With Parsl 0.8.0a, the tutorial fails in the Parallel Dataflow section (on both Ubuntu and MacOS):

@bash_app
def generate(outputs=[]):
    return "echo $(( RANDOM )) &> {outputs[0]}"

# App that concatenates input files into a single output file
@bash_app
def concat(inputs=[], outputs=[], stdout="stdout.txt", stderr='stderr.txt'):
    return "cat {0} > {1}".format(" ".join(inputs), outputs[0])

# App that calculates the sum of values in a list of input files
@python_app
def total(inputs=[]):
    total = 0
    with open(inputs[0], 'r') as f:
        for l in f:
            total += int(l)
    return total

# Create 5 files with random numbers
output_files = []
for i in range (5):
     output_files.append(generate(outputs=[os.path.join(os.getcwd(), 'random-{}.txt'.format(i))]))

# Concatenate the files into a single file
cc = concat(inputs=[i.outputs[0] for i in output_files], outputs=[os.path.join(os.getcwd(), 'all.txt')])

# Calculate the sum of the random numbers
total = total(inputs=[cc.outputs[0]])
print (total.result())

The error is:

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
/anaconda/lib/python3.6/site-packages/parsl/dataflow/dflow.py in sanitize_and_wrap(self, task_id, args, kwargs)
    579                     try:
--> 580                         new_inputs.extend([dep.result()])
    581                     except Exception as e:

/anaconda/lib/python3.6/concurrent/futures/_base.py in result(self, timeout)
    424             elif self._state == FINISHED:
--> 425                 return self.__get_result()
    426 

/anaconda/lib/python3.6/concurrent/futures/_base.py in __get_result(self)
    383         if self._exception:
--> 384             raise self._exception
    385         else:

/anaconda/lib/python3.6/site-packages/parsl/dataflow/futures.py in parent_callback(self, executor_fu)
    119                 if isinstance(res, RemoteExceptionWrapper):
--> 120                     res.reraise()
    121                 super().set_result(executor_fu.result())

/anaconda/lib/python3.6/site-packages/parsl/app/errors.py in reraise(self)
    162 
--> 163         reraise(t, v, tb)
    164 

/anaconda/lib/python3.6/site-packages/six.py in reraise(tp, value, tb)
    691             if value.__traceback__ is not tb:
--> 692                 raise value.with_traceback(tb)
    693             raise value

/anaconda/lib/python3.6/site-packages/parsl/app/errors.py in wrapper()
    171         try:
--> 172             return func(*args, **kwargs)
    173         except Exception:

/anaconda/lib/python3.6/site-packages/parsl/app/bash.py in remote_side_bash_executor()
     49         logging.error("Caught exception during formatting of app '{}': {}".format(func_name, e))
---> 50         raise e
     51 

/anaconda/lib/python3.6/site-packages/parsl/app/bash.py in remote_side_bash_executor()
     35         # Execute the func to get the commandline
---> 36         partial_cmdline = func(*args, **kwargs)
     37         # Reformat the commandline with current args and kwargs

<ipython-input-15-c2623b1950fb> in concat()
      8 def concat(inputs=[], outputs=[], stdout="stdout.txt", stderr='stderr.txt'):
----> 9     return "cat {0} > {1}".format(" ".join(inputs), outputs[0])
     10 

TypeError: sequence item 0: expected str instance, File found

During handling of the above exception, another exception occurred:

DependencyError                           Traceback (most recent call last)
<ipython-input-15-c2623b1950fb> in <module>()
     28 # Calculate the sum of the random numbers
     29 total = total(inputs=[cc.outputs[0]])
---> 30 print (total.result())

/anaconda/lib/python3.6/concurrent/futures/_base.py in result(self, timeout)
    430                 raise CancelledError()
    431             elif self._state == FINISHED:
--> 432                 return self.__get_result()
    433             else:
    434                 raise TimeoutError()

/anaconda/lib/python3.6/concurrent/futures/_base.py in __get_result(self)
    382     def __get_result(self):
    383         if self._exception:
--> 384             raise self._exception
    385         else:
    386             return self._result

/anaconda/lib/python3.6/site-packages/parsl/dataflow/futures.py in parent_callback(self, executor_fu)
    116 
    117             try:
--> 118                 res = executor_fu.result()
    119                 if isinstance(res, RemoteExceptionWrapper):
    120                     res.reraise()

/anaconda/lib/python3.6/concurrent/futures/_base.py in result(self, timeout)
    423                 raise CancelledError()
    424             elif self._state == FINISHED:
--> 425                 return self.__get_result()
    426 
    427             self._condition.wait(timeout)

/anaconda/lib/python3.6/concurrent/futures/_base.py in __get_result(self)
    382     def __get_result(self):
    383         if self._exception:
--> 384             raise self._exception
    385         else:
    386             return self._result

DependencyError: [23] Dependency failure from: [TypeError('sequence item 0: expected str instance, File found',)]```