Add more typing to safer

safer/__init__.py

@@ -147,32 +147,27 @@
 import contextlib
 import functools
 import io
-import json
 import os
 import shutil
 import sys
 import tempfile
 import traceback
+import typing as t
 from pathlib import Path
-from typing import IO, Callable, Optional, Union
-
-# There's an edge case in #23 I can't yet fix, so I fail
-# deliberately
-BUG_MESSAGE = 'Sorry, safer.writer fails if temp_file (#23)'
 
 __all__ = 'writer', 'open', 'closer', 'dump', 'printer'
 
 
 def writer(
-    stream: Union[Callable, None, IO, Path, str] = None,
-    is_binary: Optional[bool] = None,
+    stream: t.Union[t.Callable, None, t.IO, Path, str] = None,
+    is_binary: t.Optional[bool] = None,
     close_on_exit: bool = False,
     temp_file: bool = False,
     chunk_size: int = 0x100000,
     delete_failures: bool = True,
-    dry_run: Union[bool, Callable] = False,
+    dry_run: t.Union[bool, t.Callable] = False,
     enabled: bool = True,
-) -> Union[Callable, IO]:
+) -> t.Union[t.Callable, t.IO]:
     """
     Write safely to file streams, sockets and callables.
 
@@ -233,7 +228,7 @@ def writer(
     if not enabled:
         return stream
 
-    write: Optional[Callable]
+    write: t.Optional[t.Callable]
 
     if callable(dry_run):
         write, dry_run = dry_run, True
@@ -307,21 +302,26 @@ def write(v):
     return closer.fp
 
 
+# There's an edge case in #23 I can't yet fix, so I fail
+# deliberately
+BUG_MESSAGE = 'Sorry, safer.writer fails if temp_file (#23)'
+
+
 def open(
-    name: Union[Path, str],
+    name: t.Union[Path, str],
     mode: str = 'r',
     buffering: int = -1,
-    encoding: Optional[str] = None,
-    errors: Optional[str] = None,
-    newline: Optional[str] = None,
+    encoding: t.Optional[str] = None,
+    errors: t.Optional[str] = None,
+    newline: t.Optional[str] = None,
     closefd: bool = True,
-    opener: Optional[Callable] = None,
+    opener: t.Optional[t.Callable] = None,
     make_parents: bool = False,
     delete_failures: bool = True,
     temp_file: bool = False,
-    dry_run: Union[bool, Callable] = False,
+    dry_run: t.Union[bool, t.Callable] = False,
     enabled: bool = True,
-) -> IO:
+) -> t.IO:
     """
     Args:
       make_parents: If true, create the parent directory of the file if needed
@@ -443,7 +443,9 @@ def simple_write(value):
     return closer._make_stream(buffering, mode, **kwargs)
 
 
-def closer(stream, is_binary=None, close_on_exit=True, **kwds):
+def closer(
+    stream: t.IO, is_binary: t.Optional[bool] = None, close_on_exit: bool = True, **kwds
+) -> t.Union[t.Callable, t.IO]:
     """
     Like `safer.writer()` but with `close_on_exit=True` by default
 
@@ -453,7 +455,12 @@ def closer(stream, is_binary=None, close_on_exit=True, **kwds):
     return writer(stream, is_binary, close_on_exit, **kwds)
 
 
-def dump(obj, stream=None, dump=None, **kwargs):
+def dump(
+    obj,
+    stream: t.Union[t.Callable, None, t.IO, Path, str] = None,
+    dump: t.Any = None,
+    **kwargs,
+) -> t.Any:
     """
     Safely serialize `obj` as a formatted stream to `fp`` (a
     `.write()`-supporting file-like object, or a filename),
@@ -476,23 +483,34 @@ def dump(obj, stream=None, dump=None, **kwargs):
       kwargs:
         Additional arguments to `dump`.
     """
-    if isinstance(stream, str):
-        name = stream
-        is_binary = False
-    else:
-        name = getattr(stream, 'name', None)
-        mode = getattr(stream, 'mode', None)
+    if not isinstance(stream, str):
+        name = getattr(stream, 'name', '')
+        mode = getattr(stream, 'mode', '')
         if name and mode:
             is_binary = 'b' in mode
         else:
             is_binary = hasattr(stream, 'recv') and hasattr(stream, 'send')
+    else:
+        name = stream
+        is_binary = False
 
-    if name and not dump:
-        dump = Path(name).suffix[1:] or None
-        if dump == 'yml':
-            dump = 'yaml'
+    dump = _get_dumper(dump or Path(name).suffix[1:])
+
+    with t.cast(t.IO, writer(stream)) as fp:
+        if is_binary:
+            write = fp.write
+            fp.write = lambda s: write(s.encode('utf-8'))  # type: ignore
 
+        return dump(obj, fp)
+
+
+def _get_dumper(dump: t.Any) -> t.Callable:
     if isinstance(dump, str):
+        if not dump:
+            dump = 'json'
+        elif dump == 'yml':
+            dump = 'yaml'
+
         try:
             dump = __import__(dump)
         except ImportError:
@@ -501,24 +519,19 @@ def dump(obj, stream=None, dump=None, **kwargs):
             mod, name = dump.rsplit('.', maxsplit=1)
             dump = getattr(__import__(mod), name)
 
-    if dump is None:
-        dump = json.dump
-
-    elif not callable(dump):
-        try:
-            dump = dump.safe_dump
-        except AttributeError:
-            dump = dump.dump
+    if callable(dump):
+        return dump
 
-    with writer(stream) as fp:
-        if is_binary:
-            write = fp.write
-            fp.write = lambda s: write(s.encode('utf-8'))
-        return dump(obj, fp)
+    try:
+        return dump.safe_dump
+    except AttributeError:
+        return dump.dump
 
 
 @contextlib.contextmanager
-def printer(name, mode='w', *args, **kwargs):
+def printer(
+    name: t.Union[Path, str], mode: str = 'w', *args, **kwargs
+) -> t.Generator[t.Callable, None, None]:
     """
     A context manager that yields a function that prints to the opened file,
     only writing to the original file at the exit of the context,