fix: append mode on non-existent files (#604)

* fix: append mode on non-existent files

* fix: lint and format

* fix: copy zipfile

* fix: tests

* fix: remove one redundant isinstance check

* fix: refactor

py7zr/py7zr.py

@@ -347,34 +347,35 @@ def __init__(
  self._block_size = blocksize
  else:
  self._block_size = get_default_blocksize()
+
+ # https://github.com/python/cpython/blob/b5e142ba7c2063efe9bb8065c3b0bad33e2a9afa/Lib/zipfile/__init__.py#L1350
  # Check if we were passed a file-like object or not
+ if isinstance(file, os.PathLike):
+ file = os.fspath(file)
  if isinstance(file, str):
- self._filePassed: bool = False
- self.filename: str = file
- if mode == "r":
- self.fp = open(file, "rb")
- elif mode == "w":
- self.fp = open(file, "w+b")
- elif mode == "x":
- self.fp = open(file, "x+b")
- elif mode == "a":
- self.fp = open(file, "r+b")
- else:
- raise ValueError("File open error.")
- self.mode = mode
- elif isinstance(file, pathlib.Path):
+ # No, it's a filename
  self._filePassed = False
- self.filename = str(file)
- if mode == "r":
- self.fp = file.open(mode="rb") # noqa # typeshed issue: 2911
- elif mode == "w":
- self.fp = file.open(mode="w+b") # noqa
- elif mode == "x":
- self.fp = file.open(mode="x+b") # noqa
- elif mode == "a":
- self.fp = file.open(mode="r+b") # noqa
- else:
- raise ValueError("File open error.")
+ self.filename = file
+ modeDict = {
+ "r": "rb",
+ "w": "w+b",
+ "x": "x+b",
+ "a": "r+b",
+ "r+b": "w+b",
+ "w+b": "wb",
+ "x+b": "xb",
+ }
+ filemode = modeDict[mode]
+
+ while True:
+ try:
+ self.fp = open(file, filemode) # type: ignore
+ except OSError:
+ if filemode in modeDict:
+ filemode = modeDict[filemode]
+ continue
+ raise
+ break
  self.mode = mode
  elif isinstance(file, multivolumefile.MultiVolume):
  self._filePassed = True
@@ -401,8 +402,13 @@ def __init__(
  elif mode == "x":
  self._prepare_write(filters, password)
  elif mode == "a":
- self._real_get_contents(password)
- self._prepare_append(filters, password)
+ try:
+ # Append if it's an existing 7zip file
+ self._real_get_contents(password)
+ self._prepare_append(filters, password)
+ except Bad7zFile:
+ # Not an existing 7zip file, write instead
+ self._prepare_write(filters, password)
  else:
  raise ValueError("Mode must be 'r', 'w', 'x', or 'a'") # never come here
  except Exception as e:
@@ -776,9 +782,13 @@ def set_encrypted_header(self, mode: bool) -> None:
 
  @staticmethod
  def _check_7zfile(fp: Union[BinaryIO, io.BufferedReader, io.IOBase]) -> bool:
- result = MAGIC_7Z == fp.read(len(MAGIC_7Z))[: len(MAGIC_7Z)]
- fp.seek(-len(MAGIC_7Z), 1)
- return result
+ try:
+ result = MAGIC_7Z == fp.read(len(MAGIC_7Z))[: len(MAGIC_7Z)]
+ fp.seek(-len(MAGIC_7Z), 1)
+ return result
+ except OSError:
+ # A new empty file raises OSError
+ return False
 
  def _get_method_names(self) -> List[str]:
  try:

tests/test_basic.py

@@ -41,6 +41,13 @@ def test_basic_append_mode(tmp_path):
  archive.write(os.path.join(testdata_path, "test1.txt"), "test1.txt")
 
 
+@pytest.mark.api
+def test_basic_append_mode_on_non_existent_file(tmp_path):
+ target = tmp_path.joinpath("test_non_existent_file.7z")
+ with py7zr.SevenZipFile(target, mode="a") as archive:
+ archive.write(os.path.join(testdata_path, "test1.txt"), "test1.txt")
+
+
 @pytest.mark.api
 def test_basic_wrong_option_value(tmp_path):
  with pytest.raises(ValueError):