diff --git a/fire/__main__.py b/fire/__main__.py
index 11fb1b42..140b4a76 100644
--- a/fire/__main__.py
+++ b/fire/__main__.py
@@ -54,14 +54,14 @@ def import_from_file_path(path):
   """
 
   if not os.path.exists(path):
-    raise IOError('Given file path does not exist.')
+    raise OSError('Given file path does not exist.')
 
   module_name = os.path.basename(path)
 
   spec = util.spec_from_file_location(module_name, path)
 
   if spec is None:
-    raise IOError('Unable to load module from specified path.')
+    raise OSError('Unable to load module from specified path.')
 
   module = util.module_from_spec(spec)  # pylint: disable=no-member
   spec.loader.exec_module(module)  # pytype: disable=attribute-error
@@ -104,7 +104,7 @@ def import_module(module_or_filename):
     return import_from_file_path(module_or_filename)
 
   if os.path.sep in module_or_filename:  # Use / to detect if it was a filename.
-    raise IOError('Fire was passed a filename which could not be found.')
+    raise OSError('Fire was passed a filename which could not be found.')
 
   return import_from_module_name(module_or_filename)  # Assume it's a module.
 
diff --git a/fire/core.py b/fire/core.py
index 6cd1907e..26a25753 100644
--- a/fire/core.py
+++ b/fire/core.py
@@ -199,7 +199,7 @@ def __init__(self, code, component_trace):
       code: (int) Exit code for the Fire CLI.
       component_trace: (FireTrace) The trace for the Fire command.
     """
-    super(FireExit, self).__init__(code)
+    super().__init__(code)
     self.trace = component_trace
 
 
diff --git a/fire/decorators_test.py b/fire/decorators_test.py
index a316b79f..9988743c 100644
--- a/fire/decorators_test.py
+++ b/fire/decorators_test.py
@@ -19,7 +19,7 @@
 from fire import testutils
 
 
-class NoDefaults(object):
+class NoDefaults:
   """A class for testing decorated functions without default values."""
 
   @decorators.SetParseFns(count=int)
@@ -40,7 +40,7 @@ def double(count):
   return 2 * count
 
 
-class WithDefaults(object):
+class WithDefaults:
 
   @decorators.SetParseFns(float)
   def example1(self, arg1=10):
@@ -51,14 +51,14 @@ def example2(self, arg1=10):
     return arg1, type(arg1)
 
 
-class MixedArguments(object):
+class MixedArguments:
 
   @decorators.SetParseFns(float, arg2=str)
   def example3(self, arg1, arg2):
     return arg1, arg2
 
 
-class PartialParseFn(object):
+class PartialParseFn:
 
   @decorators.SetParseFns(arg1=str)
   def example4(self, arg1, arg2):
@@ -69,7 +69,7 @@ def example5(self, arg1, arg2):
     return arg1, arg2
 
 
-class WithKwargs(object):
+class WithKwargs:
 
   @decorators.SetParseFns(mode=str, count=int)
   def example6(self, **kwargs):
@@ -79,7 +79,7 @@ def example6(self, **kwargs):
     )
 
 
-class WithVarArgs(object):
+class WithVarArgs:
 
   @decorators.SetParseFn(str)
   def example7(self, arg1, arg2=None, *varargs, **kwargs):  # pylint: disable=keyword-arg-before-vararg
diff --git a/fire/helptext.py b/fire/helptext.py
index e57eb7d8..9b578fac 100644
--- a/fire/helptext.py
+++ b/fire/helptext.py
@@ -767,7 +767,7 @@ def _CreateAvailabilityLine(header, items,
   return indented_header + indented_items_text[len(indented_header):] + '\n'
 
 
-class ActionGroup(object):
+class ActionGroup:
   """A group of actions of the same kind."""
 
   def __init__(self, name, plural):
diff --git a/fire/helptext_test.py b/fire/helptext_test.py
index 4d35dc0a..d1a3f368 100644
--- a/fire/helptext_test.py
+++ b/fire/helptext_test.py
@@ -27,7 +27,7 @@
 class HelpTest(testutils.BaseTestCase):
 
   def setUp(self):
-    super(HelpTest, self).setUp()
+    super().setUp()
     os.environ['ANSI_COLORS_DISABLED'] = '1'
 
   def testHelpTextNoDefaults(self):
diff --git a/fire/inspectutils.py b/fire/inspectutils.py
index a3ae7c27..d1438972 100644
--- a/fire/inspectutils.py
+++ b/fire/inspectutils.py
@@ -22,7 +22,7 @@
 from fire import docstrings
 
 
-class FullArgSpec(object):
+class FullArgSpec:
   """The arguments of a function, as in Python 3's inspect.FullArgSpec."""
 
   def __init__(self, args=None, varargs=None, varkw=None, defaults=None,
@@ -229,7 +229,7 @@ def GetFileAndLine(component):
   try:
     unused_code, lineindex = inspect.findsource(component)
     lineno = lineindex + 1
-  except (IOError, IndexError):
+  except (OSError, IndexError):
     lineno = None
 
   return filename, lineno
@@ -268,7 +268,7 @@ def Info(component):
   try:
     unused_code, lineindex = inspect.findsource(component)
     info['line'] = lineindex + 1
-  except (TypeError, IOError):
+  except (TypeError, OSError):
     info['line'] = None
 
   if 'docstring' in info:
diff --git a/fire/main_test.py b/fire/main_test.py
index a0184620..a2723347 100644
--- a/fire/main_test.py
+++ b/fire/main_test.py
@@ -43,7 +43,7 @@ class MainModuleFileTest(testutils.BaseTestCase):
   """Tests to verify correct import behavior for file executables."""
 
   def setUp(self):
-    super(MainModuleFileTest, self).setUp()
+    super().setUp()
     self.file = tempfile.NamedTemporaryFile(suffix='.py')  # pylint: disable=consider-using-with
     self.file.write(b'class Foo:\n  def double(self, n):\n    return 2 * n\n')
     self.file.flush()
diff --git a/fire/parser_fuzz_test.py b/fire/parser_fuzz_test.py
index 9739ec4e..10f497cf 100644
--- a/fire/parser_fuzz_test.py
+++ b/fire/parser_fuzz_test.py
@@ -53,7 +53,7 @@ def testDefaultParseValueFuzz(self, value):
       result = parser.DefaultParseValue(value)
     except TypeError:
       # It's OK to get a TypeError if the string has the null character.
-      if u'\x00' in value:
+      if '\x00' in value:
         return
       raise
     except MemoryError:
diff --git a/fire/test_components.py b/fire/test_components.py
index eb3a9e24..2dc4e0cc 100644
--- a/fire/test_components.py
+++ b/fire/test_components.py
@@ -43,7 +43,7 @@ def function_with_help(help=True):  # pylint: disable=redefined-builtin
   return help
 
 
-class Empty(object):
+class Empty:
   pass
 
 
@@ -51,20 +51,20 @@ class OldStyleEmpty:  # pylint: disable=old-style-class,no-init
   pass
 
 
-class WithInit(object):
+class WithInit:
 
   def __init__(self):
     pass
 
 
-class ErrorInConstructor(object):
+class ErrorInConstructor:
 
   def __init__(self, value='value'):
     self.value = value
     raise ValueError('Error in constructor')
 
 
-class WithHelpArg(object):
+class WithHelpArg:
   """Test class for testing when class has a help= arg."""
 
   def __init__(self, help=True):  # pylint: disable=redefined-builtin
@@ -72,7 +72,7 @@ def __init__(self, help=True):  # pylint: disable=redefined-builtin
     self.dictionary = {'__help': 'help in a dict'}
 
 
-class NoDefaults(object):
+class NoDefaults:
 
   def double(self, count):
     return 2 * count
@@ -81,7 +81,7 @@ def triple(self, count):
     return 3 * count
 
 
-class WithDefaults(object):
+class WithDefaults:
   """Class with functions that have default arguments."""
 
   def double(self, count=0):
@@ -115,7 +115,7 @@ def triple(self, count=0):
     return 3 * count
 
 
-class MixedDefaults(object):
+class MixedDefaults:
 
   def ten(self):
     return 10
@@ -127,7 +127,7 @@ def identity(self, alpha, beta='0'):
     return alpha, beta
 
 
-class SimilarArgNames(object):
+class SimilarArgNames:
 
   def identity(self, bool_one=False, bool_two=False):
     return bool_one, bool_two
@@ -136,13 +136,13 @@ def identity2(self, a=None, alpha=None):
     return a, alpha
 
 
-class CapitalizedArgNames(object):
+class CapitalizedArgNames:
 
   def sum(self, Delta=1.0, Gamma=2.0):  # pylint: disable=invalid-name
     return Delta + Gamma
 
 
-class Annotations(object):
+class Annotations:
 
   def double(self, count=0):
     return 2 * count
@@ -154,7 +154,7 @@ def triple(self, count=0):
   triple.__annotations__ = {'count': float}
 
 
-class TypedProperties(object):
+class TypedProperties:
   """Test class for testing Python Fire with properties of various types."""
 
   def __init__(self):
@@ -173,7 +173,7 @@ def __init__(self):
     self.gamma = 'myexcitingstring'
 
 
-class VarArgs(object):
+class VarArgs:
   """Test class for testing Python Fire with a property with varargs."""
 
   def cumsums(self, *items):
@@ -191,7 +191,7 @@ def varchars(self, alpha=0, beta=0, *chars):  # pylint: disable=keyword-arg-befo
     return alpha, beta, ''.join(chars)
 
 
-class Underscores(object):
+class Underscores:
 
   def __init__(self):
     self.underscore_example = 'fish fingers'
@@ -200,20 +200,20 @@ def underscore_function(self, underscore_arg):
     return underscore_arg
 
 
-class BoolConverter(object):
+class BoolConverter:
 
   def as_bool(self, arg=False):
     return bool(arg)
 
 
-class ReturnsObj(object):
+class ReturnsObj:
 
   def get_obj(self, *items):
     del items  # Unused
     return BoolConverter()
 
 
-class NumberDefaults(object):
+class NumberDefaults:
 
   def reciprocal(self, divisor=10.0):
     return 1.0 / divisor
@@ -222,7 +222,7 @@ def integer_reciprocal(self, divisor=10):
     return 1.0 / divisor
 
 
-class InstanceVars(object):
+class InstanceVars:
 
   def __init__(self, arg1, arg2):
     self.arg1 = arg1
@@ -232,7 +232,7 @@ def run(self, arg1, arg2):
     return (self.arg1, self.arg2, arg1, arg2)
 
 
-class Kwargs(object):
+class Kwargs:
 
   def props(self, **kwargs):
     return kwargs
@@ -244,13 +244,13 @@ def run(self, positional, named=None, **kwargs):
     return (positional, named, kwargs)
 
 
-class ErrorRaiser(object):
+class ErrorRaiser:
 
   def fail(self):
     raise ValueError('This error is part of a test.')
 
 
-class NonComparable(object):
+class NonComparable:
 
   def __eq__(self, other):
     raise ValueError('Instances of this class cannot be compared.')
@@ -259,7 +259,7 @@ def __ne__(self, other):
     raise ValueError('Instances of this class cannot be compared.')
 
 
-class EmptyDictOutput(object):
+class EmptyDictOutput:
 
   def totally_empty(self):
     return {}
@@ -268,7 +268,7 @@ def nothing_printable(self):
     return {'__do_not_print_me': 1}
 
 
-class CircularReference(object):
+class CircularReference:
 
   def create(self):
     x = {}
@@ -276,7 +276,7 @@ def create(self):
     return x
 
 
-class OrderedDictionary(object):
+class OrderedDictionary:
 
   def empty(self):
     return collections.OrderedDict()
@@ -288,7 +288,7 @@ def non_empty(self):
     return ordered_dict
 
 
-class NamedTuple(object):
+class NamedTuple:
   """Functions returning named tuples used for testing."""
 
   def point(self):
@@ -304,7 +304,7 @@ def matching_names(self):
     return Point(x='x', y='y')
 
 
-class CallableWithPositionalArgs(object):
+class CallableWithPositionalArgs:
   """Test class for supporting callable."""
 
   TEST = 1
@@ -326,12 +326,12 @@ def coordinate_sum(self):
     return self.x + self.y
 
 
-class CallableWithKeywordArgument(object):
+class CallableWithKeywordArgument:
   """Test class for supporting callable."""
 
   def __call__(self, **kwargs):
     for key, value in kwargs.items():
-      print('%s: %s' % (key, value))
+      print('{}: {}'.format(key, value))
 
   def print_msg(self, msg):
     print(msg)
@@ -340,7 +340,7 @@ def print_msg(self, msg):
 CALLABLE_WITH_KEYWORD_ARGUMENT = CallableWithKeywordArgument()
 
 
-class ClassWithDocstring(object):
+class ClassWithDocstring:
   """Test class for testing help text output.
 
   This is some detail description of this test class.
@@ -363,7 +363,7 @@ def print_msg(self, msg=None):
     print(msg)
 
 
-class ClassWithMultilineDocstring(object):
+class ClassWithMultilineDocstring:
   """Test class for testing help text output with multiline docstring.
 
   This is a test class that has a long docstring description that spans across
@@ -413,7 +413,7 @@ class Color(enum.Enum):
   BLUE = 3
 
 
-class HasStaticAndClassMethods(object):
+class HasStaticAndClassMethods:
   """A class with a static method and a class method."""
 
   CLASS_STATE = 1
@@ -467,7 +467,7 @@ def fn_with_code_in_docstring():
   return True
 
 
-class BinaryCanvas(object):
+class BinaryCanvas:
   """A canvas with which to make binary art, one bit at a time."""
 
   def __init__(self, size=10):
@@ -500,7 +500,7 @@ def set(self, value):
     return self
 
 
-class DefaultMethod(object):
+class DefaultMethod:
 
   def double(self, number):
     return 2 * number
@@ -511,7 +511,7 @@ def _missing():
     return _missing
 
 
-class InvalidProperty(object):
+class InvalidProperty:
 
   def double(self, number):
     return 2 * number
diff --git a/fire/test_components_py3.py b/fire/test_components_py3.py
index 17fb932c..192302d3 100644
--- a/fire/test_components_py3.py
+++ b/fire/test_components_py3.py
@@ -31,7 +31,7 @@ def identity(self, *, alpha, beta='0'):
     return alpha, beta
 
 
-class KeywordOnly(object):
+class KeywordOnly:
 
   def double(self, *, count):
     return count * 2
@@ -43,7 +43,7 @@ def with_default(self, *, x="x"):
     print("x: " + x)
 
 
-class LruCacheDecoratedMethod(object):
+class LruCacheDecoratedMethod:
 
   @functools.lru_cache()
   def lru_cache_in_class(self, arg1):
@@ -55,13 +55,13 @@ def lru_cache_decorated(arg1):
   return arg1
 
 
-class WithAsyncio(object):
+class WithAsyncio:
 
   async def double(self, count=0):
     return 2 * count
 
 
-class WithTypes(object):
+class WithTypes:
   """Class with functions that have default arguments and types."""
 
   def double(self, count: float) -> float:
@@ -83,7 +83,7 @@ def long_type(
     return long_obj
 
 
-class WithDefaultsAndTypes(object):
+class WithDefaultsAndTypes:
   """Class with functions that have default arguments and types."""
 
   def double(self, count: float = 0) -> float:
diff --git a/fire/trace.py b/fire/trace.py
index 68b48ce5..3a75cc9c 100644
--- a/fire/trace.py
+++ b/fire/trace.py
@@ -38,7 +38,7 @@
 INTERACTIVE_MODE = 'Entered interactive mode'
 
 
-class FireTrace(object):
+class FireTrace:
   """A FireTrace represents the steps taken during a single Fire execution.
 
   A FireTrace consists of a sequence of FireTraceElement objects. Each element
@@ -238,7 +238,7 @@ def NeedsSeparatingHyphenHyphen(self, flag='help'):
             or flag in spec.kwonlyargs)
 
 
-class FireTraceElement(object):
+class FireTraceElement:
   """A FireTraceElement represents a single step taken by a Fire execution.
 
   Examples of a FireTraceElement are the instantiation of a class or the