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mechanize — Forms

This documentation is in need of reorganisation!

This page is the old ClientForm documentation. ClientForm is now part of mechanize, but the documentation hasn’t been fully updated to reflect that: what’s here is correct, but not well-integrated with the rest of the documentation. This page deals with HTML form handling: parsing HTML forms, filling them in and returning the completed forms to the server. See the front page for how to obtain form objects from a mechanize.Browser.

Simple working example (examples/forms/ in the source distribution):

import sys

from mechanize import ParseResponse, urlopen, urljoin

if len(sys.argv) == 1:
uri = ""
uri = sys.argv[1]

response = urlopen(urljoin(uri, "mechanize/example.html"))
forms = ParseResponse(response, backwards_compat=False)
form = forms[0]
print form
form["comments"] = "Thanks, Gisle"

# returns a mechanize.Request object
# (see if you want to use only the forms support, and
# not the rest of mechanize)
print urlopen(

A more complicated working example (from examples/forms/ in the source distribution):

import sys

import mechanize

if len(sys.argv) == 1:
uri = ""
uri = sys.argv[1]

request = mechanize.Request(mechanize.urljoin(uri, "mechanize/example.html"))
response = mechanize.urlopen(request)
forms = mechanize.ParseResponse(response, backwards_compat=False)
## f = open("example.html")
## forms = mechanize.ParseFile(f, "",
## backwards_compat=False)
## f.close()
form = forms[0]
print form # very useful!

# A 'control' is a graphical HTML form widget: a text entry box, a
# dropdown 'select' list, a checkbox, etc.

# Indexing allows setting and retrieval of control values
original_text = form["comments"] # a string, NOT a Control instance
form["comments"] = "Blah."

# Controls that represent lists (checkbox, select and radio lists) are
# ListControl instances. Their values are sequences of list item names.
# They come in two flavours: single- and multiple-selection:
form["favorite_cheese"] = ["brie"] # single
form["cheeses"] = ["parmesan", "leicester", "cheddar"] # multi
# equivalent, but more flexible:
form.set_value(["parmesan", "leicester", "cheddar"], name="cheeses")

# Add files to FILE controls with .add_file(). Only call this multiple
# times if the server is expecting multiple files.
# add a file, default value for MIME type, no filename sent to server
# add a second file, explicitly giving MIME type, and telling the server
# what the filename is
form.add_file(open("data.txt"), "text/plain", "data.txt")

# All Controls may be disabled (equivalent of greyed-out in browser)...
control = form.find_control("comments")
print control.disabled
# ...or readonly
print control.readonly
# readonly and disabled attributes can be assigned to
control.disabled = False
# convenience method, used here to make all controls writable (unless
# they're disabled):

# A couple of notes about list controls and HTML:

# 1. List controls correspond to either a single SELECT element, or
# multiple INPUT elements. Items correspond to either OPTION or INPUT
# elements. For example, this is a SELECT control, named "control1":

# <select name="control1">
# <option>foo</option>
# <option value="1">bar</option>
# </select>

# and this is a CHECKBOX control, named "control2":

# <input type="checkbox" name="control2" value="foo" id="cbe1">
# <input type="checkbox" name="control2" value="bar" id="cbe2">

# You know the latter is a single control because all the name attributes
# are the same.

# 2. Item names are the strings that go to make up the value that should
# be returned to the server. These strings come from various different
# pieces of text in the HTML. The HTML standard and the mechanize
# docstrings explain in detail, but playing around with an HTML file,
# ParseFile() and 'print form' is very useful to understand this!

# You can get the Control instances from inside the form...
control = form.find_control("cheeses", type="select")
print, control.value, control.type
control.value = ["mascarpone", "curd"]
# ...and the Item instances from inside the Control
item = control.get("curd")
print, item.selected,, item.attrs
item.selected = False

# Controls may be referred to by label:
# find control with label that has a *substring* "Cheeses"
# (e.g., a label "Please select a cheese" would match).
control = form.find_control(label="select a cheese")

# You can explicitly say that you're referring to a ListControl:
# set value of "cheeses" ListControl
form.set_value(["gouda"], name="cheeses", kind="list")
# equivalent:
form.find_control(name="cheeses", kind="list").value = ["gouda"]
# the first example is also almost equivalent to the following (but
# insists that the control be a ListControl -- so it will skip any
# non-list controls that come before the control we want)
form["cheeses"] = ["gouda"]
# The kind argument can also take values "multilist", "singlelist", "text",
# "clickable" and "file":
# find first control that will accept text, and scribble in it
form.set_value("rhubarb rhubarb", kind="text", nr=0)
# find, and set the value of, the first single-selection list control
form.set_value(["spam"], kind="singlelist", nr=0)

# You can find controls with a general predicate function:
def control_has_caerphilly(control):
for item in control.items:
if == "caerphilly": return True
form.find_control(kind="list", predicate=control_has_caerphilly)

# HTMLForm.controls is a list of all controls in the form
for control in form.controls:
if control.value == "inquisition": sys.exit()

# Control.items is a list of all Item instances in the control
for item in form.find_control("cheeses").items:

# To remove items from a list control, remove it from .items:
cheeses = form.find_control("cheeses")
curd = cheeses.get("curd")
del cheeses.items[cheeses.items.index(curd)]
# To add items to a list container, instantiate an Item with its control
# and attributes:
# Note that you are responsible for getting the attributes correct here,
# and these are not quite identical to the original HTML, due to
# defaulting rules and a few special attributes (e.g. Items that represent
# OPTIONs have a special "contents" key in their .attrs dict). In future
# there will be an explicitly supported way of using the parsing logic to
# add items and controls from HTML strings without knowing these details.
mechanize.Item(cheeses, {"contents": "mascarpone",
"value": "mascarpone"})

# You can specify list items by label using set/get_value_by_label() and
# the label argument of the .get() method. Sometimes labels are easier to
# maintain than names, sometimes the other way around.
form.set_value_by_label(["Mozzarella", "Caerphilly"], "cheeses")

# Which items are present, selected, and successful?
# is the "parmesan" item of the "cheeses" control successful (selected
# and not disabled)?
print "parmesan" in form["cheeses"]
# is the "parmesan" item of the "cheeses" control selected?
print "parmesan" in [ for item in form.find_control("cheeses").items if item.selected]
# does cheeses control have a "caerphilly" item?
print "caerphilly" in [ for item in form.find_control("cheeses").items]

# Sometimes one wants to set or clear individual items in a list, rather
# than setting the whole .value:
# select the item named "gorgonzola" in the first control named "cheeses"
form.find_control("cheeses").get("gorgonzola").selected = True
# You can be more specific:
# deselect "edam" in third CHECKBOX control
form.find_control(type="checkbox", nr=2).get("edam").selected = False
# deselect item labelled "Mozzarella" in control with id "chz"
form.find_control(id="chz").get(label="Mozzarella").selected = False

# Often, a single checkbox (a CHECKBOX control with a single item) is
# present. In that case, the name of the single item isn't of much
# interest, so it's a good idea to check and uncheck the box without
# using the item name:
form.find_control("smelly").items[0].selected = True # check
form.find_control("smelly").items[0].selected = False # uncheck

# Items may be disabled (selecting or de-selecting a disabled item is
# not allowed):
control = form.find_control("cheeses")
print control.get("emmenthal").disabled
control.get("emmenthal").disabled = True
# enable all items in control

request2 = # mechanize.Request object
response2 = mechanize.urlopen(request2)
except mechanize.HTTPError, response2:

print response2.geturl()
# headers
for name, value in
if name != "date":
print "%s: %s" % (name.title(), value)
print # body

All of the standard control types are supported: TEXT, PASSWORD, HIDDEN, TEXTAREA, ISINDEX, RESET, BUTTON (INPUT TYPE=BUTTON and the various BUTTON types), SUBMIT, IMAGE, RADIO, CHECKBOX, SELECT/OPTION and FILE (for file upload). Both standard form encodings (application/x-www-form-urlencoded and multipart/form-data) are supported.

The module is designed for testing and automation of web interfaces, not for implementing interactive user agents.

Security note: Remember that any passwords you store in HTMLForm instances will be saved to disk in the clear if, for example, you pickle them.


There are two parsers.

TODO: more!

See also the FAQ entries on XHTML and parsing bad HTML.

Backwards-compatibility mode

mechanize (and ClientForm 0.2) includes three minor backwards-incompatible interface changes from ClientForm version 0.1.

To make upgrading from ClientForm 0.1 easier, and to allow me to stop supporting version ClientForm 0.1 sooner, there is support for operating in a backwards-compatible mode, under which code written for ClientForm 0.1 should work without modification. This is done on a per-HTMLForm basis via the .backwards_compat attribute, but for convenience the ParseResponse() and ParseFile() factory functions accept backwards_compat arguments. These backwards-compatibility features will be removed soon. The default is to operate in backwards-compatible mode. To run with backwards compatible mode turned OFF (strongly recommended):

from mechanize import ParseResponse, urlopen
forms = ParseResponse(urlopen(""), backwards_compat=False)
# ...

The backwards-incompatible changes are:

  • Ambiguous specification of controls or items now results in AmbiguityError. If you want the old behaviour, explicitly pass nr=0 to indicate you want the first matching control or item.

  • Item label matching is now done by substring, not by strict string-equality (but note leading and trailing space is always stripped). (Control label matching is always done by substring.)

  • Handling of disabled list items has changed. First, note that handling of disabled list items in ClientForm 0.1 (and in ClientForm 0.2’s backwards-compatibility mode!) is buggy: disabled items are successful (ie. disabled item names are sent back to the server). As a result, there was no distinction to be made between successful items and selected items. In ClientForm 0.2, the bug is fixed, so this is no longer the case, and it is important to note that list controls’ .value attribute contains only the successful item names; items that are selected but not successful (because disabled) are not included in .value. Second, disabled list items may no longer be deselected: AttributeError is raised in ClientForm 0.2, whereas deselection was allowed in ClientForm 0.1. The bug in ClientForm 0.1 and in ClientForm 0.2’s backwards-compatibility mode will not be fixed, to preserve compatibility and to encourage people to upgrade to the new ClientForm 0.2 backwards_compat=False behaviour.

I prefer questions and comments to be sent to the mailing list rather than direct to me.

John J. Lee, April 2010.