How to create user-defined function with Python list?

Question

This is the part of the code that I want to package into function. I tired this way

def mm(*files, writer=None):
    for file in files:
        if fnmatch.fnmatch(file, 'ticr_calculated_2*'):
            gunzip(file, file.replace(".gz", ""))

    json_fi = glob.glob("*.json")
    table_list=[]
    for filename in json_fi:
        with open(filename, encoding='utf-8', mode='r') as i:
            data = pd.read_json(i, lines=True)
            table_list.append(data)

    for table in table_list:
         writer = append_to_parquet_table(table, filepath, writer)

    if writer:
         writer.close()
    return writer

Latter I will have 'tick_calculated_3*' and similar file names.

I invoked my function

files = [fi for fi in files if fi.endswith(".gz")]
mm(files,writer)

Files are list type and it MUST stay that way.

I got error

  File "/usr/local/Cellar/python@3.8/3.8.3/Frameworks/Python.framework/Versions/3.8/lib/python3.8/posixpath.py", line 54, in normcase
    return os.fspath(s)
TypeError: expected str, bytes or os.PathLike object, not list

Answer 1

You can use * with your parameter which will catch any passed arguments in a tuple:

def f(*filenames):
    # filenames is a tuple with all your arguments and you can iteratore over
    print(type(filenames)) # prints <class 'tuple'>
    for arg in args:
       pass # do something here

If you would also want a positional argument (writer in your case), it must be placed as first parameter:

def f(writer, *filenames):
    print(writer)
    print(len(filenames)) # will be zero if only a writer is passed
    print(type(filenames))

In your case it's sufficient to use:

def mm(filenames): # you can pass anything that is iterable (list, tuples, strings, ...)
    for file in filenames: