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.

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):
-    """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)
+def copymode(src, dst, symlinks=False):
+    """Copy mode bits from src to dst.
 
-def copystat(src, dst):
-    """Copy all stat info (mode bits, atime, mtime, flags) from src to dst"""
-    st = os.stat(src)
+    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.
+
+    """
+    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: