4.6.1 FieldStorage class
Description: FieldStorage class
Keywords: modpython

##
4.6.1 FieldStorage class

Access to form data is provided via the `FieldStorage` class. This class is similar to the standard library module `cgi` `FieldStorage`.

class `FieldStorage`( | req[, keep_blank_values, strict_parsing])

  This class provides uniform access to HTML form data submitted by the client. req is an instance of the mod_python request object.

  The optional argument keep_blank_values is a flag indicating whether blank values in URL encoded form data should be treated as blank strings. The default is false, which means that blank values are ignored as if they were not included.

  The optional argument strict_parsing is not yet implemented.

  During initialization, `FieldStorage` class reads all of the data provided by the client. Since all data provided by the client is consumed at this point, there should be no more than one `FieldStorage` class instantiated per single request, nor should you make any attempts to read client data before or after instantiating a `FieldStorage`.

  The data read from the client is then parsed into separate fields and packaged in `Field` objects, one per field. For HTML form inputs of type `file`, a temporary file is created that can later be accessed via the `file` attribute of a `Field` object.

  The `FieldStorage` class has a mapping object interface, i.e. it can be treated like a dictionary. When used as a mapping, the keys are form input names, and the returned dictionary value can be:

  - An instance of `StringField`, containing the form input value. This is only when there is a single value corresponding to the input name. `StringField` is a subclass of `str` which provides the additional `value` attribute for compatibility with standard library `cgi` module.
  - An instance of a `Field` class, if the input is a file upload.
  - A list of `StringField` and/or `Field` objects. This is when multiple values exist, such as for a `<select>` HTML form element.

  Note: Unlike the standard library `cgi` module `FieldStorage` class, a `Field` object is returned only when it is a file upload. In all other cases the return is an instance of `StringField`. This means that you do not need to use the `.value` attribute to access values of fields in most cases.

  In addition to standard mapping object methods, `FieldStorage` objects have the following attributes:

  `list`
    This is a list of `Field` objects, one for each input. Multiple inputs with the same name will have multiple elements in this list.

  `FieldStorage` methods:

  `getfirst`( | name[, default])

    Always returns only one value associated with form field name. If no such form field or value exists then the method returns the value specified by the optional parameter default. This parameter defaults to `None` if not specified.

  `getlist`( | name)

    This method always returns a list of values associated with form field name. The method returns an empty list if no such form field or value exists for name. It returns a list consisting of one item if only one such value exists.