How to Automate Gym Reservations with Selenium: A Google‑Style Design Doc

Problem Description

During the COVID‑19 pandemic gyms required members to pre‑book slots two days in advance, opening at midnight. The author needed a way to secure a 6 am slot without staying up late.

Requirements

Automatically book a gym slot two days ahead at midnight.

Run without human interaction, be fault‑tolerant and retry intelligently.

Run on macOS.

Allow user to specify username, password, sport, date, time, and other parameters.

Out of scope:

Booking only 1‑2 days ahead or same‑day.

Tolerating OS or network failures.

Operating after the booking server stops.

Working after the website HTML structure changes.

Overview Design

Comparison of browser automation vs. simulated HTTP requests. Browser automation was chosen because it runs a real browser, making debugging easier and handling JavaScript‑rendered controls, even though it depends on the page’s HTML structure.

The implementation uses Python, Selenium (Firefox + GeckoDriver), and the macOS caffeinate utility to prevent sleep.

Detailed Design

User Input

Username, password, date, etc. are supplied via command‑line arguments.

Retry Logic

The program catches all exceptions and retries up to 100 times until the booking succeeds, identified by confirming a specific DOM element.

Browser Choice

Firefox was selected after testing Chrome and Safari, which required extra driver steps.

Logging

Each loop logs what action was performed and what it is waiting for, facilitating debugging.

Preventing Sleep

The macOS caffeinate tool is launched as a subprocess to keep the computer awake until midnight:

subprocess.Popen(['caffeinate', '-d', '-w', '%d' % os.getpid()])

Element Location

Selenium’s find_element_by_xpath is used with robust text‑based locators to find buttons, inputs, and other controls.

Waiting for Page Load

The WebDriverWait API waits up to 120 seconds for the appointment button to become clickable:

book_btn = WebDriverWait(driver, 120).until(EC.element_to_be_clickable((By.XPATH, "//button[@ng-reflect-router-link='/Appointments']")))

Additional Details

Logic handles month selection, date‑cell identification, and edge cases when the target date falls in the next month.

Operation Flow

Run the script the day before the desired slot, for example:

python book.py --username xxxx --password xxxx --day 14 --time '5:00 PM' --sport small_pool

The script wakes every second, uses caffeinate to keep the Mac awake until midnight, launches Firefox, completes the booking, then exits. After execution the system can sleep normally.

Booking is highly competitive; only six slots per time slot are available and they fill within the first minute.

Relevant links:

https://github.com/luanjunyi/smac_booking_robot

https://docs.google.com/document/d/1NRj-NdDW_wD1-GwZAJc-Nfrbq8xMiX1Hggrzguh-fjY/edit?usp=sharing

https://www.selenium.dev/

https://ss64.com/osx/caffeinate.html

https://selenium-python.readthedocs.io/locating-elements.html

https://selenium-python.readthedocs.io/waits.html?highlight=WebDriverWait#explicit-waits