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\section{Standard Module \sectcode{posixpath}}

This module implements some useful functions on POSIX pathnames.

\renewcommand{\indexsubitem}{(in module posixpath)}
Return the base name of pathname
This is the second half of the pair returned by

Return the longest string that is a prefix of all strings in
is empty, return the empty string (\code{''}).

Return true if
refers to an existing path.

Return the argument with an initial component of \samp{\~} or
\samp{\~\var{user}} replaced by that \var{user}'s home directory.  An
initial \samp{\~{}} is replaced by the environment variable \code{\${}HOME};
an initial \samp{\~\var{user}} is looked up in the password directory through
the built-in module \code{pwd}.  If the expansion fails, or if the
path does not begin with a tilde, the path is returned unchanged.

Return the argument with environment variables expanded.  Substrings
of the form \samp{\$\var{name}} or \samp{\$\{\var{name}\}} are
replaced by the value of environment variable \var{name}.  Malformed
variable names and references to non-existing variables are left

Return true if \var{p} is an absolute pathname (begins with a slash).

Return true if \var{p} is an existing regular file.  This follows
symbolic links, so both islink() and isfile() can be true for the same

Return true if \var{p} is an existing directory.  This follows
symbolic links, so both islink() and isdir() can be true for the same

Return true if
refers to a directory entry that is a symbolic link.
Always false if symbolic links are not supported.

Return true if \var{p} is a mount point.  (This currently checks whether
\code{\var{p}/..} is on a different device from \var{p} or whether
\code{\var{p}/..} and \var{p} point to the same i-node on the same
device --- is this test correct for all \UNIX{} and POSIX variants?)

\begin{funcdesc}{join}{p\, q}
Join the paths
\var{q} intelligently:
is an absolute path, the return value is
Otherwise, the concatenation of
is returned, with a slash (\code{'/'}) inserted unless
is empty or ends in a slash.

Normalize the case of a pathname.  This returns the path unchanged;
however, a similar function in \code{macpath} converts upper case to
lower case.

\begin{funcdesc}{samefile}{p\, q}
Return true if both pathname arguments refer to the same file or directory
(as indicated by device number and i-node number).
Raise an exception if a stat call on either pathname fails.

Split the pathname \var{p} in a pair \code{(\var{head}, \var{tail})}, where
\var{tail} is the last pathname component and \var{head} is
everything leading up to that.  If \var{p} ends in a slash (except if
it is the root), the trailing slash is removed and the operation
applied to the result; otherwise, \code{join(\var{head}, \var{tail})} equals
\var{p}.  The \var{tail} part never contains a slash.  Some boundary
cases: if \var{p} is the root, \var{head} equals \var{p} and
\var{tail} is empty; if \var{p} is empty, both \var{head} and
\var{tail} are empty; if \var{p} contains no slash, \var{head} is
empty and \var{tail} equals \var{p}.

Split the pathname \var{p} in a pair \code{(\var{root}, \var{ext})}
such that \code{\var{root} + \var{ext} == \var{p}},
the last component of \var{root} contains no periods,
and \var{ext} is empty or begins with a period.

\begin{funcdesc}{walk}{p\, visit\, arg}
Calls the function \var{visit} with arguments
\code{(\var{arg}, \var{dirname}, \var{names})} for each directory in the
directory tree rooted at \var{p} (including \var{p} itself, if it is a
directory).  The argument \var{dirname} specifies the visited directory,
the argument \var{names} lists the files in the directory (gotten from
\code{posix.listdir(\var{dirname})}).  The \var{visit} function may
modify \var{names} to influence the set of directories visited below
\var{dirname}, e.g., to avoid visiting certain parts of the tree.  (The
object referred to by \var{names} must be modified in place, using
\code{del} or slice assignment.)