7. Files & APIs

Read and write files safely, work with paths, and call web APIs reliably.

Q1 What is the best way to read from a file?

Answer: The with open(...) statement is the standard. It automatically handles closing the file, even if errors occur. The pathlib module is a modern, object-oriented way to handle file paths.

from pathlib import Path
path = Path("data.txt")

# write
path.write_text("Hello", encoding="utf-8")

# read
with path.open("r", encoding="utf-8") as f:
    data = f.read()

Q2 How do you make an HTTP request to a web API?

Answer: The requests library is the standard for making HTTP requests. You can use it to GET data from or POST data to web services.

import requests

response = requests.get("https://api.github.com/users/python")
if response.status_code == 200:
    data = response.json() # .json() parses the JSON response

Q3 What is JSON and how do you use it in Python?

Answer: JSON is a lightweight text format for data exchange, common in web APIs. Python's built-in json module can parse JSON strings into Python dictionaries (json.loads()) and convert Python objects into JSON strings (json.dumps()).

import json

data = json.loads('{"name": "Ada", "age": 30}')
text = json.dumps(data, indent=2, ensure_ascii=False)

Q4 How do you build a simple CLI with argparse?

Answer: Use argparse.ArgumentParser to define arguments and parse them from the command line.

import argparse

parser = argparse.ArgumentParser()
parser.add_argument("name")
parser.add_argument("--times", type=int, default=1)
args = parser.parse_args(["Ada", "--times", "2"])  # example

for _ in range(args.times):
    print(f"Hello {args.name}")

Q5 How do you work with CSV files?

Answer: Use the csv module for robust parsing and writing; always open files with newline="" on Windows to avoid extra blank lines.

import csv
from pathlib import Path

with Path("data.csv").open("w", newline="", encoding="utf-8") as f:
    writer = csv.writer(f)
    writer.writerow(["name", "age"]) 
    writer.writerows([["Ada", 30], ["Bob", 25]])

with Path("data.csv").open("r", newline="", encoding="utf-8") as f:
    reader = csv.DictReader(f)
    rows = list(reader)

Q6 How to read/write binary files?

Answer: Use modes "rb" and "wb"; process bytes objects.

data = Path("image.png").read_bytes()
Path("copy.png").write_bytes(data)

Q7 How to make HTTP requests robustly?

Answer: Always set timeouts, handle exceptions, and consider retries/backoff.

import requests

try:
    resp = requests.get("https://example.com", timeout=5)
    resp.raise_for_status()
except requests.exceptions.RequestException as e:
    print("Request failed:", e)

Q8 How do you work with paths using pathlib?

Answer: Use Path methods like joinpath, glob, and iterdir for cross-platform path handling.

from pathlib import Path
logs_dir = Path("logs")
for p in logs_dir.glob("*.log"):
    print(p.name)