Issue #12715: Add an optional symlinks argument to shutil functions (copyfile,...

Issue #12715: Add an optional symlinks argument to shutil functions (copyfile, copymode, copystat, copy, copy2).
When that parameter is true, symlinks aren't dereferenced and the operation
instead acts on the symlink itself (or creates one, if relevant).

Patch by Hynek Schlawack.

Doc/library/shutil.rst

@@ -45,7 +45,7 @@ Directory and files operations
    be copied.
 
 
-.. function:: copyfile(src, dst)
+.. function:: copyfile(src, dst[, symlinks=False])
 
    Copy the contents (no metadata) of the file named *src* to a file named *dst*.
    *dst* must be the complete target file name; look at :func:`copy` for a copy that
@@ -56,37 +56,56 @@ Directory and files operations
    such as character or block devices and pipes cannot be copied with this
    function.  *src* and *dst* are path names given as strings.
 
+   If *symlinks* is true and *src* is a symbolic link, a new symbolic link will
+   be created instead of copying the file *src* points to.
+
    .. versionchanged:: 3.3
       :exc:`IOError` used to be raised instead of :exc:`OSError`.
+      Added *symlinks* argument.
 
 
-.. function:: copymode(src, dst)
+.. function:: copymode(src, dst[, symlinks=False])
 
    Copy the permission bits from *src* to *dst*.  The file contents, owner, and
-   group are unaffected.  *src* and *dst* are path names given as strings.
+   group are unaffected.  *src* and *dst* are path names given as strings.  If
+   *symlinks* is true, *src* a symbolic link and the operating system supports
+   modes for symbolic links (for example BSD-based ones), the mode of the link
+   will be copied.
 
+   .. versionchanged:: 3.3
+      Added *symlinks* argument.
 
-.. function:: copystat(src, dst)
+.. function:: copystat(src, dst[, symlinks=False])
 
    Copy the permission bits, last access time, last modification time, and flags
    from *src* to *dst*.  The file contents, owner, and group are unaffected.  *src*
-   and *dst* are path names given as strings.
+   and *dst* are path names given as strings.  If *src* and *dst* are both
+   symbolic links and *symlinks* true, the stats of the link will be copied as
+   far as the platform allows.
 
+   .. versionchanged:: 3.3
+      Added *symlinks* argument.
 
-.. function:: copy(src, dst)
+.. function:: copy(src, dst[, symlinks=False]))
 
    Copy the file *src* to the file or directory *dst*.  If *dst* is a directory, a
    file with the same basename as *src*  is created (or overwritten) in the
    directory specified.  Permission bits are copied.  *src* and *dst* are path
-   names given as strings.
+   names given as strings.  If *symlinks* is true, symbolic links won't be
+   followed but recreated instead -- this resembles GNU's :program:`cp -P`.
 
+   .. versionchanged:: 3.3
+      Added *symlinks* argument.
 
-.. function:: copy2(src, dst)
+.. function:: copy2(src, dst[, symlinks=False])
 
    Similar to :func:`copy`, but metadata is copied as well -- in fact, this is just
    :func:`copy` followed by :func:`copystat`.  This is similar to the
-   Unix command :program:`cp -p`.
+   Unix command :program:`cp -p`.  If *symlinks* is true, symbolic links won't
+   be followed but recreated instead -- this resembles GNU's :program:`cp -P`.
 
+   .. versionchanged:: 3.3
+      Added *symlinks* argument.
 
 .. function:: ignore_patterns(\*patterns)
 
@@ -104,9 +123,9 @@ Directory and files operations
    :func:`copy2`.
 
    If *symlinks* is true, symbolic links in the source tree are represented as
-   symbolic links in the new tree, but the metadata of the original links is NOT
-   copied; if false or omitted, the contents and metadata of the linked files
-   are copied to the new tree.
+   symbolic links in the new tree and the metadata of the original links will
+   be copied as far as the platform allows; if false or omitted, the contents
+   and metadata of the linked files are copied to the new tree.
 
    When *symlinks* is false, if the file pointed by the symlink doesn't
    exist, a exception will be added in the list of errors raised in
@@ -140,6 +159,9 @@ Directory and files operations
       Added the *ignore_dangling_symlinks* argument to silent dangling symlinks
       errors when *symlinks* is false.
 
+   .. versionchanged:: 3.3
+      Copy metadata when *symlinks* is false.
+
 
 .. function:: rmtree(path, ignore_errors=False, onerror=None)
 

Lib/shutil.py

@@ -82,8 +82,13 @@ def _samefile(src, dst):
     return (os.path.normcase(os.path.abspath(src)) ==
             os.path.normcase(os.path.abspath(dst)))
 
-def copyfile(src, dst):
-    """Copy data from src to dst"""
+def copyfile(src, dst, symlinks=False):
+    """Copy data from src to dst.
+
+    If optional flag `symlinks` is set and `src` is a symbolic link, a new
+    symlink will be created instead of copying the file it points to.
+
+    """
     if _samefile(src, dst):
         raise Error("`%s` and `%s` are the same file" % (src, dst))
 
@@ -98,54 +103,94 @@ def copyfile(src, dst):
             if stat.S_ISFIFO(st.st_mode):
                 raise SpecialFileError("`%s` is a named pipe" % fn)
 
-    with open(src, 'rb') as fsrc:
-        with open(dst, 'wb') as fdst:
-            copyfileobj(fsrc, fdst)
+    if symlinks and os.path.islink(src):
+        os.symlink(os.readlink(src), dst)
+    else:
+        with open(src, 'rb') as fsrc:
+            with open(dst, 'wb') as fdst:
+                copyfileobj(fsrc, fdst)
+
+def copymode(src, dst, symlinks=False):
+    """Copy mode bits from src to dst.
 
-def copymode(src, dst):
-    """Copy mode bits from src to dst"""
-    if hasattr(os, 'chmod'):
-        st = os.stat(src)
-        mode = stat.S_IMODE(st.st_mode)
-        os.chmod(dst, mode)
+    If the optional flag `symlinks` is set, symlinks aren't followed if and
+    only if both `src` and `dst` are symlinks. If `lchmod` isn't available (eg.
+    Linux), in these cases, this method does nothing.
 
-def copystat(src, dst):
-    """Copy all stat info (mode bits, atime, mtime, flags) from src to dst"""
-    st = os.stat(src)
+    """
+    if symlinks and os.path.islink(src) and os.path.islink(dst):
+        if hasattr(os, 'lchmod'):
+            stat_func, chmod_func = os.lstat, os.lchmod
+        else:
+            return
+    elif hasattr(os, 'chmod'):
+        stat_func, chmod_func = os.stat, os.chmod
+    else:
+        return
+
+    st = stat_func(src)
+    chmod_func(dst, stat.S_IMODE(st.st_mode))
+
+def copystat(src, dst, symlinks=False):
+    """Copy all stat info (mode bits, atime, mtime, flags) from src to dst.
+
+    If the optional flag `symlinks` is set, symlinks aren't followed if and
+    only if both `src` and `dst` are symlinks.
+
+    """
+    def _nop(*args):
+        pass
+
+    if symlinks and os.path.islink(src) and os.path.islink(dst):
+        stat_func = os.lstat
+        utime_func = os.lutimes if hasattr(os, 'lutimes') else _nop
+        chmod_func = os.lchmod if hasattr(os, 'lchmod') else _nop
+        chflags_func = os.lchflags if hasattr(os, 'lchflags') else _nop
+    else:
+        stat_func = os.stat
+        utime_func = os.utime if hasattr(os, 'utime') else _nop
+        chmod_func = os.chmod if hasattr(os, 'chmod') else _nop
+        chflags_func = os.chflags if hasattr(os, 'chflags') else _nop
+
+    st = stat_func(src)
     mode = stat.S_IMODE(st.st_mode)
-    if hasattr(os, 'utime'):
-        os.utime(dst, (st.st_atime, st.st_mtime))
-    if hasattr(os, 'chmod'):
-        os.chmod(dst, mode)
-    if hasattr(os, 'chflags') and hasattr(st, 'st_flags'):
+    utime_func(dst, (st.st_atime, st.st_mtime))
+    chmod_func(dst, mode)
+    if hasattr(st, 'st_flags'):
         try:
-            os.chflags(dst, st.st_flags)
+            chflags_func(dst, st.st_flags)
         except OSError as why:
             if (not hasattr(errno, 'EOPNOTSUPP') or
                 why.errno != errno.EOPNOTSUPP):
                 raise
 
-def copy(src, dst):
+def copy(src, dst, symlinks=False):
     """Copy data and mode bits ("cp src dst").
 
     The destination may be a directory.
 
+    If the optional flag `symlinks` is set, symlinks won't be followed. This
+    resembles GNU's "cp -P src dst".
+
     """
     if os.path.isdir(dst):
         dst = os.path.join(dst, os.path.basename(src))
-    copyfile(src, dst)
-    copymode(src, dst)
+    copyfile(src, dst, symlinks=symlinks)
+    copymode(src, dst, symlinks=symlinks)
 
-def copy2(src, dst):
+def copy2(src, dst, symlinks=False):
     """Copy data and all stat info ("cp -p src dst").
 
     The destination may be a directory.
 
+    If the optional flag `symlinks` is set, symlinks won't be followed. This
+    resembles GNU's "cp -P src dst".
+
     """
     if os.path.isdir(dst):
         dst = os.path.join(dst, os.path.basename(src))
-    copyfile(src, dst)
-    copystat(src, dst)
+    copyfile(src, dst, symlinks=symlinks)
+    copystat(src, dst, symlinks=symlinks)
 
 def ignore_patterns(*patterns):
     """Function that can be used as copytree() ignore parameter.
@@ -212,7 +257,11 @@ def copytree(src, dst, symlinks=False, ignore=None, copy_function=copy2,
             if os.path.islink(srcname):
                 linkto = os.readlink(srcname)
                 if symlinks:
+                    # We can't just leave it to `copy_function` because legacy
+                    # code with a custom `copy_function` may rely on copytree
+                    # doing the right thing.
                     os.symlink(linkto, dstname)
+                    copystat(srcname, dstname, symlinks=symlinks)
                 else:
                     # ignore dangling symlink if the flag is on
                     if not os.path.exists(linkto) and ignore_dangling_symlinks:

Misc/NEWS

@@ -422,6 +422,11 @@ Core and Builtins
 Library
 -------
 
+- Issue #12715: Add an optional symlinks argument to shutil functions
+  (copyfile, copymode, copystat, copy, copy2).  When that parameter is
+  true, symlinks aren't dereferenced and the operation instead acts on the
+  symlink itself (or creates one, if relevant).  Patch by Hynek Schlawack.
+
 - Add a flags parameter to select.epoll.
 
 - Issue #12798: Updated the mimetypes documentation.