diff --git a/lib/yaml/constructor.py b/lib/yaml/constructor.py
index 859c9494..094b3e01 100644
--- a/lib/yaml/constructor.py
+++ b/lib/yaml/constructor.py
@@ -497,7 +497,7 @@ def find_python_module(self, name, mark, unsafe=False):
             except ImportError, exc:
                 raise ConstructorError("while constructing a Python module", mark,
                         "cannot find module %r (%s)" % (name.encode('utf-8'), exc), mark)
-        if not name in sys.modules:
+        if name not in sys.modules:
             raise ConstructorError("while constructing a Python module", mark,
                     "module %r is not imported" % name.encode('utf-8'), mark)
         return sys.modules[name]
@@ -517,7 +517,7 @@ def find_python_name(self, name, mark, unsafe=False):
             except ImportError, exc:
                 raise ConstructorError("while constructing a Python object", mark,
                         "cannot find module %r (%s)" % (module_name.encode('utf-8'), exc), mark)
-        if not module_name in sys.modules:
+        if module_name not in sys.modules:
             raise ConstructorError("while constructing a Python object", mark,
                     "module %r is not imported" % module_name.encode('utf-8'), mark)
         module = sys.modules[module_name]
diff --git a/lib/yaml/loader.py b/lib/yaml/loader.py
index a79182ea..4d773c3c 100644
--- a/lib/yaml/loader.py
+++ b/lib/yaml/loader.py
@@ -51,7 +51,7 @@ def __init__(self, stream):
 # UnsafeLoader is the same as Loader (which is and was always unsafe on
 # untrusted input). Use of either Loader or UnsafeLoader should be rare, since
 # FullLoad should be able to load almost all YAML safely. Loader is left intact
-# to ensure backwards compatability.
+# to ensure backwards compatibility.
 class UnsafeLoader(Reader, Scanner, Parser, Composer, Constructor, Resolver):
 
     def __init__(self, stream):
diff --git a/lib3/yaml/constructor.py b/lib3/yaml/constructor.py
index fb4f1e9f..f8d71a13 100644
--- a/lib3/yaml/constructor.py
+++ b/lib3/yaml/constructor.py
@@ -513,7 +513,7 @@ def find_python_module(self, name, mark, unsafe=False):
             except ImportError as exc:
                 raise ConstructorError("while constructing a Python module", mark,
                         "cannot find module %r (%s)" % (name, exc), mark)
-        if not name in sys.modules:
+        if name not in sys.modules:
             raise ConstructorError("while constructing a Python module", mark,
                     "module %r is not imported" % name, mark)
         return sys.modules[name]
@@ -533,7 +533,7 @@ def find_python_name(self, name, mark, unsafe=False):
             except ImportError as exc:
                 raise ConstructorError("while constructing a Python object", mark,
                         "cannot find module %r (%s)" % (module_name, exc), mark)
-        if not module_name in sys.modules:
+        if module_name not in sys.modules:
             raise ConstructorError("while constructing a Python object", mark,
                     "module %r is not imported" % module_name, mark)
         module = sys.modules[module_name]
diff --git a/lib3/yaml/loader.py b/lib3/yaml/loader.py
index 414cb2c1..e90c1122 100644
--- a/lib3/yaml/loader.py
+++ b/lib3/yaml/loader.py
@@ -51,7 +51,7 @@ def __init__(self, stream):
 # UnsafeLoader is the same as Loader (which is and was always unsafe on
 # untrusted input). Use of either Loader or UnsafeLoader should be rare, since
 # FullLoad should be able to load almost all YAML safely. Loader is left intact
-# to ensure backwards compatability.
+# to ensure backwards compatibility.
 class UnsafeLoader(Reader, Scanner, Parser, Composer, Constructor, Resolver):
 
     def __init__(self, stream):