mechanize

Stateful programmatic web browsing in Python, after Andy Lester's Perl module WWW::Mechanize .

• mechanize.Browser is a subclass of mechanize.UserAgentBase, which is, in turn, a subclass of urllib2.OpenerDirector (in fact, of mechanize.OpenerDirector), so:
  • any URL can be opened, not just http:
  • mechanize.UserAgentBase offers easy dynamic configuration of user-agent features like protocol, cookie, redirection and robots.txt handling, without having to make a new OpenerDirector each time, e.g. by calling build_opener().
• Easy HTML form filling, using ClientForm interface.
• Convenient link parsing and following.
• Browser history (.back() and .reload() methods).
• The Referer HTTP header is added properly (optional).
• Automatic observance of robots.txt.
• Automatic handling of HTTP-Equiv and Refresh.

Examples

This documentation is in need of reorganisation and extension!

The two below are just to give the gist. There are also some actual working examples.

import re
from mechanize import Browser

br = Browser()
br.open("http://www.example.com/")
# follow second link with element text matching regular expression
response1 = br.follow_link(text_regex=r"cheese\s*shop", nr=1)
assert br.viewing_html()
print br.title()
print response1.geturl()
print response1.info()  # headers
print response1.read()  # body
response1.close()  # (shown for clarity; in fact Browser does this for you)

br.select_form(name="order")
# Browser passes through unknown attributes (including methods)
# to the selected HTMLForm (from ClientForm).
br["cheeses"] = ["mozzarella", "caerphilly"]  # (the method here is __setitem__)
response2 = br.submit()  # submit current form

# print currently selected form (don't call .submit() on this, use br.submit())
print br.form

response3 = br.back()  # back to cheese shop (same data as response1)
# the history mechanism returns cached response objects
# we can still use the response, even though we closed it:
response3.seek(0)
response3.read()
response4 = br.reload()  # fetches from server

for form in br.forms():
    print form
# .links() optionally accepts the keyword args of .follow_/.find_link()
for link in br.links(url_regex="python.org"):
    print link
    br.follow_link(link)  # takes EITHER Link instance OR keyword args
    br.back()

You may control the browser's policy by using the methods of mechanize.Browser's base class, mechanize.UserAgent. For example:

br = Browser()
# Explicitly configure proxies (Browser will attempt to set good defaults).
# Note the userinfo ("joe:password@") and port number (":3128") are optional.
br.set_proxies({"http": "joe:password@myproxy.example.com:3128",
                "ftp": "proxy.example.com",
                })
# Add HTTP Basic/Digest auth username and password for HTTP proxy access.
# (equivalent to using "joe:password@..." form above)
br.add_proxy_password("joe", "password")
# Add HTTP Basic/Digest auth username and password for website access.
br.add_password("http://example.com/protected/", "joe", "password")
# Don't handle HTTP-EQUIV headers (HTTP headers embedded in HTML).
br.set_handle_equiv(False)
# Ignore robots.txt.  Do not do this without thought and consideration.
br.set_handle_robots(False)
# Don't add Referer (sic) header
br.set_handle_referer(False)
# Don't handle Refresh redirections
br.set_handle_refresh(False)
# Don't handle cookies
br.set_cookiejar()
# Supply your own mechanize.CookieJar (NOTE: cookie handling is ON by
# default: no need to do this unless you have some reason to use a
# particular cookiejar)
br.set_cookiejar(cj)
# Log information about HTTP redirects and Refreshes.
br.set_debug_redirects(True)
# Log HTTP response bodies (ie. the HTML, most of the time).
br.set_debug_responses(True)
# Print HTTP headers.
br.set_debug_http(True)

# To make sure you're seeing all debug output:
logger = logging.getLogger("mechanize")
logger.addHandler(logging.StreamHandler(sys.stdout))
logger.setLevel(logging.INFO)

# Sometimes it's useful to process bad headers or bad HTML:
response = br.response()  # this is a copy of response
headers = response.info()  # currently, this is a mimetools.Message
headers["Content-type"] = "text/html; charset=utf-8"
response.set_data(response.get_data().replace("<!---", "<!--"))
br.set_response(response)

mechanize exports the complete interface of urllib2:

import mechanize
response = mechanize.urlopen("http://www.example.com/")
print response.read()

so anything you would normally import from urllib2 can (and should, by preference, to insulate you from future changes) be imported from mechanize instead. In many cases if you import an object from mechanize it will be the very same object you would get if you imported from urllib2. In many other cases, though, the implementation comes from mechanize, either because bug fixes have been applied or the functionality of urllib2 has been extended in some way.

UserAgent vs UserAgentBase

mechanize.UserAgent is a trivial subclass of mechanize.UserAgentBase, adding just one method, .set_seekable_responses() (see the documentation on seekable responses).

The reason for the extra class is that mechanize.Browser depends on seekable response objects (because response objects are used to implement the browser history).

Compatibility

These notes explain the relationship between mechanize, ClientCookie, cookielib and urllib2, and which to use when. If you're just using mechanize, and not any of those other libraries, you can ignore this section.

1. mechanize works with Python 2.4, Python 2.5, and Python 2.6.
2. ClientCookie is no longer maintained as a separate package. The code is now part of mechanize, and its interface is now exported through module mechanize (since mechanize 0.1.0). Old code can simply be changed to import mechanize as ClientCookie and should continue to work.
3. The cookie handling parts of mechanize are in Python 2.4 standard library as module cookielib and extensions to module urllib2.

IMPORTANT: The following are the ONLY cases where mechanize and urllib2 code are intended to work together. For all other code, use mechanize exclusively: do NOT mix use of mechanize and urllib2!

1. Handler classes that are missing from 2.4's urllib2 (e.g. HTTPRefreshProcessor, HTTPEquivProcessor, HTTPRobotRulesProcessor) may be used with the urllib2 of Python 2.4 or newer. There are not currently any functional tests for this in mechanize, however, so this feature may be broken.
2. If you want to use mechanize.RefreshProcessor with Python >= 2.4's urllib2, you must also use mechanize.HTTPRedirectHandler.
3. mechanize.HTTPRefererProcessor requires special support from mechanize.Browser, so cannot be used with vanilla urllib2.
4. mechanize.HTTPRequestUpgradeProcessor and mechanize.ResponseUpgradeProcessor are not useful outside of mechanize.
5. Request and response objects from code based on urllib2 work with mechanize, and vice-versa.
6. The classes and functions exported by mechanize in its public interface that come straight from urllib2 (e.g. FTPHandler, at the time of writing) do work with mechanize (duh ;-). Exactly which of these classes and functions come straight from urllib2 without extension or modification will change over time, though, so don't rely on it; instead, just import everything you need from mechanize, never from urllib2. The exception is usage as described in the first item in this list, which is explicitly OK (though not well tested ATM), subject to the other restrictions in the list above .

Documentation

Full documentation is in the docstrings.

The documentation in the web pages is in need of reorganisation at the moment, after the merge of ClientCookie into mechanize.

Credits

Thanks to all the too-numerous-to-list people who reported bugs and provided patches. Also thanks to Ian Bicking, for persuading me that a UserAgent class would be useful, and to Ronald Tschalar for advice on Netscape cookies.

A lot of credit must go to Gisle Aas, who wrote libwww-perl, from which large parts of mechanize originally derived, and Andy Lester for the original, WWW::Mechanize . Finally, thanks to the (coincidentally-named) Johnny Lee for the MSIE CookieJar Perl code from which mechanize's support for that is derived.

To do

Contributions welcome!

The documentation to-do list has moved to the new "docs-in-progress" directory in SVN.

This is very roughly in order of priority

• Test .any_response() two handlers case: ordering.
• Test referer bugs (frags and don't add in redirect unless orig req had Referer)
• Remove use of urlparse from _auth.py.
• Proper XHTML support!
• Fix BeautifulSoup support to use a single BeautifulSoup instance per page.
• Test BeautifulSoup support better / fix encoding issue.
• Support BeautifulSoup 3.
• Add another History implementation or two and finalise interface.
• History cache expiration.
• Investigate possible leak further (see Balazs Ree's list posting).
• Make EncodingFinder public, I guess (but probably improve it first). (For example: support Mark Pilgrim's universal encoding detector?)
• Add two-way links between BeautifulSoup & ClientForm object models.
• In 0.2: switch to Python unicode strings everywhere appropriate (HTTP level should still use byte strings, of course).
• clean_url(): test browser behaviour. I think this is correct...
• Use a nicer RFC 3986 join / split / unsplit implementation.
• Figure out the Right Thing (if such a thing exists) for %-encoding.
• How do IRIs fit into the world?
• IDNA -- must read about security stuff first.
• Unicode support in general.
• Provide per-connection access to timeouts.
• Keep-alive / connection caching.
• Pipelining??
• Content negotiation.
• gzip transfer encoding (there's already a handler for this in mechanize, but it's poorly implemented ATM).
• proxy.pac parsing (I don't think this needs JS interpretation)
• Topological sort for handlers, instead of .handler_order attribute. Ordering and other dependencies (where unavoidable) should be defined separate from handlers themselves. Add new build_opener and deprecate the old one? Actually, _useragent is probably not far off what I'd have in mind (would just need a method or two and a base class adding I think), and it's not a high priority since I guess most people will just use the UserAgent and Browser classes.

Getting mechanize

You can install the old-fashioned way, or using EasyInstall. I recommend the latter even though EasyInstall is still in alpha, because it will automatically ensure you have the necessary dependencies, downloading if necessary.

Subversion (SVN) access is also available.

Since EasyInstall is new, I include some instructions below, but mechanize follows standard EasyInstall / setuptools conventions, so you should refer to the EasyInstall and setuptools documentation if you need more detailed or up-to-date instructions.

EasyInstall / setuptools

The benefit of EasyInstall and the new setuptools-supporting setup.py is that they grab all dependencies for you. Also, using EasyInstall is a one-liner for the common case, to be compared with the usual download-unpack-install cycle with setup.py.

Using EasyInstall to download and install mechanize

1. Install easy_install
2. easy_install mechanize

If you're on a Unix-like OS, you may need root permissions for that last step (or see the EasyInstall documentation for other installation options).

If you already have mechanize installed as a Python Egg (as you do if you installed using EasyInstall, or using setup.py install from mechanize 0.0.10a or newer), you can upgrade to the latest version using:

easy_install --upgrade mechanize

You may want to read up on the -m option to easy_install, which lets you install multiple versions of a package.

Using EasyInstall to download and install the latest in-development (SVN HEAD) version of mechanize

easy_install "mechanize==dev"

Note that that will not necessarily grab the SVN versions of dependencies, such as ClientForm: It will use SVN to fetch dependencies if and only if the SVN HEAD version of mechanize declares itself to depend on the SVN versions of those dependencies; even then, those declared dependencies won't necessarily be on SVN HEAD, but rather a particular revision. If you want SVN HEAD for a dependency project, you should ask for it explicitly by running easy_install "projectname=dev" for that project.

Note also that you can still carry on using a plain old SVN checkout as usual if you like.

Using setup.py from a .tar.gz, .zip or an SVN checkout to download and install mechanize

setup.py should correctly resolve and download dependencies:

python setup.py install

Or, to get access to the same options that easy_install accepts, use the easy_install distutils command instead of install (see python setup.py --help easy_install)

python setup.py easy_install mechanize

Download

All documentation (including this web page) is included in the distribution.

This is a stable release.

Development release.

• mechanize-0.1.11.tar.gz
• mechanize-0.1.11.zip
• Change Log (included in distribution)
• Older versions.

For old-style installation instructions, see the INSTALL file included in the distribution. Better, use EasyInstall.

Subversion

The Subversion (SVN) trunk is http://codespeak.net/svn/wwwsearch/mechanize/trunk, so to check out the source:

svn co http://codespeak.net/svn/wwwsearch/mechanize/trunk mechanize

Tests and examples

Examples

The examples directory in the source packages contains a couple of silly, but working, scripts to demonstrate basic use of the module. Note that it's in the nature of web scraping for such scripts to break, so don't be too suprised if that happens – do let me know, though!

It's worth knowing also that the examples on the ClientForm web page are useful for mechanize users, and are now real run-able scripts rather than just documentation.

Functional tests

To run the functional tests (which do access the network), run the following command:

python functional_tests.py

Unit tests

Note that ClientForm (a dependency of mechanize) has its own unit tests, which must be run separately.

To run the unit tests (none of which access the network), run the following command:

python test.py

This runs the tests against the source files extracted from the package. For help on command line options:

python test.py --help

See also

There are several wrappers around mechanize designed for functional testing of web applications:

• zope.testbrowser (or ZopeTestBrowser, the standalone version).
• twill.

Richard Jones' webunit (this is not the same as Steven Purcell's code of the same name). webunit and mechanize are quite similar. On the minus side, webunit is missing things like browser history, high-level forms and links handling, thorough cookie handling, refresh redirection, adding of the Referer header, observance of robots.txt and easy extensibility. On the plus side, webunit has a bunch of utility functions bound up in its WebFetcher class, which look useful for writing tests (though they'd be easy to duplicate using mechanize). In general, webunit has more of a frameworky emphasis, with aims limited to writing tests, where mechanize and the modules it depends on try hard to be general-purpose libraries.

There are many related links in the General FAQ page, too.

FAQs - pre install

• Which version of Python do I need?

  Python 2.4, 2.5 or 2.6.

• What else do I need?

  mechanize depends on ClientForm.

• Does mechanize depend on BeautifulSoup? No. mechanize offers a few (still rather experimental) classes that make use of BeautifulSoup, but these classes are not required to use mechanize. mechanize bundles BeautifulSoup version 2, so that module is no longer required. A future version of mechanize will support BeautifulSoup version 3, at which point mechanize will likely no longer bundle the module.

  The versions of those required modules are listed in the setup.py for mechanize (included with the download). The dependencies are automatically fetched by EasyInstall (or by downloading a mechanize source package and running python setup.py install). If you like you can fetch and install them manually, instead – see the INSTALL.txt file (included with the distribution).

• Which license?

  mechanize is dual-licensed: you may pick either the BSD license, or the ZPL 2.1 (both are included in the distribution).

FAQs - usage

• I'm not getting the HTML page I expected to see.
  • Debugging tips
  • More tips
• I'm sure this page is HTML, why does mechanize.Browser think otherwise?

  b = mechanize.Browser(
      # mechanize's XHTML support needs work, so is currently switched off.  If
      # we want to get our work done, we have to turn it on by supplying a
      # mechanize.Factory (with XHTML support turned on):
      factory=mechanize.DefaultFactory(i_want_broken_xhtml_support=True)
      )

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

John J. Lee, December 2008.

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