Extract file extensions

Return the extension of a filename, handling edge cases like hidden files and directories.

strings parsing file-paths

Write a function `get_extension(filename)` that takes a string `filename` and returns the file extension as a string.

The extension is defined as the substring after the LAST dot (`.`) that appears after the last path separator (if any). If there is no dot after the last separator, return an empty string `''`.

Detailed rules:
- If the filename contains a path (e.g., `'folder/file.txt'`), only consider the part after the last `/`.
- If the filename ends with a dot (e.g., `'file.'`), the extension is an empty string `''`.
- If the filename starts with a dot (e.g., `'.bashrc'`), the dot is considered part of the name, not an extension separator, so return `''`.
- If the filename is exactly `'.'` or `'..'`, return `''`.
- If the filename is empty, return `''`.

Your function should not rely on any external modules.

Constraints

- 0 <= len(filename) <= 1000
- The string contains only printable ASCII characters (no newline).
- Path separators appear as `/` (forward slash).

Example

>>> get_extension('report.pdf')
'pdf'
>>> get_extension('archive.tar.gz')
'gz'
>>> get_extension('folder/file.txt')
'txt'
>>> get_extension('.bashrc')
''

8 points ~10 min

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Hints

First split the filename on `/` and take the last component.

Use `rfind('.')` to find the last dot in that component.

If the dot is at position 0 or absent, return an empty string.

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