diff --git a/docs/faq.rst b/docs/faq.rst
index f58d2639e7..fe3541f535 100644
--- a/docs/faq.rst
+++ b/docs/faq.rst
@@ -45,7 +45,7 @@ How can I make an App dependent on multiple inputs?
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 You can pass any number of futures in to a single App either as positional arguments
-or as a list of futures via the special keyword ``inputs=()``.
+or as a list of futures via the special keyword ``inputs``.
 The App will wait for all inputs to be satisfied before execution.
 
 
diff --git a/docs/historical/changelog.rst b/docs/historical/changelog.rst
index 931998f93d..770c62bc06 100644
--- a/docs/historical/changelog.rst
+++ b/docs/historical/changelog.rst
@@ -301,7 +301,7 @@ New Functionality
    .. code-block:: python
 
       @bash_app
-      def cat(inputs=(), outputs=()):
+      def cat(inputs, outputs):
            return 'cat {} > {}'.format(inputs[0], outputs[0])
 
       concat = cat(inputs=['hello-0.txt'],
@@ -314,7 +314,7 @@ New Functionality
       from parsl import File
 
       @bash_app
-      def cat(inputs=(), outputs=()):
+      def cat(inputs, outputs):
            return 'cat {} > {}'.format(inputs[0].filepath, outputs[0].filepath)
 
       concat = cat(inputs=[File('hello-0.txt')],
@@ -328,7 +328,7 @@ New Functionality
       from parsl import File
 
       @bash_app
-      def cat(inputs=(), outputs=()):
+      def cat(inputs, outputs):
            return 'cat {} > {}'.format(inputs[0].filepath, outputs[0].filepath)
 
 
@@ -409,16 +409,16 @@ New Functionality
 
         # The following example worked until v0.8.0
         @bash_app
-        def cat(inputs=(), outputs=()):
+        def cat(inputs, outputs):
             return 'cat {inputs[0]} > {outputs[0]}' # <-- Relies on Parsl auto formatting the string
 
         # Following are two mechanisms that will work going forward from v0.9.0
         @bash_app
-        def cat(inputs=(), outputs=()):
+        def cat(inputs, outputs):
             return 'cat {} > {}'.format(inputs[0], outputs[0]) # <-- Use str.format method
 
         @bash_app
-        def cat(inputs=(), outputs=()):
+        def cat(inputs, outputs):
             return f'cat {inputs[0]} > {outputs[0]}' # <-- OR use f-strings introduced in Python3.6
 
 
@@ -522,12 +522,12 @@ New Functionality
 
      # Old style: " ".join(inputs) is legal since inputs will behave like a list of strings
      @bash_app
-     def concat(inputs=(), outputs=(), stdout="stdout.txt", stderr='stderr.txt'):
+     def concat(inputs, outputs, stdout="stdout.txt", stderr='stderr.txt'):
          return "cat {0} > {1}".format(" ".join(inputs), outputs[0])
 
      # New style:
      @bash_app
-     def concat(inputs=(), outputs=(), stdout="stdout.txt", stderr='stderr.txt'):
+     def concat(inputs, outputs, stdout="stdout.txt", stderr='stderr.txt'):
          return "cat {0} > {1}".format(" ".join(list(map(str,inputs))), outputs[0])
 
 * Cleaner user app file log management.
diff --git a/docs/userguide/apps/python.rst b/docs/userguide/apps/python.rst
index 00fac2ac30..666af9fa28 100644
--- a/docs/userguide/apps/python.rst
+++ b/docs/userguide/apps/python.rst
@@ -196,7 +196,7 @@ Some keyword arguments to the Python function are treated differently by Parsl
         return x * 2
 
     @python_app()
-    def reduce_app(inputs = ()):
+    def reduce_app(inputs):
         return sum(inputs)
 
     map_futures = [map_app(x) for x in range(3)]
@@ -212,7 +212,7 @@ Some keyword arguments to the Python function are treated differently by Parsl
 .. code-block:: python
 
     @python_app()
-    def write_app(message, outputs=()):
+    def write_app(message, outputs):
         """Write a single message to every file in outputs"""
         for path in outputs:
             with open(path, 'w') as fp:
diff --git a/docs/userguide/configuration/data.rst b/docs/userguide/configuration/data.rst
index 0c4c4b334d..9b3cdceacb 100644
--- a/docs/userguide/configuration/data.rst
+++ b/docs/userguide/configuration/data.rst
@@ -67,7 +67,7 @@ irrespective of where that app executes.
 .. code-block:: python
 
     @python_app
-    def print_file(inputs=()):
+    def print_file(inputs):
         with open(inputs[0].filepath, 'r') as inp:
             content = inp.read()
             return(content)
@@ -189,7 +189,7 @@ The following example illustrates how the remote file is implicitly downloaded f
 .. code-block:: python
 
     @python_app
-    def convert(inputs=(), outputs=()):
+    def convert(inputs, outputs):
         with open(inputs[0].filepath, 'r') as inp:
             content = inp.read()
             with open(outputs[0].filepath, 'w') as out:
diff --git a/docs/userguide/configuration/execution.rst b/docs/userguide/configuration/execution.rst
index ac7217032a..d4979dcd0c 100644
--- a/docs/userguide/configuration/execution.rst
+++ b/docs/userguide/configuration/execution.rst
@@ -216,12 +216,12 @@ The following code snippet shows how apps can specify suitable executors in the
 
      # A mock molecular dynamics simulation app
      @bash_app(executors=["Theta.Phi"])
-     def MD_Sim(arg, outputs=()):
+     def MD_Sim(arg, outputs):
          return "MD_simulate {} -o {}".format(arg, outputs[0])
 
      # Visualize results from the mock MD simulation app
      @bash_app(executors=["Cooley.GPU"])
-     def visualize(inputs=(), outputs=()):
+     def visualize(inputs, outputs):
          bash_array = " ".join(inputs)
          return "viz {} -o {}".format(bash_array, outputs[0])
 
diff --git a/docs/userguide/workflows/futures.rst b/docs/userguide/workflows/futures.rst
index 13d22a211b..50d342b5ec 100644
--- a/docs/userguide/workflows/futures.rst
+++ b/docs/userguide/workflows/futures.rst
@@ -151,7 +151,7 @@ be created (``hello.outputs[0].result()``).
       # This app echoes the input string to the first file specified in the
       # outputs list
       @bash_app
-      def echo(message, outputs=()):
+      def echo(message, outputs):
           return 'echo {} &> {}'.format(message, outputs[0])
 
       # Call echo specifying the output file
diff --git a/docs/userguide/workflows/workflow.rst b/docs/userguide/workflows/workflow.rst
index f8b34fa6c5..b67dd6cc2b 100644
--- a/docs/userguide/workflows/workflow.rst
+++ b/docs/userguide/workflows/workflow.rst
@@ -63,7 +63,7 @@ Sequential workflows can be created by passing an AppFuture from one task to ano
 
       # Write a message to a file
       @bash_app
-      def save(message, outputs=()):
+      def save(message, outputs):
             return 'echo {} &> {}'.format(message, outputs[0])
 
       message = generate(10)
@@ -159,15 +159,15 @@ In other cases, it can be convenient to pass data in files, as in the following
       parsl.load()
 			
       @bash_app
-      def generate(outputs=()):
+      def generate(outputs):
           return 'echo $(( RANDOM % (10 - 5 + 1 ) + 5 )) &> {}'.format(outputs[0])
 
       @bash_app
-      def concat(inputs=(), outputs=(), stdout='stdout.txt', stderr='stderr.txt'):
+      def concat(inputs, outputs, stdout='stdout.txt', stderr='stderr.txt'):
           return 'cat {0} >> {1}'.format(' '.join(inputs), outputs[0])
 
       @python_app
-      def total(inputs=()):
+      def total(inputs):
           total = 0
           with open(inputs[0].filepath, 'r') as f:
               for l in f:
@@ -209,7 +209,7 @@ the sum of those results.
 
     # Reduce function that returns the sum of a list
     @python_app
-    def app_sum(inputs=()):
+    def app_sum(inputs):
         return sum(inputs)
 
     # Create a list of integers
diff --git a/parsl/app/bash.py b/parsl/app/bash.py
index 36212c172f..06104a7a32 100644
--- a/parsl/app/bash.py
+++ b/parsl/app/bash.py
@@ -96,7 +96,7 @@ def open_std_fd(fdname):
     # TODO : Add support for globs here
 
     missing = []
-    for outputfile in kwargs.get('outputs', []):
+    for outputfile in kwargs.get('outputs') or []:
         fpath = outputfile.filepath
 
         if not os.path.exists(fpath):
diff --git a/parsl/data_provider/ftp.py b/parsl/data_provider/ftp.py
index 88cefe612c..9d50380716 100644
--- a/parsl/data_provider/ftp.py
+++ b/parsl/data_provider/ftp.py
@@ -66,7 +66,7 @@ def wrapper(*args, **kwargs):
     return wrapper
 
 
-def _ftp_stage_in(working_dir, parent_fut=None, outputs=[], _parsl_staging_inhibit=True):
+def _ftp_stage_in(working_dir, *, parent_fut=None, outputs, _parsl_staging_inhibit=True):
     file = outputs[0]
     if working_dir:
         os.makedirs(working_dir, exist_ok=True)
diff --git a/parsl/data_provider/globus.py b/parsl/data_provider/globus.py
index e63b0aa82f..f60a5c2514 100644
--- a/parsl/data_provider/globus.py
+++ b/parsl/data_provider/globus.py
@@ -267,7 +267,7 @@ def _update_local_path(self, file, executor, dfk):
 # this cannot be a class method, but must be a function, because I want
 # to be able to use partial() on it - and partial() does not work on
 # class methods
-def _globus_stage_in(provider, executor, parent_fut=None, outputs=[], _parsl_staging_inhibit=True):
+def _globus_stage_in(provider, executor, *, parent_fut=None, outputs, _parsl_staging_inhibit=True):
     globus_ep = provider._get_globus_endpoint(executor)
     file = outputs[0]
     dst_path = os.path.join(
@@ -280,7 +280,7 @@ def _globus_stage_in(provider, executor, parent_fut=None, outputs=[], _parsl_sta
             file.path, dst_path)
 
 
-def _globus_stage_out(provider, executor, app_fu, inputs=[], _parsl_staging_inhibit=True):
+def _globus_stage_out(provider, executor, *, app_fu, inputs, _parsl_staging_inhibit=True):
     """
     Although app_fu isn't directly used in the stage out code,
     it is needed as an input dependency to ensure this code
diff --git a/parsl/data_provider/http.py b/parsl/data_provider/http.py
index 4553839ba8..6c3c7128bd 100644
--- a/parsl/data_provider/http.py
+++ b/parsl/data_provider/http.py
@@ -73,7 +73,7 @@ def wrapper(*args, **kwargs):
     return wrapper
 
 
-def _http_stage_in(working_dir, parent_fut=None, outputs=[], _parsl_staging_inhibit=True):
+def _http_stage_in(working_dir, *, parent_fut=None, outputs, _parsl_staging_inhibit=True):
     file = outputs[0]
     if working_dir:
         os.makedirs(working_dir, exist_ok=True)
diff --git a/parsl/data_provider/zip.py b/parsl/data_provider/zip.py
index 167ddbbdf7..fbcd2b1c4f 100644
--- a/parsl/data_provider/zip.py
+++ b/parsl/data_provider/zip.py
@@ -96,7 +96,7 @@ def stage_in(self, dm, executor, file, parent_fut):
         return app_fut._outputs[0]
 
 
-def _zip_stage_out(zip_file, inside_path, working_dir, parent_fut=None, inputs=[], _parsl_staging_inhibit=True):
+def _zip_stage_out(zip_file, inside_path, working_dir, *, parent_fut=None, inputs, _parsl_staging_inhibit=True):
     file = inputs[0]
 
     os.makedirs(os.path.dirname(zip_file), exist_ok=True)
diff --git a/parsl/dataflow/dflow.py b/parsl/dataflow/dflow.py
index 5e91268057..9e22cb7c9c 100644
--- a/parsl/dataflow/dflow.py
+++ b/parsl/dataflow/dflow.py
@@ -782,7 +782,7 @@ def _add_input_deps(self, executor: str, args: Sequence[Any], kwargs: Dict[str,
             logger.debug("Not performing input staging")
             return args, kwargs, func
 
-        inputs = kwargs.get('inputs', [])
+        inputs = kwargs.get('inputs') or []
         for idx, f in enumerate(inputs):
             (inputs[idx], func) = self.data_manager.optionally_stage_in(f, func, executor)
 
@@ -801,7 +801,7 @@ def _add_input_deps(self, executor: str, args: Sequence[Any], kwargs: Dict[str,
 
     def _add_output_deps(self, executor: str, args: Sequence[Any], kwargs: Dict[str, Any], app_fut: AppFuture, func: Callable) -> Callable:
         logger.debug("Adding output dependencies")
-        outputs = kwargs.get('outputs', [])
+        outputs = kwargs.get('outputs') or []
         app_fut._outputs = []
 
         # Pass over all possible outputs: the outputs kwarg, stdout and stderr
@@ -884,7 +884,7 @@ def check_dep(d: Any) -> None:
             check_dep(dep)
 
         # Check for futures in inputs=[<fut>...]
-        for dep in kwargs.get('inputs', []):
+        for dep in kwargs.get('inputs') or []:
             check_dep(dep)
 
         return depends
@@ -932,7 +932,7 @@ def append_failure(e: Exception, dep: Future) -> None:
                 append_failure(e, dep)
 
         # Check for futures in inputs=[<fut>...]
-        if 'inputs' in kwargs:
+        if kwargs.get('inputs'):
             new_inputs = []
             for dep in kwargs['inputs']:
                 try:
diff --git a/parsl/dataflow/memoization.py b/parsl/dataflow/memoization.py
index 551bd0b9d4..facff16a33 100644
--- a/parsl/dataflow/memoization.py
+++ b/parsl/dataflow/memoization.py
@@ -191,7 +191,7 @@ def make_hash(self, task: TaskRecord) -> str:
             logger.debug("Ignoring kwarg %s", k)
             del filtered_kw[k]
 
-        if 'outputs' in task['kwargs']:
+        if task['kwargs'].get('outputs'):
             outputs = task['kwargs']['outputs']
             del filtered_kw['outputs']
             t.append(id_for_memo(outputs, output_ref=True))
diff --git a/parsl/executors/radical/executor.py b/parsl/executors/radical/executor.py
index aa191f49e5..184f0b031a 100644
--- a/parsl/executors/radical/executor.py
+++ b/parsl/executors/radical/executor.py
@@ -422,9 +422,9 @@ def task_translate(self, tid, func, parsl_resource_specification, args, kwargs):
                 task.use_mpi = False
                 task.function = self._pack_and_apply_message(func, args, kwargs)
 
-        task.input_staging = self._stage_files(kwargs.get("inputs", []),
+        task.input_staging = self._stage_files(kwargs.get("inputs") or [],
                                                mode='in')
-        task.output_staging = self._stage_files(kwargs.get("outputs", []),
+        task.output_staging = self._stage_files(kwargs.get("outputs") or [],
                                                 mode='out')
 
         task.input_staging.extend(self._stage_files(list(args), mode='in'))
diff --git a/parsl/executors/taskvine/executor.py b/parsl/executors/taskvine/executor.py
index 5896d333b5..c182a4c0fe 100644
--- a/parsl/executors/taskvine/executor.py
+++ b/parsl/executors/taskvine/executor.py
@@ -360,8 +360,8 @@ def submit(self, func, resource_specification, *args, **kwargs):
 
         # Determine whether to stage input files that will exist at the workers
         # Input and output files are always cached
-        input_files += [self._register_file(f) for f in kwargs.get("inputs", []) if isinstance(f, File)]
-        output_files += [self._register_file(f) for f in kwargs.get("outputs", []) if isinstance(f, File)]
+        input_files += [self._register_file(f) for f in kwargs.get("inputs") or [] if isinstance(f, File)]
+        output_files += [self._register_file(f) for f in kwargs.get("outputs") or [] if isinstance(f, File)]
 
         # Also consider any *arg that looks like a file as an input:
         input_files += [self._register_file(f) for f in args if isinstance(f, File)]
diff --git a/parsl/executors/taskvine/install-taskvine.sh b/parsl/executors/taskvine/install-taskvine.sh
index cabd253770..ab5adc9c46 100755
--- a/parsl/executors/taskvine/install-taskvine.sh
+++ b/parsl/executors/taskvine/install-taskvine.sh
@@ -12,7 +12,7 @@ TARBALL="cctools-$CCTOOLS_VERSION-x86_64-ubuntu20.04.tar.gz"
 
 # If stderr is *not* a TTY, then disable progress bar and show HTTP response headers
 [[ ! -t 1 ]] && NO_VERBOSE="--no-verbose" SHOW_HEADERS="-S"
-wget "$NO_VERBOSE" "$SHOW_HEADERS" -O /tmp/cctools.tar.gz "https://github.com/cooperative-computing-lab/cctools/releases/download/release/$CCTOOLS_VERSION/$TARBALL"
+wget $NO_VERBOSE $SHOW_HEADERS -O /tmp/cctools.tar.gz "https://github.com/cooperative-computing-lab/cctools/releases/download/release/$CCTOOLS_VERSION/$TARBALL"
 
 mkdir -p /tmp/cctools
 tar -C /tmp/cctools -zxf /tmp/cctools.tar.gz --strip-components=1
diff --git a/parsl/executors/workqueue/executor.py b/parsl/executors/workqueue/executor.py
index b1a534623e..967320bc9d 100644
--- a/parsl/executors/workqueue/executor.py
+++ b/parsl/executors/workqueue/executor.py
@@ -461,8 +461,8 @@ def submit(self, func, resource_specification, *args, **kwargs):
         output_files = []
 
         # Determine the input and output files that will exist at the workers:
-        input_files += [self._register_file(f) for f in kwargs.get("inputs", []) if isinstance(f, File)]
-        output_files += [self._register_file(f) for f in kwargs.get("outputs", []) if isinstance(f, File)]
+        input_files += [self._register_file(f) for f in kwargs.get("inputs") or [] if isinstance(f, File)]
+        output_files += [self._register_file(f) for f in kwargs.get("outputs") or [] if isinstance(f, File)]
 
         # Also consider any *arg that looks like a file as an input:
         input_files += [self._register_file(f) for f in args if isinstance(f, File)]
diff --git a/parsl/tests/integration/test_parsl_load_default_config.py b/parsl/tests/integration/test_parsl_load_default_config.py
index bb9446c4cd..063162112f 100644
--- a/parsl/tests/integration/test_parsl_load_default_config.py
+++ b/parsl/tests/integration/test_parsl_load_default_config.py
@@ -3,7 +3,7 @@
 
 
 @python_app
-def cpu_stress(inputs=[], outputs=[]):
+def cpu_stress(inputs=None, outputs=None):
     s = 0
     for i in range(10**8):
         s += i
diff --git a/parsl/tests/test_aalst_patterns.py b/parsl/tests/test_aalst_patterns.py
index e410a7243a..8ba4bd9deb 100644
--- a/parsl/tests/test_aalst_patterns.py
+++ b/parsl/tests/test_aalst_patterns.py
@@ -76,7 +76,7 @@ def slow_increment(x, dur=1):
 
 
 @python_app
-def join(inputs=[]):
+def join(inputs):
     return sum(inputs)
 
 
diff --git a/parsl/tests/test_bash_apps/test_apptimeout.py b/parsl/tests/test_bash_apps/test_apptimeout.py
index 1c8eebaf5e..fd8c5b18ad 100644
--- a/parsl/tests/test_bash_apps/test_apptimeout.py
+++ b/parsl/tests/test_bash_apps/test_apptimeout.py
@@ -7,7 +7,7 @@
 
 
 @bash_app
-def echo_to_file(inputs=(), outputs=(), walltime=0.01):
+def echo_to_file(inputs=None, outputs=None, walltime=0.01):
     return """echo "sleeping"; sleep 0.05"""
 
 
diff --git a/parsl/tests/test_bash_apps/test_basic.py b/parsl/tests/test_bash_apps/test_basic.py
index 0eea6d4d97..9da4b8c6e4 100644
--- a/parsl/tests/test_bash_apps/test_basic.py
+++ b/parsl/tests/test_bash_apps/test_basic.py
@@ -11,7 +11,7 @@
 
 
 @bash_app
-def echo_to_file(inputs=(), outputs=(), stderr=None, stdout=None):
+def echo_to_file(inputs, outputs, stderr=None, stdout=None):
     res = ""
     for o in outputs:
         for i in inputs:
diff --git a/parsl/tests/test_bash_apps/test_memoize.py b/parsl/tests/test_bash_apps/test_memoize.py
index 387837f4d2..0157036208 100644
--- a/parsl/tests/test_bash_apps/test_memoize.py
+++ b/parsl/tests/test_bash_apps/test_memoize.py
@@ -5,7 +5,7 @@
 
 
 @bash_app(cache=True)
-def fail_on_presence(outputs=()):
+def fail_on_presence(outputs):
     return 'if [ -f {0} ] ; then exit 1 ; else touch {0}; fi'.format(outputs[0])
 
 
@@ -23,7 +23,7 @@ def test_bash_memoization(tmpd_cwd, n=2):
 
 
 @bash_app(cache=True)
-def fail_on_presence_kw(outputs=(), foo=None):
+def fail_on_presence_kw(outputs, foo=None):
     return 'if [ -f {0} ] ; then exit 1 ; else touch {0}; fi'.format(outputs[0])
 
 
diff --git a/parsl/tests/test_bash_apps/test_multiline.py b/parsl/tests/test_bash_apps/test_multiline.py
index cfdb674e9d..cc67934dc4 100644
--- a/parsl/tests/test_bash_apps/test_multiline.py
+++ b/parsl/tests/test_bash_apps/test_multiline.py
@@ -5,7 +5,7 @@
 
 
 @bash_app
-def multiline(inputs=(), outputs=(), stderr=None, stdout=None):
+def multiline(inputs, outputs, stderr=None, stdout=None):
     return """echo {inputs[0]} &> {outputs[0]}
     echo {inputs[1]} &> {outputs[1]}
     echo {inputs[2]} &> {outputs[2]}
diff --git a/parsl/tests/test_bash_apps/test_pipeline.py b/parsl/tests/test_bash_apps/test_pipeline.py
index 75f16237d8..8df3d63de4 100644
--- a/parsl/tests/test_bash_apps/test_pipeline.py
+++ b/parsl/tests/test_bash_apps/test_pipeline.py
@@ -6,7 +6,7 @@
 
 
 @bash_app
-def increment(inputs=(), outputs=(), stdout=None, stderr=None):
+def increment(inputs, outputs, stdout=None, stderr=None):
     cmd_line = """
     if ! [ -f {inputs[0]} ] ; then exit 43 ; fi
     x=$(cat {inputs[0]})
@@ -16,7 +16,7 @@ def increment(inputs=(), outputs=(), stdout=None, stderr=None):
 
 
 @bash_app
-def slow_increment(dur, inputs=(), outputs=(), stdout=None, stderr=None):
+def slow_increment(dur, inputs, outputs, stdout=None, stderr=None):
     cmd_line = """
     x=$(cat {inputs[0]})
     echo $(($x+1)) > {outputs[0]}
diff --git a/parsl/tests/test_docs/test_from_slides.py b/parsl/tests/test_docs/test_from_slides.py
index b3242e813e..a9038d8fa6 100644
--- a/parsl/tests/test_docs/test_from_slides.py
+++ b/parsl/tests/test_docs/test_from_slides.py
@@ -7,12 +7,12 @@
 
 
 @bash_app
-def echo(message, outputs=[]):
+def echo(message, outputs):
     return 'echo {m} &> {o}'.format(m=message, o=outputs[0])
 
 
 @python_app
-def cat(inputs=[]):
+def cat(inputs):
     with open(inputs[0].filepath) as f:
         return f.readlines()
 
diff --git a/parsl/tests/test_docs/test_kwargs.py b/parsl/tests/test_docs/test_kwargs.py
index 80907ebe08..ab412a55a4 100644
--- a/parsl/tests/test_docs/test_kwargs.py
+++ b/parsl/tests/test_docs/test_kwargs.py
@@ -12,7 +12,7 @@ def map_app(x):
         return x * 2
 
     @python_app()
-    def reduce_app(inputs=()):
+    def reduce_app(inputs):
         return sum(inputs)
 
     map_futures = [map_app(x) for x in range(3)]
@@ -24,7 +24,7 @@ def reduce_app(inputs=()):
 @pytest.mark.shared_fs
 def test_outputs(tmpd_cwd):
     @python_app()
-    def write_app(message, outputs=()):
+    def write_app(message, outputs):
         """Write a single message to every file in outputs"""
         for path in outputs:
             with open(path, 'w') as fp:
diff --git a/parsl/tests/test_docs/test_tutorial_1.py b/parsl/tests/test_docs/test_tutorial_1.py
index cffc03e33d..5499d1abf9 100644
--- a/parsl/tests/test_docs/test_tutorial_1.py
+++ b/parsl/tests/test_docs/test_tutorial_1.py
@@ -10,7 +10,7 @@
 
 
 @bash_app
-def sim_mol_dyn(i, dur, outputs=[], stdout=None, stderr=None):
+def sim_mol_dyn(i, dur, outputs, stdout=None, stderr=None):
     # The bash app function, requires that the bash script is assigned to the special variable
     # cmd_line. Positional and Keyword args to the fn() are formatted into the cmd_line string
     cmd_line = """echo "{0}" > {outputs[0]}
diff --git a/parsl/tests/test_docs/test_workflow1.py b/parsl/tests/test_docs/test_workflow1.py
index 271baab4d8..bda5b74156 100644
--- a/parsl/tests/test_docs/test_workflow1.py
+++ b/parsl/tests/test_docs/test_workflow1.py
@@ -18,7 +18,7 @@ def generate(limit):
 
 
 @bash_app
-def save(message, outputs=[]):
+def save(message, outputs):
     return 'echo {m} &> {o}'.format(m=message, o=outputs[0])
 
 
diff --git a/parsl/tests/test_docs/test_workflow4.py b/parsl/tests/test_docs/test_workflow4.py
index 05a2a6f809..0641b3bb63 100644
--- a/parsl/tests/test_docs/test_workflow4.py
+++ b/parsl/tests/test_docs/test_workflow4.py
@@ -5,17 +5,17 @@
 
 
 @bash_app
-def generate(outputs=()):
+def generate(outputs):
     return "echo 1 &> {o}".format(o=outputs[0])
 
 
 @bash_app
-def concat(inputs=(), outputs=(), stdout=None, stderr=None):
+def concat(inputs, outputs, stdout=None, stderr=None):
     return "cat {0} >> {1}".format(" ".join(map(lambda x: x.filepath, inputs)), outputs[0])
 
 
 @python_app
-def total(inputs=()):
+def total(inputs):
     with open(inputs[0].filepath, "r") as f:
         return sum(int(line) for line in f)
 
diff --git a/parsl/tests/test_error_handling/test_rand_fail.py b/parsl/tests/test_error_handling/test_rand_fail.py
index 4046b8ffb6..b6b0642bd0 100644
--- a/parsl/tests/test_error_handling/test_rand_fail.py
+++ b/parsl/tests/test_error_handling/test_rand_fail.py
@@ -14,7 +14,7 @@ def local_config():
 
 
 @python_app
-def sleep_fail(sleep_dur, sleep_rand_max, fail_prob, inputs=[]):
+def sleep_fail(sleep_dur, sleep_rand_max, fail_prob, inputs=None):
     import random
     import time
 
diff --git a/parsl/tests/test_error_handling/test_retries.py b/parsl/tests/test_error_handling/test_retries.py
index 06ae81702e..4ef32e86c9 100644
--- a/parsl/tests/test_error_handling/test_retries.py
+++ b/parsl/tests/test_error_handling/test_retries.py
@@ -13,7 +13,7 @@ def local_config():
 
 
 @python_app
-def sleep_then_fail(inputs=[], sleep_dur=0.1):
+def sleep_then_fail(inputs=None, sleep_dur=0.1):
     import math
     import time
     time.sleep(sleep_dur)
diff --git a/parsl/tests/test_monitoring/test_incomplete_futures.py b/parsl/tests/test_monitoring/test_incomplete_futures.py
index c73d973150..796f011fc1 100644
--- a/parsl/tests/test_monitoring/test_incomplete_futures.py
+++ b/parsl/tests/test_monitoring/test_incomplete_futures.py
@@ -9,7 +9,7 @@
 
 
 @parsl.python_app
-def this_app(inputs=()):
+def this_app(inputs):
     return inputs[0]
 
 
diff --git a/parsl/tests/test_python_apps/test_arg_input_types.py b/parsl/tests/test_python_apps/test_arg_input_types.py
index 1149705ec1..3219d45def 100644
--- a/parsl/tests/test_python_apps/test_arg_input_types.py
+++ b/parsl/tests/test_python_apps/test_arg_input_types.py
@@ -7,12 +7,12 @@
 
 
 @python_app
-def take_a_value(inputs=[]):
+def take_a_value(inputs):
     return str(inputs[0])
 
 
 @python_app
-def add_two_values(inputs=[]):
+def add_two_values(inputs):
     return inputs[0] + inputs[1]
 
 
diff --git a/parsl/tests/test_python_apps/test_fail.py b/parsl/tests/test_python_apps/test_fail.py
index a310c2f131..99407312de 100644
--- a/parsl/tests/test_python_apps/test_fail.py
+++ b/parsl/tests/test_python_apps/test_fail.py
@@ -9,7 +9,7 @@ class ManufacturedTestFailure(Exception):
 
 
 @python_app
-def random_fail(fail_prob: float, inputs=()):
+def random_fail(fail_prob: float, inputs=None):
     import random
     if random.random() < fail_prob:
         raise ManufacturedTestFailure("App failure")
diff --git a/parsl/tests/test_python_apps/test_futures.py b/parsl/tests/test_python_apps/test_futures.py
index 500845f73b..a2e8cb7e65 100644
--- a/parsl/tests/test_python_apps/test_futures.py
+++ b/parsl/tests/test_python_apps/test_futures.py
@@ -20,7 +20,7 @@
 
 
 @python_app
-def delay_incr(x, delay=0.0, outputs=()):
+def delay_incr(x, delay=0.0, outputs=None):
     import time
     if outputs:
         with open(outputs[0].filepath, 'w') as outs:
diff --git a/parsl/tests/test_python_apps/test_mapred.py b/parsl/tests/test_python_apps/test_mapred.py
index 1c22334c4f..05d8e7f7f8 100644
--- a/parsl/tests/test_python_apps/test_mapred.py
+++ b/parsl/tests/test_python_apps/test_mapred.py
@@ -9,7 +9,7 @@ def times_two(x):
 
 
 @python_app
-def accumulate(inputs=()):
+def accumulate(inputs):
     return sum(inputs)
 
 
diff --git a/parsl/tests/test_python_apps/test_memoize_bad_id_for_memo.py b/parsl/tests/test_python_apps/test_memoize_bad_id_for_memo.py
index d423545773..441829954f 100644
--- a/parsl/tests/test_python_apps/test_memoize_bad_id_for_memo.py
+++ b/parsl/tests/test_python_apps/test_memoize_bad_id_for_memo.py
@@ -25,7 +25,7 @@ def failing_memoizer(v, output_ref=False):
 
 
 @python_app(cache=True)
-def noop_app(x, inputs=[], cache=True):
+def noop_app(x, inputs=None, cache=True):
     return None
 
 
diff --git a/parsl/tests/test_python_apps/test_outputs.py b/parsl/tests/test_python_apps/test_outputs.py
index b4273cf286..0c5cfda51a 100644
--- a/parsl/tests/test_python_apps/test_outputs.py
+++ b/parsl/tests/test_python_apps/test_outputs.py
@@ -7,7 +7,7 @@
 
 
 @python_app
-def double(x, outputs=[]):
+def double(x, outputs):
     with open(outputs[0], 'w') as f:
         f.write(x * 5)
     return x * 5
diff --git a/parsl/tests/test_python_apps/test_overview.py b/parsl/tests/test_python_apps/test_overview.py
index 63e205efee..db30b67376 100644
--- a/parsl/tests/test_python_apps/test_overview.py
+++ b/parsl/tests/test_python_apps/test_overview.py
@@ -7,7 +7,7 @@ def app_double(x):
 
 
 @python_app
-def app_sum(inputs=()):
+def app_sum(inputs):
     return sum(inputs)
 
 
diff --git a/parsl/tests/test_regression/test_69a.py b/parsl/tests/test_regression/test_69a.py
index fa6fbb4116..e991df9bae 100644
--- a/parsl/tests/test_regression/test_69a.py
+++ b/parsl/tests/test_regression/test_69a.py
@@ -10,7 +10,7 @@
 
 
 @bash_app
-def echo_slow_message(msg, sleep=0, fu=None, outputs=[], stderr='std.err', stdout='std.out'):
+def echo_slow_message(msg, *, sleep=0, fu=None, outputs, stderr='std.err', stdout='std.out'):
     cmd_line = 'sleep {sleep}; echo {0} > {outputs[0]}'
     return cmd_line
 
diff --git a/parsl/tests/test_scaling/test_scale_down.py b/parsl/tests/test_scaling/test_scale_down.py
index a53630374f..e5de233ce6 100644
--- a/parsl/tests/test_scaling/test_scale_down.py
+++ b/parsl/tests/test_scaling/test_scale_down.py
@@ -41,7 +41,7 @@ def local_config():
 
 
 @python_app
-def waiting_app(ident: int, inputs=(), outputs=()):
+def waiting_app(ident: int, inputs=None, outputs=None):
     import pathlib
     import time
 
diff --git a/parsl/tests/test_scaling/test_scale_down_htex_auto_scale.py b/parsl/tests/test_scaling/test_scale_down_htex_auto_scale.py
index 831bdf82af..ab440bb5df 100644
--- a/parsl/tests/test_scaling/test_scale_down_htex_auto_scale.py
+++ b/parsl/tests/test_scaling/test_scale_down_htex_auto_scale.py
@@ -39,7 +39,7 @@ def local_config():
 
 
 @python_app
-def waiting_app(ident: int, outputs=(), inputs=()):
+def waiting_app(ident: int, outputs, inputs):
     import pathlib
     import time
 
diff --git a/parsl/tests/test_staging/staging_provider.py b/parsl/tests/test_staging/staging_provider.py
index d309e8d305..06b7069f9e 100644
--- a/parsl/tests/test_staging/staging_provider.py
+++ b/parsl/tests/test_staging/staging_provider.py
@@ -61,7 +61,7 @@ def make_stage_out_app(executor, dfk):
     return python_app(executors=[executor], data_flow_kernel=dfk)(stage_out_noop)
 
 
-def stage_out_noop(app_fu, inputs=[], _parsl_staging_inhibit=True):
+def stage_out_noop(app_fu, inputs=None, _parsl_staging_inhibit=True):
     import logging
     import time
     logger = logging.getLogger(__name__)
@@ -74,7 +74,7 @@ def make_stage_in_app(executor, dfk):
     return python_app(executors=[executor], data_flow_kernel=dfk)(stage_in_noop)
 
 
-def stage_in_noop(parent_fut=None, outputs=[], _parsl_staging_inhibit=True):
+def stage_in_noop(parent_fut=None, outputs=None, _parsl_staging_inhibit=True):
     import logging
     import time
     logger = logging.getLogger(__name__)
diff --git a/parsl/tests/test_staging/test_1316.py b/parsl/tests/test_staging/test_1316.py
index 9d5b7a33b2..7bbbae02e8 100644
--- a/parsl/tests/test_staging/test_1316.py
+++ b/parsl/tests/test_staging/test_1316.py
@@ -18,7 +18,7 @@ def observe_input_local_path(f):
 
 
 @python_app
-def wait_and_create(outputs=[]):
+def wait_and_create(outputs=None):
     # for test purposes, this doesn't actually need to create the output
     # file as nothing ever touches file content - the test only deals with
     # names and Futures.
diff --git a/parsl/tests/test_staging/test_docs_1.py b/parsl/tests/test_staging/test_docs_1.py
index c4f0e3b007..cbbecf76e9 100644
--- a/parsl/tests/test_staging/test_docs_1.py
+++ b/parsl/tests/test_staging/test_docs_1.py
@@ -4,7 +4,7 @@
 
 
 @python_app
-def convert(inputs=[], outputs=[]):
+def convert(inputs, outputs):
     with open(inputs[0].filepath, 'r') as inp:
         content = inp.read()
         with open(outputs[0].filepath, 'w') as out:
diff --git a/parsl/tests/test_staging/test_docs_2.py b/parsl/tests/test_staging/test_docs_2.py
index a985872bce..33723a476d 100644
--- a/parsl/tests/test_staging/test_docs_2.py
+++ b/parsl/tests/test_staging/test_docs_2.py
@@ -5,7 +5,7 @@
 
 
 @bash_app
-def cat(inputs=[], stdout='stdout.txt'):
+def cat(inputs, stdout='stdout.txt'):
     return 'cat %s' % (inputs[0])
 
 
diff --git a/parsl/tests/test_staging/test_elaborate_noop_file.py b/parsl/tests/test_staging/test_elaborate_noop_file.py
index 6f52536059..ba3d6a413c 100644
--- a/parsl/tests/test_staging/test_elaborate_noop_file.py
+++ b/parsl/tests/test_staging/test_elaborate_noop_file.py
@@ -20,7 +20,7 @@
 
 
 @bash_app
-def touch(filename, outputs=()):
+def touch(filename, outputs=None):
     return f"touch {filename}"
 
 
@@ -51,7 +51,7 @@ def test_regression_stage_out_does_not_stage_in(storage_access_parsl, tmpd_cwd):
     storage_access_parsl(allow_stage_in=False)
 
     # Test that the helper app runs with no staging
-    touch(str(tmpd_cwd / "test.1"), outputs=[]).result()
+    touch(str(tmpd_cwd / "test.1"), outputs=None).result()
 
     # Test with stage-out, checking that provider stage-in is never
     # invoked. If stage-in is invoked, then the NoOpTestingFileStaging
diff --git a/parsl/tests/test_staging/test_file_apps.py b/parsl/tests/test_staging/test_file_apps.py
index fa56bb5457..345517775c 100644
--- a/parsl/tests/test_staging/test_file_apps.py
+++ b/parsl/tests/test_staging/test_file_apps.py
@@ -5,7 +5,7 @@
 
 
 @bash_app
-def cat(inputs=(), outputs=(), stdout=None, stderr=None):
+def cat(inputs, outputs, stdout=None, stderr=None):
     infiles = " ".join(i.filepath for i in inputs)
     return f"cat {infiles} &> {outputs[0]}"
 
@@ -27,7 +27,7 @@ def test_files(setup_data):
 
 
 @bash_app
-def increment(inputs=(), outputs=(), stdout=None, stderr=None):
+def increment(inputs, outputs, stdout=None, stderr=None):
     return (
         f"x=$(cat {inputs[0]})\n"
         f"echo $(($x+1)) > {outputs[0]}"
diff --git a/parsl/tests/test_staging/test_file_staging.py b/parsl/tests/test_staging/test_file_staging.py
index 4e3102c527..fead9cd8ef 100644
--- a/parsl/tests/test_staging/test_file_staging.py
+++ b/parsl/tests/test_staging/test_file_staging.py
@@ -5,7 +5,7 @@
 
 
 @bash_app
-def cat(inputs=(), outputs=(), stdout=None, stderr=None):
+def cat(inputs, outputs, stdout=None, stderr=None):
     infiles = " ".join(i.filepath for i in inputs)
     return f"cat {infiles} &> {outputs[0]}"
 
diff --git a/parsl/tests/test_staging/test_output_chain_filenames.py b/parsl/tests/test_staging/test_output_chain_filenames.py
index 442bd6fd5a..1a2e11563d 100644
--- a/parsl/tests/test_staging/test_output_chain_filenames.py
+++ b/parsl/tests/test_staging/test_output_chain_filenames.py
@@ -7,12 +7,12 @@
 
 
 @bash_app
-def app1(inputs=(), outputs=(), stdout=None, stderr=None, mock=False):
+def app1(outputs, inputs=None, stdout=None, stderr=None, mock=False):
     return f"echo 'test' > {outputs[0]}"
 
 
 @bash_app
-def app2(inputs=(), outputs=(), stdout=None, stderr=None, mock=False):
+def app2(inputs, outputs, stdout=None, stderr=None, mock=False):
     return f"echo '{inputs[0]}' > {outputs[0]}"
 
 
diff --git a/parsl/tests/test_staging/test_staging_ftp.py b/parsl/tests/test_staging/test_staging_ftp.py
index a004f5a575..66ba065597 100644
--- a/parsl/tests/test_staging/test_staging_ftp.py
+++ b/parsl/tests/test_staging/test_staging_ftp.py
@@ -5,7 +5,7 @@
 
 
 @python_app
-def sort_strings(inputs=[], outputs=[]):
+def sort_strings(inputs, outputs):
     with open(inputs[0].filepath, 'r') as u:
         strs = u.readlines()
         strs.sort()
diff --git a/parsl/tests/test_staging/test_staging_ftp_in_task.py b/parsl/tests/test_staging/test_staging_ftp_in_task.py
index da6a508bf2..1e36735f15 100644
--- a/parsl/tests/test_staging/test_staging_ftp_in_task.py
+++ b/parsl/tests/test_staging/test_staging_ftp_in_task.py
@@ -6,7 +6,7 @@
 
 
 @python_app
-def sort_strings(inputs=[], outputs=[]):
+def sort_strings(inputs, outputs):
     with open(inputs[0].filepath, 'r') as u:
         strs = u.readlines()
         strs.sort()
diff --git a/parsl/tests/test_staging/test_staging_globus.py b/parsl/tests/test_staging/test_staging_globus.py
index 37814175ad..4acf8e1bbf 100644
--- a/parsl/tests/test_staging/test_staging_globus.py
+++ b/parsl/tests/test_staging/test_staging_globus.py
@@ -9,7 +9,7 @@
 
 
 @python_app
-def sort_strings(inputs=[], outputs=[]):
+def sort_strings(inputs, outputs):
     with open(inputs[0].filepath, 'r') as u:
         strs = u.readlines()
         strs.sort()
diff --git a/parsl/tests/test_staging/test_staging_https.py b/parsl/tests/test_staging/test_staging_https.py
index c977472249..4000721bab 100644
--- a/parsl/tests/test_staging/test_staging_https.py
+++ b/parsl/tests/test_staging/test_staging_https.py
@@ -24,25 +24,25 @@
 
 
 @python_app
-def sort_strings(inputs=(), outputs=()):
+def sort_strings(inputs, outputs):
     from parsl.tests.test_staging import read_sort_write
     read_sort_write(inputs[0].filepath, outputs[0].filepath)
 
 
 @python_app
-def sort_strings_kw(*, x=None, outputs=()):
+def sort_strings_kw(*, x=None, outputs):
     from parsl.tests.test_staging import read_sort_write
     read_sort_write(x.filepath, outputs[0].filepath)
 
 
 @python_app
-def sort_strings_arg(x, /, outputs=()):
+def sort_strings_arg(x, /, outputs):
     from parsl.tests.test_staging import read_sort_write
     read_sort_write(x.filepath, outputs[0].filepath)
 
 
 @python_app(executors=['other'])
-def sort_strings_additional_executor(inputs=(), outputs=()):
+def sort_strings_additional_executor(inputs, outputs):
     from parsl.tests.test_staging import read_sort_write
     read_sort_write(inputs[0].filepath, outputs[0].filepath)
 
diff --git a/parsl/tests/test_staging/test_zip_out.py b/parsl/tests/test_staging/test_zip_out.py
index 79fbb504d5..7e51aea48d 100644
--- a/parsl/tests/test_staging/test_zip_out.py
+++ b/parsl/tests/test_staging/test_zip_out.py
@@ -20,7 +20,7 @@ def test_zip_path_split():
 
 
 @parsl.bash_app
-def output_something(outputs=()):
+def output_something(outputs):
     """This should output something into every specified output file:
     the position in the output sequence will be written into the
     corresponding output file.