Fixed a couple of pyright errors as long as I was playing around with it.

bs4/__init__.py

@@ -51,6 +51,7 @@ __all__ = [
 ]
 
 from collections import Counter
+import io
 import sys
 import warnings
 
@@ -349,7 +350,7 @@ class BeautifulSoup(Tag):
         original_builder = builder
         original_features = features
 
-        builder_class: Type[TreeBuilder]
+        builder_class: Optional[Type[TreeBuilder]] = None
         if isinstance(builder, type):
             # A builder class was passed in; it needs to be instantiated.
             builder_class = builder
@@ -372,6 +373,7 @@ class BeautifulSoup(Tag):
         # builder, or we have a builder_class that we can instantiate
         # with the remaining **kwargs.
         if builder is None:
+            assert builder_class is not None
             builder = builder_class(**kwargs)
             if (
                 not original_builder
@@ -437,7 +439,7 @@ class BeautifulSoup(Tag):
         self.parse_only = parse_only
 
         if hasattr(markup, "read"):  # It's a file-type object.
-            markup = markup.read()
+            markup = cast(io.IOBase, markup).read()
         elif not isinstance(markup, (bytes, str)) and not hasattr(markup, "__len__"):
             raise TypeError(
                 f"Incoming markup is of an invalid type: {markup!r}. Markup must be a string, a bytestring, or an open filehandle."
@@ -1118,6 +1120,7 @@ class BeautifulSoup(Tag):
         # argument to this method (or a keyword argument with the old
         # name), we can handle it and put out a DeprecationWarning.
         warning: Optional[str] = None
+        pretty_print: Optional[bool] = None
         if isinstance(indent_level, bool):
             if indent_level is True:
                 indent_level = 0

bs4/builder/__init__.py

@@ -136,7 +136,7 @@ class TreeBuilderRegistry(object):
                 if candidates is None:
                     candidates = we_have_the_feature
                     candidate_set = set(candidates)
-                else:
+                elif candidate_set is not None:
                     # Eliminate any candidates that don't have this feature.
                     candidate_set = candidate_set.intersection(set(we_have_the_feature))
 
@@ -508,7 +508,7 @@ class HTMLTreeBuilder(TreeBuilder):
 
     #: Some HTML tags are defined as having no contents. Beautiful Soup
     #: treats these specially.
-    DEFAULT_EMPTY_ELEMENT_TAGS: Set[str] = set(
+    DEFAULT_EMPTY_ELEMENT_TAGS: Optional[Set[str]] = set(
         [
             # These are from HTML5.
             "area",

bs4/builder/_html5lib.py

@@ -75,7 +75,7 @@ class HTML5TreeBuilder(HTMLTreeBuilder):
 
     NAME: str = "html5lib"
 
-    features: Sequence[str] = [NAME, PERMISSIVE, HTML_5, HTML]
+    features: Iterable[str] = [NAME, PERMISSIVE, HTML_5, HTML]
 
     #: html5lib can tell us which line number and position in the
     #: original file is the source of an element.

bs4/element.py

@@ -1512,7 +1512,7 @@ class Doctype(PreformattedString):
 
     @classmethod
     def _string_for_name_and_ids(
-        self, name: str, pub_id: Optional[str], system_id: Optional[str]
+        cls, name: str, pub_id: Optional[str], system_id: Optional[str]
     ) -> str:
         """Generate a string to be used as the basis of a Doctype object.