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Selenium入門

ブラウザー自動化とJavaScriptでレンダリングされるコンテンツのスクレイピングに使える強力なツール、Seleniumを始めます。

「Selenium入門」はCoddyKit上の無料Web Scraping & Botsレッスンです。 これはレッスン1/4です。 下記で完全なレッスンを無料で読むことができます。その後、ブラウザ内の組み込みコードエディタと24時間対応のAIチューターでハンズオン演習できます。 これはWeb Scraping & Bots学習パスの一部であり、ウェブとCoddyKitアプリ全体で進捗が同期されます。 Web Scraping & Botsコースには全4レッスンが含まれています。

このレッスンの一部はまだ翻訳されておらず、英語で表示されています。

Dynamic Content Challenge

Most websites today aren't static pages. They use JavaScript to load content after the initial page renders.

Think of social media feeds, search results that update as you scroll, or interactive forms. Traditional scraping tools (like Requests) often miss this content because they only fetch the initial HTML.

Meet Selenium WebDriver

Selenium WebDriver is a powerful tool designed to automate web browsers. Unlike libraries that just fetch HTML, Selenium actually launches a real browser (like Chrome or Firefox).

This means it can execute JavaScript, interact with elements, and see the web page exactly as a human user would, making it perfect for dynamic content.

Selenium's Core Idea

Selenium works by sending commands to a specific browser driver (e.g., ChromeDriver for Chrome, GeckoDriver for Firefox).

  • Your Python script tells the driver what actions to perform.
  • The driver then controls the actual browser.
  • The browser executes these actions (navigating, clicking, typing) and returns the updated page state or data.

Install Selenium Library

First, let's install the Selenium library for Python. You can do this using pip, Python's package installer.

Open your terminal or command prompt and run:

pip install selenium

This command downloads and installs the necessary Python components to interact with browsers.

Get Your Browser Driver

Selenium needs a specific browser driver to control your browser. For Chrome, you'll need ChromeDriver. For Firefox, it's GeckoDriver.

1. Check your browser version (e.g., Chrome -> Help -> About Google Chrome).

2. Download the matching driver from its official site:

Place the downloaded driver executable (e.g., chromedriver.exe) in a location accessible by your system's PATH, or note its full path.

Launch Your First Browser

Let's write our first script to open a Chrome browser window using Selenium WebDriver.

Make sure your chromedriver is accessible (either in your PATH or specify its path directly in the Service object).

from selenium import webdriver
from selenium.webdriver.chrome.service import Service
import time

def main():
    driver = None
    try:
        # IMPORTANT: Ensure ChromeDriver is installed and in your system PATH.
        # If not, specify its path directly:
        # service = Service("/path/to/your/chromedriver") 
        # driver = webdriver.Chrome(service=service)
        
        driver = webdriver.Chrome() # Assumes chromedriver is in PATH
        print("Chrome browser launched successfully!")
        
        time.sleep(5) # Keep browser open for 5 seconds to observe
        
    except Exception as e:
        print(f"An error occurred: {e}")
    finally:
        if driver:
            driver.quit() # Always close the browser
            print("Browser closed.")

if __name__ == "__main__":
    main()

Go to a Web Page

Once the browser is open, you can tell it to navigate to any URL using the .get() method.

This is like typing a URL into the address bar and pressing Enter. The browser will load the page, including any JavaScript content.

from selenium import webdriver
import time

def main():
    driver = None
    try:
        driver = webdriver.Chrome() 
        print("Browser launched.")
        
        print("Navigating to example.com...")
        driver.get("https://www.example.com") 
        
        print(f"Current page title: {driver.title}")
        print(f"Current URL: {driver.current_url}")
        
        time.sleep(5) # Keep browser open to see the page
        
    except Exception as e:
        print(f"An error occurred: {e}")
    finally:
        if driver:
            driver.quit()
            print("Browser closed.")

if __name__ == "__main__":
    main()

Waiting for Content

Web pages often take time to load completely, especially with dynamic content. Selenium provides ways to wait for elements to appear.

For now, we'll use a simple time.sleep() to pause execution. Later lessons will cover more robust explicit and implicit waits, which are more efficient.

  • time.sleep(seconds): Pauses execution for a fixed duration.

Always Close Your Browser

It's crucial to close the browser window when your script is done. This frees up system resources and prevents lingering browser processes.

Use the .quit() method on your WebDriver instance. This closes the browser and ends the WebDriver session cleanly.

from selenium import webdriver
import time

def main():
    driver = None
    try:
        driver = webdriver.Chrome() 
        print("Browser launched.")
        
        driver.get("https://www.example.com") 
        print(f"Navigated to: {driver.current_url}")
        
        time.sleep(3) # Wait a bit to see the page
        
    except Exception as e:
        print(f"An error occurred: {e}")
    finally:
        if driver:
            driver.quit() # This line closes the browser window
            print("Browser closed successfully!")

if __name__ == "__main__":
    main()

Quick Check

You've launched your first browser with Selenium! What is the primary purpose of using Selenium WebDriver compared to libraries like Requests for web scraping?

Recap & Next Steps

In this lesson, you learned:

  • Why Selenium is essential for handling dynamic web content.
  • How to install the Selenium library and obtain a browser driver.
  • To launch a browser, navigate to a URL, and close the session cleanly.

Next, we'll dive deeper into automating browser interactions like clicks, form submissions, and finding specific elements on a page!

よくある質問

「Selenium入門」レッスンは無料ですか？

はい。「Selenium入門」の完全なテキストはこのウェブで無料で読めます。インタラクティブに演習し（組み込みコードエディタと24時間対応のAIチューター）、Web Scraping & Botsコースの残りをアンロックするには、CoddyKit PROにアップグレードしてください。 Web Scraping & Botsコースには全4レッスンが含まれています。

「Selenium入門」で何を学びますか？

ブラウザー自動化とJavaScriptでレンダリングされるコンテンツのスクレイピングに使える強力なツール、Seleniumを始めます。 ブラウザで直接実行するハンズオンコードでWeb Scraping & Botsを演習し、24時間対応のAIチューターがレッスンを進める中での質問に答えます。

Web Scraping & Botsを始めるのに経験は必要ですか？

事前経験は必要ありません。CoddyKitのWeb Scraping & Botsは初級者から上級者向けに構成されているため、ここから始めるか最初から始めて、自分のペースで進むことができます。 これはレッスン1/4です。

「Selenium入門」レッスンにはどのくらい時間がかかりますか？

ほとんどのCoddyKitレッスンは約5～10分かかります。各レッスンはコンパクトでインタラクティブなので、着実に進歩し、ウェブとアプリ全体で正確に前回の場所から再開できます。

このWeb Scraping & Botsレッスンでコードを書いて実行できますか？

はい。すべてのWeb Scraping & Botsレッスンに組み込みコードエディタが含まれているため、ブラウザでリアルコードを書いて実行し、即座のAIフィードバックを取得できます。ローカル設定は不要です。

このコースのすべてのレッスン

  1. Selenium入門
  2. ブラウザー操作の自動化
  3. JavaScriptからのデータ抽出
  4. 動的ページの待機戦略
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