.

Step 3: Aggregate sizes by extension, case-insensitive

Convert extensions to lowercase before grouping, so report.CSV and export.csv both accumulate under 'csv'.

The solution

Parse, extract extension, and aggregate
def size_by_extension(entries: list[str]) -> dict[str, int]:
    totals = {}
    for entry in entries:
        parts = entry.split()
        filepath = parts[0]
        size = int(parts[1])
        filename = filepath.split('/')[-1]
        if '.' in filename:
            ext = filename.rsplit('.', 1)[1].lower()
        else:
            ext = 'no_ext'
        if ext in totals:
            totals[ext] += size
        else:
            totals[ext] = size
    return totals

Common follow-up questions