Basic help understanding Python functions

Question

I'm trying to understand how functions work and have a basic question. I'm trying to figure out how to set a variable into the function and don't know how. Probably easier for me to show my code:

I have a bit of code that unzips a file

fh = open(fn, 'rb')
z = zipfile.ZipFile(fh)
for name in z.namelist():
    z.extract(name, outpath)
fh.close()

I can put this into a function by defining it as:

def extract_zip():
    fh = open(fn, 'rb')
    z = zipfile.ZipFile(fh)
    for name in z.namelist():
        z.extract(name, outpath)
    fh.close()

And then I can call it by typing:

extract_zip()

But the purpose of putting this into a function is so I can use it over and over again. But when I use it a 2nd or 3rd time, the variable name won't be 'fn' but rather another variable name defined later.

How can i write this function but define 'fn' as a variable and then call it later by typing

extract_zip(2nd_filename)

Thanks

Answer 1

This is as simple as puting fn as argument of your function

def extract_zip(fn):
    fh = open(fn, 'rb')
    z = zipfile.ZipFile(fh)
    for name in z.namelist():
        z.extract(name, outpath)
    fh.close()

Sometime, you may also want to use a default name

def extract_zip(fn="default_name.extension"):
    #...

Furthermore, note that your file name can be a full file name, which means that it can include the path to the file you want to read. For example, if your project layout is

your_working_direcory/
    your_script.py
    folder1/
        folder2/
            file_to_read.extension

you would have to define the full name of the file you want to read as

yourFullFileName = os.path.join(
                       os.path.dirname(__file__),# __file__ is the full name of your working script, 
                      'folder1', 
                      'folder2', 
                      'file_to_read.extension'
                   )

which ensures the portability of your script (you don't have to worry about the operating-system dependant separator, mainly). Then you would use your function like so

extract_zip(fn=yourFullFileName)

Answer 2

def extract_zip(name_of_file):
    fh = open(name_of_file, 'rb')
    z = zipfile.ZipFile(fh)
    for name in z.namelist():
        z.extract(name, outpath)
    fh.close()

The above allows you to set the name of the file as name_of_file='my filename'

Answer 3

To be able to reuse functions, you have to make the variable elements arguments to the function, eg:

def extract_zip(filename, outpath):
    with zipfile.ZipFile(filename) as z:
        z.extractall(outpath)
        return z.namelist()

The return returns alls the names of the archive objects, so that you can keep track of the items extracted.

files = {}
files[(filename, outpath)] = extract_zip('my.zip', 'output')

Answer 4

One Way You Can Change The Variable Is Add A input() Function (raw.input() for older Python versions)

var = input(What Is THe Filename? (Make It Exact!): )

var is whatever your variable is.