xcp/cpiofile.py: Add type comments to fix static type checking

This adds type comments to fix static type checking by mypy & pyright.

The goal is to be able to use the pyright type checker which is
used by the language backend of the Python extension of vscode.

It can be also used standalone for CI/CD, even in GitHub actions.

Signed-off-by: Bernhard Kaindl <bernhard.kaindl@cloud.com>

Author: bernhardkaindl

.coveragerc

@@ -18,6 +18,7 @@ exclude_lines =
     # Don't complain if non-runnable code isn't run:
     if 0:
     if __name__ == .__main__.:
+    if TYPE_CHECKING:
 
 precision = 1
 include =

xcp/cpiofile.py

@@ -55,10 +55,14 @@
 import struct
 import copy
 import io
-from typing import cast
+from typing import IO, TYPE_CHECKING, Any, cast
 
 import six
 
+if TYPE_CHECKING:
+    from bz2 import _ReadBinaryMode, _WriteBinaryMode
+    from gzip import GzipFile
+
 if sys.platform == 'mac':
     # This module needs work for MacOS9, especially in the area of pathname
     # handling. In many places it is assumed a simple substitution of / by the
@@ -557,6 +561,7 @@ class which (unlike gzip.GzipFile) has no support for
     """
 
     def __init__(self, fileobj, mode):
+        # type:(IO[Any], _ReadBinaryMode | _WriteBinaryMode) -> None
         _CMPProxy.__init__(self, fileobj, mode)
         self.init()
 
@@ -1069,6 +1074,7 @@ def open(cls, name=None, mode="r", fileobj=None, bufsize=20*512):
 
     @classmethod
     def cpioopen(cls, name, mode="r", fileobj=None):
+        # type:(str, _ReadBinaryMode | _WriteBinaryMode, IO[Any] | GzipFile | None) -> CpioFile
         """Open uncompressed cpio archive name for reading or writing.
         """
         if len(mode) > 1 or mode not in "raw":
@@ -1100,6 +1106,7 @@ def gzopen(cls, name, mode="r", fileobj=None, compresslevel=9):
 
     @classmethod
     def bz2open(cls, name, mode="r", fileobj=None, compresslevel=9):
+        # type:(str, _ReadBinaryMode | _WriteBinaryMode, IO[Any] | None, int) -> CpioFile
         """Open bzip2 compressed cpio archive name for reading or writing.
            Appending is not allowed.
         """
@@ -1112,7 +1119,7 @@ def bz2open(cls, name, mode="r", fileobj=None, compresslevel=9):
             raise CompressionError("bz2 module is not available")
 
         if fileobj is not None:
-            fileobj = _BZ2Proxy(fileobj, mode)
+            fileobj = cast(IO[Any], _BZ2Proxy(fileobj, mode))  # pragma: no cover
         else:
             fileobj = bz2.BZ2File(name, mode, compresslevel=compresslevel)