Extract domain from URL

Parse URLs and pull out the clean domain name.

url parsing strings

Write a function `extract_domain(url)` that takes a URL string and returns the domain name. The domain name is defined as the hostname without the port (if present) and without the leading 'www.' part. The URL may include a scheme (http://, https://), and may include a path, query string, or fragment. All URLs are valid and use only lowercase letters.

Specifically:
- Remove the scheme if present (anything before '://').
- If the remaining string contains a colon followed by a port number, remove the port.
- If the hostname starts with 'www.', remove that prefix.
- Ignore everything after the first '/' (the path), also ignore '?' or '#' if they appear without a slash.
- The function should return the resulting domain string.

Example:
- `extract_domain('https://www.example.com/path')` returns `'example.com'`.
- `extract_domain('http://sub.domain.org:8080?a=1')` returns `'sub.domain.org'`.

Implement the function in Python.

Constraints

Input URL length is between 1 and 200 characters. The input is a valid URL with a scheme and hostname. The hostname is composed of alphanumeric characters and dots. The port (if present) is a positive integer. Output length is between 1 and 200 characters. Time complexity should be O(n), where n is the length of the URL.

Example

>>> extract_domain('https://www.example.com/path')
'example.com'
>>> extract_domain('http://sub.domain.org:8080?a=1')
'sub.domain.org'
>>> extract_domain('https://example.co.uk')
'example.co.uk'

8 points ~12 min

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Hints

First split on '://' to remove the scheme.

Then split on the first '/' or '?' or '#' to isolate the host:port part.

Remove the port by splitting on ':'.

Finally, strip the leading 'www.' if present.

Test Results

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