Overview

This is a drop-in replacement for cgi.FieldStorage which has been removed from Python as of v3.13

It handles GET, HEAD, POST, and POST with multipart/form-data

It has been tested sufficiently for my own applications. I make no guarantees that it will work in your environment. If you find and fix any bugs, feel free to submit a pull request.

Unlike the original cgi.FieldStorage class, this variant uses urllib.parse.parse_qsl() and email.message to do the heavy lifting. This implementation merely assembles the results into a form compatible with the original API.

To use:

from fieldstorage import FieldStorage

:

form = FieldStorage()	# This reads the form data

source = form.getfirst('source')
style = form.getfirst('style')

etc.

API

Constructor

FieldStorage(fp=None, headers=None, outerboundary=b'',
             environ=os.environ, keep_blank_values=0, strict_parsing=0,
             limit=None, encoding='utf-8', errors='replace',
             max_num_fields=None, separator='&')

All arguments are optional, and usually this class can be used successfully without specifying any.

FieldStorage objects are dictionary-like objects, but that's not the best way to access them.

Note that since HTML forms allow duplicate item names, each key in the FieldStorage object may have multiple values. Depending on how you access the item, you may get a single value or a list of values.

• fp — file-like object to be used for input (POST). Default is stdin.
• headers — initial value for headers
• outerboundary — ignored by this implementation
• environ — environment variables. Default is os.environ
• keep_blank_values — passed to urllib.parse.parse_qs()
• strict_parsing — passed to urllib.parse.parse_qs()
• limit — ignored by this implementation
• encoding — passed to urllib.parse.parse_qs()
• errors — passed to urllib.parse.parse_qs()
• max_num_fields — passed to urllib.parse.parse_qs()
• separator — passed to urllib.parse.parse_qs()

Properties

These are the properties when the FieldStorage object is used to hold a file.

• name: name of the form field
• value: the entire content of the item as bytes (file) or a string (everything else)
• file: a file-like object from which the data can be read *
• filename: name of file for file inputs, else None
• type: mime-type as a string
• type_options: a dict containing extra informaton from the type
• headers: the HTTP headers for this form part
• disposition: the Content-Disposition header

* At present, there's little reason to use the file property, as the entire file is kept in memory anyway. Just use the value property. (This was true for the original cgi.FieldStorage as well.) This is only useful if there's something in your application that was expecting a file.

Methods

• [key] — dictionary-like indexing. May return a single MiniFieldStorage or FileFieldStorage object, or a list of such objects if the key had multiple values.
• getvalue(key) — Returns the underlying values rather than MiniFieldStorage objects. Returns a singleton or a list depending on whether there are multiple values for this key.
• getfirst(key) — Returns the first value rather than a list
• getlistt(key) — Returns a list of values, even if there's only one

Bugs

The repr() function does not return a string that will correctly create a new FieldStorage.

The original seemed to append extra newlines to some header values. This version does not do that.

Notes

The original FieldStorage stored all of its data in a list. This version uses a dict. Except for files, values are stored directly in the dict rather than in nested MiniFieldStorage objects. This causes subtle changes in how repr() and the value property behave.