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OPERATOR REFERENCE · PYTHON

Python Field Reference
Scripting & Automation

env → syntax → files/OS → automation → data — the scripting-for-ops slice, not the whole language

SCRIPT · .py

interpreter (CPython)

STDOUT / FILESYSTEM / NETWORK

01 Environment & Packages

◎

Virtual Environments

python -m venv .venv source .venv/bin/activate .venv\Scripts\activate # Windows

📦

Packages

pip install requests pip freeze > requirements.txt pip install -r requirements.txt

⚙

Version Management

python --version pyenv install 3.12.0 pyenv local 3.12.0

02 Core Syntax Quick Reference

Types & f-strings

name = "web01"
port: int = 8080
msg = f"{name} on {port}"

[]

Comprehensions

up = [h for h in hosts if h.ok] by_id = {h.id: h for h in hosts}

Functions

def ping(host: str, timeout: int = 5) -> bool:
    return True

⇄

Control Flow

for host in hosts:
    if not host.ok:
        continue
    print(host.name)

try / except

try:
    resp = call()
except TimeoutError as e:
    log.error(e)
finally:
    cleanup()

◈

Classes (light)

class Host:
    def __init__(self, name):
        self.name = name

03 File & OS Operations

📄

Read / Write Files

with open("out.txt") as f:
    data = f.read()

with guarantees the file handle is closed even on exception.

🗂

pathlib

from pathlib import Path
p = Path("/etc/app.conf")
p.exists()
p.read_text()

▶

subprocess

import subprocess
r = subprocess.run(
    ["systemctl", "status", "nginx"],
    capture_output=True, text=True
)

⚠ never pass shell=True with untrusted input

04 Automation Essentials

⚑

argparse

import argparse
p = argparse.ArgumentParser()
p.add_argument("--host", required=True)
args = p.parse_args()

📝

logging

import logging
logging.basicConfig(level=logging.INFO)
log = logging.getLogger(__name__)
log.info("starting run")

Prefer logging over print() in anything that runs unattended (cron, CI).

🌐

requests (HTTP)

import requests
r = requests.get(url, timeout=5)
r.raise_for_status()
data = r.json()

⚙

Environment Variables

import os
token = os.environ["API_TOKEN"]
region = os.environ.get("REGION", "us-east-1")

Prefer env vars over hardcoded secrets — pair with a .env file kept out of git.

05 Data Handling

{}

json

import json
data = json.loads(text)
json.dumps(data, indent=2)

▤

csv

import csv
with open("hosts.csv") as f:
    for row in csv.DictReader(f):
        print(row["hostname"])

re (regex)

import re
m = re.search(r"(\d+\.\d+\.\d+\.\d+)", line)
if m: ip = m.group(1)

06 Common Errors & Quick Reference

Symptom	Fix
ModuleNotFoundError	venv not activated, or pip install missing
IndentationError	mixed tabs/spaces — pick one, use 4 spaces
Script uses global site-packages unexpectedly	venv not activated before pip install
UnicodeDecodeError on file read	open(..., encoding="utf-8")
Silent failure in cron job	no logging configured — add logging.basicConfig
requests hangs forever	missing timeout= on the call

Tool	Purpose
python -m pdb script.py	debug step through interactively
python -i script.py	drop into a REPL after the script runs
pip list --outdated	see which installed packages have updates
black . / ruff check .	formatting and linting
pytest	run a test suite
deactivate	safe exit the active virtualenv