# Accessing User Input

While building web applications, one basic and important thing is to respond to the user input that is sent to the server.

Web.py makes it easy to access that whether it is parameters in the url (GET request) or the form data (POST or PUT request). The web.input() method returns a dictionary-like object (more specifically a web.storage object) that contains the user input, whatever the request method is.

To access the URL parameters (?key=value) from the web.input object, just use web.input().key.

## GET

For a URL which looks like /page?id=1&action=edit, you do

    class Page(object):
        def GET(self):
            data = web.input()
            id = int(data.id)   # all the inputs are now strings. Cast it to int, to get integer.
            action = data.action
            ...

KeyError exception is thrown if key is not there in the URL parameters. Web.py makes it easier to handle that with default values to web.input().

    class Page(object):
        def GET(self):
            data = web.input(id=1, action='read')
            id, action = int(data.id), data.action
            ...

## POST

It works exactly the same way with POST method. If you have a form with name and password elements, you would do

    class Login(object):
        def POST(self):
            data = web.input()
            name, password = data.name, data.password
            ...

## Multiple inputs with same name

What if you have a URL which looks like /page?id=1&id=2&id=3 or you have a form with multiple selects? What would web.input().id give us? It simply swallows all but one value. But to let web.input() know that we’re expecting more values with the same name is simple. Just pass [] as the default argument for that name.

    class Page(object):
        def GET(self):
            data = web.input(id=[])
            ids = data.id         # now, `ids` is a list with all the `id`s.
            ...

## File uploads

Uploading files is easy with web.py. web.input() takes care of that too. Just make sure that the upload form has an attribute enctype=”multipart/form-data”. The input() gives you filename and value, which are the uploaded file name and the contents of it, respectively. To make things simpler, it also gives you file, a file-like object if you pass myfile={} where myfile is the name of the input element in your form.

    class Upload(object):
        def GET(self):
            return render.upload()

        def POST(self):
             data = web.input(myfile={})
             fp = data.myfile
             save(fp)   # fp.filename, fp.read() gives name and contents of the file
             ...

or

    class Upload(object):
        ...

        def POST(self):
             data = web.input() # notice that `myfile={}` is missing here.
             fp = data.myfile
             save(fp.filename, fp.value)
             ...