app.py

import json

from flask import Flask, request, url_for, jsonify

app = Flask(__name__)

with open('photos.json') as fp:
    PHOTOS = json.loads(fp.read())

with open('albums.json') as fp:
    ALBUMS = json.loads(fp.read())

@app.route("/")
def index():
    return jsonify({
        'albums_url': url_for('albums', _external=True),
        'photos_url': url_for('photos', _external=True)
    })


def find_photo(photo_id):
    return next(photo for photo in PHOTOS if photo['id'] == photo_id)

def _get(collection, _id=None):
    return jsonify(
        next(obj for obj in collection if obj['id'] == int(_id)) if _id else
        collection
    )

@app.route("/albums", methods=['GET', 'POST'])
@app.route("/albums/<album_id>")
def albums(album_id=None):
    if request.method == 'POST':
        album_data = request.get_json()
        album_data['id'] = max([album['id'] for album in ALBUMS]) + 1
        ALBUMS.append(album_data)
        return jsonify(album_data)
    else:
        return _get(ALBUMS, album_id)

@app.route("/photos")
@app.route("/photos/<photo_id>")
def photos(photo_id=None):
    return _get(PHOTOS, photo_id)

@app.route("/albums/<album_id>/photos", methods=['GET', 'POST'])
def album_photos(album_id):
    if request.method == 'POST':
        photo_id = request.get_json()['id']
        photo_data = dict(find_photo(photo_id))
        photo_data['albumId'] = int(album_id)
        PHOTOS.append(photo_data)
        return jsonify(photo_data)
    photos = [photo for photo in PHOTOS if photo['albumId'] == int(album_id)]
    return jsonify(photos)

if __name__ == "__main__":
    app.run(debug=True)