9.16 Hands-on Exercises

Log Level Analyzer

Build a function that scans a batch of log lines and tallies how many fall into each severity level — an at-a-glance health summary without opening a log viewer.

import re
from collections import Counter

def analyze_log_levels(lines):
    levels = [re.search(r"\b(INFO|WARNING|ERROR)\b", l).group(1) for l in lines]
    return dict(Counter(levels))

>>> analyze_log_levels([
...     "2026-07-13 10:00:01 INFO Service started",
...     "2026-07-13 10:00:05 ERROR Connection refused",
...     "2026-07-13 10:00:07 WARNING High memory usage",
... ])
{'INFO': 1, 'ERROR': 1, 'WARNING': 1}

IP Address Extractor

Pull every IPv4 address out of free-form text — the first step in building a blocklist, an allowlist audit, or a geo-lookup report from security logs.

>>> text = "Connections from 192.168.1.10 and 10.0.0.5 were blocked; 8.8.8.8 allowed"
>>> re.findall(r"\b(?:\d{1,3}\.){3}\d{1,3}\b", text)
['192.168.1.10', '10.0.0.5', '8.8.8.8']

Configuration File Parser

Read a simple key=value config format, with comment lines starting with # — a recurring task for any tool that needs its own settings file without pulling in a full config-parsing library.

def parse_config(text):
    result = {}
    for line in text.splitlines():
        line = line.strip()
        if not line or line.startswith("#"):
            continue
        key, _, value = line.partition("=")
        result[key] = value
    return result

>>> parse_config("# config\nhost=localhost\nport=8080\n\ndebug=true")
{'host': 'localhost', 'port': '8080', 'debug': 'true'}

Password Strength Checker

Enforce a minimum length plus a mix of character classes — a standard first line of defense against weak passwords during account signup.

def is_strong_password(pw):
    if len(pw) < 8:
        return False
    has_upper = any(c.isupper() for c in pw)
    has_lower = any(c.islower() for c in pw)
    has_digit = any(c.isdigit() for c in pw)
    has_special = any(not c.isalnum() for c in pw)
    return all([has_upper, has_lower, has_digit, has_special])

>>> is_strong_password("Weak1")
False
>>> is_strong_password("Str0ng!Pass")
True

Mini Projects

• DevOps health report generator — turn raw HTTP status-code counts into a single human-readable error-rate line ("1000 requests, 2.0% error rate"), reusing Counter from earlier in this chapter.
• CI/CD build summarizer — parse a Jenkins-style console line ("Build #42 SUCCESS in 3m 15s") into a structured {"build", "status", "duration"} result, ready to feed a Slack notification.
• Kubernetes log analyzer — combine the pod-name parser from 9.12 Strings in DevOps and AWS with the log-level counter above to produce a per-deployment error-rate summary.

Quick Interview Answer

“These exercises tie the chapter’s tools together: the log analyzer combines regex extraction with Counter; the IP extractor is a single well-chosen regex; the config parser leans on partition() instead of a fragile manual split; and the password checker chains several is* validation methods with any(). The common thread is picking the right existing tool — regex, Counter, partition, is* — over hand-rolled character-by-character logic.”

Common Mistakes

• Using split("=") instead of partition("=") in the config parser — split() breaks on a value that itself contains an = character, while partition() splits only on the first occurrence.
• Forgetting the password checker’s has_special check needs not c.isalnum(), not a hardcoded set of symbols, so it correctly accepts any real special character.
• Letting one malformed log line crash the whole analyzer instead of skipping or flagging lines that don’t match the expected pattern (re.search(...) returning None).