Python Web Crawler

Web Crawler Requirements

Prepare to build a Python web crawler with Python 3, an IDE, course files, and reliable internet connectivity.

Why These Requirements Matter

A web crawler is software that visits web resources programmatically. A basic crawler requests a page, receives its content, identifies links or other data, and may continue by requesting additional pages.

That workflow requires three essentials: a Python runtime to execute the crawler, a place to write and run source code, and network access to contact remote web servers. This checklist prepares you for the rest of the course, including sending requests, parsing HTML, extracting links, and managing pages to visit.

Setup checklist

Install Python 3.x

Python 3.x is the supported major version family for the crawler code. The tutorial uses Python 3 syntax and behavior, so install a current Python 3 release from the official Python download site.

Earlier Python generations, such as Python 2, are not compatible with the provided code. Having Python installed is not enough if your terminal or IDE selects an older interpreter.

Verify the Python interpreter

A Python interpreter is the program that executes Python source files. Use the command appropriate for your operating system:

py --version

On Windows, the expected result begins with Python 3.

python3 --version

On macOS or Linux, the expected result also begins with Python 3. A version check confirms which interpreter a terminal command selects; it does not automatically configure every IDE project.

Run a Python file

Once Python 3 is available, a Python file can be started from a macOS or Linux terminal with:

python3 crawler.py

The script should start with the Python 3 interpreter. Its exact output depends on the lesson code. On Windows, use the Python launcher or the command configured for your Python 3 installation.

Choose an Editor or IDE

You need an environment where you can create, save, edit, organize, and execute Python files. An IDE, or integrated development environment, combines these activities in one application.

PyCharm Community Edition

PyCharm Community Edition is the primary suggested IDE for this course. It is a free, Python-focused IDE that can create projects, organize files, and run code with a configured interpreter.

1. Install PyCharm Community Edition.
2. Create or open a project for the crawler exercises.
3. Open the project interpreter settings.
4. Select or add the installed Python 3 interpreter.
5. Create or open a Python file and run a simple test script.

In the project settings, select the installed Python 3 interpreter rather than an earlier Python interpreter. The IDE may otherwise report errors or run the file with an unsupported version.

IDLE

IDLE is a basic integrated development environment commonly included with Python installations. It can open, edit, save, and run Python files, making it suitable for learners who want a lightweight option.

Whichever tool you select, confirm that it uses the same Python 3 installation that you verified in the terminal.

Internet Connectivity

An active internet connection is necessary when the crawler requests web pages. You can write and edit crawler code offline, but the crawler cannot successfully fetch remote content without network access.

A crawl can also depend on more than a general connection. Connectivity, DNS access, the accuracy of the target URL, and the target site's availability or access rules all affect whether a request succeeds.

1. Connect to the internet.
2. Open the target website in a browser to confirm that the address is reachable.
3. Run the crawler and check whether it can make a request to the target address.

Use the Course Source Code

The course code is provided as a downloadable package. Downloading it is optional if you are following along by creating each file yourself, but it is useful for comparing your work with matching lesson files and recovering from mistakes.

Source code means human-readable program files that can be opened, studied, modified, and executed. To use the provided files:

1. Download the course code package.
2. Extract it into a working folder.
3. Open the extracted folder or the relevant Python files in IDLE or PyCharm.
4. Use the matching lesson files as a reference while completing the exercises.

If the files do not open as expected, make sure the download was extracted first and that you opened the extracted project directory or intended Python source file.

Supported and Unsupported Python Versions

Common Setup Problems

The command reports Python 2 or another unsupported version

The terminal command, PATH selection, or IDE project probably points to an older interpreter. Install Python 3 if necessary, then change the command or IDE interpreter configuration to Python 3. Run the version check again before starting the lesson files.

The crawler cannot retrieve a website

There may be no internet connection, the address may be incorrect, DNS may be unavailable, or the destination may not be reachable. Test the address in a browser, confirm network connectivity, check the URL, and try again after access is restored.

PyCharm cannot run the project file

No valid Python interpreter may be assigned to the project. Open the project interpreter settings and select or add the local Python 3 installation.

The downloaded code package does not open correctly

The package may not have been extracted, or the wrong folder or file may be open. Extract the package first, then open the extracted project directory or intended Python source file.

Next Steps

After completing this checklist, review what a web crawler is and continue to create a new project. You can then follow the guide to create a web crawler in Python, parse HTML, and manage crawler URLs.