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Editorial Team
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Asked: 2026-05-26T06:42:57+00:00

Under Unix, os.path.normpath collapses multiple slashes into single ones except when exactly two slashes

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Under Unix, os.path.normpath collapses multiple slashes into single ones except when exactly two slashes appear that the start of the path. Why the exception?

To illustrate, I get the following transformations:

//double/slash/stays -> //double/slash/stays
/double/slash//gone// -> /double/slash/gone/
double//slash//gone/ -> double/slash/gone
///triple/slash/gone -> /triple/slash/gone
////quad/slash/gone -> /quad/slash/gone

This seems strange to me. I can vaguely imagine this is useful for SMB mounts or URLS, but I don’t think I care about those. Is there any hidden wisdom to Python’s behaviour, or should I just collapse the leading // myself?

[update]
In view of the answer below, it looks like the best thing is not to collapse the //, but to either just accept it, or to treat it as an error.

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1 Answer

  1. Editorial Team

    Because POSIX allows treating a path beginning with two slashes in an implementation-defined manner. In other words, //foo does not necessarily mean the same thing as /foo on all POSIX systems.

    From IEEE Std 1003.1:

    A pathname that begins with two successive slashes may be interpreted
    in an implementation-defined manner, although more than two leading
    slashes shall be treated as a single slash.

    See also this bug report (which was closed as "not a bug").

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