The last strings shouldn't begin with a slash. In the event that they start with a slash, at that point they're viewed as an "absolute path" and everything before them is disposed of.
Citing the Python docs for os.path.join:
If a component is an absolute path, all previous components are thrown away and joining continues from the absolute path component.
Note on Windows, the conduct according to driving letters, which appears to have changed contrasted with before Python forms:
On Windows, the drive letter is not reset when an absolute path component (e.g., r'\foo') is encountered. If a component contains a drive letter, all previous components are thrown away and the drive letter is reset. Note that since there is a current directory for each drive, os.path.join("c:", "foo") represents a path relative to the current directory on drive C: (c:foo), not c:\foo.
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