Errors with Python's mechanize module

Question

I'm using the mechanize module to execute some web queries from Python. I want my program to be error-resilient and handle all kinds of errors (wrong URLs, 403/404 responsese) gracefully. However, I can't find in mechanize's documentation the errors / exceptions it throws for various errors.

I just call it with:

    self.browser = mechanize.Browser()
    self.browser.addheaders = [('User-agent', browser_header)]

    self.browser.open(query_url)
    self.result_page = self.browser.response().read()

How can I know what errors / exceptions can be thrown here and handle them ?

Answer 1

$ perl -0777 -ne'print qq($1) if /__all__ = \[(.*?)\]/s' __init__.py | grep Error 

'BrowserStateError',
'ContentTooShortError',
'FormNotFoundError',
'GopherError',
'HTTPDefaultErrorHandler',
'HTTPError',
'HTTPErrorProcessor',
'LinkNotFoundError',
'LoadError',
'ParseError',
'RobotExclusionError',
'URLError',

Or:

>>> import mechanize
>>> filter(lambda s: "Error" in s, dir(mechanize))
['BrowserStateError', 'ContentTooShortError', 'FormNotFoundError', 'GopherError'
, 'HTTPDefaultErrorHandler', 'HTTPError', 'HTTPErrorProcessor', 'LinkNotFoundErr
or', 'LoadError', 'ParseError', 'RobotExclusionError', 'URLError']

Answer 2

While this has been posted a long time ago, I think there is still a need to answer the question correctly since it comes up in Google's search results for this very question.

As I write this, mechanize (version = (0, 1, 11, None, None)) in Python 265 raises urllib2.HTTPError and so the http status is available through catching this exception, eg:

import urllib2
try:
...  br.open("http://www.example.org/invalid-page")
... except urllib2.HTTPError, e:
...  print e.code
... 
404

Answer 3

I found this in their docs:

One final thing to note is that there are some catch-all bare except: statements in the module, which are there to handle unexpected bad input without crashing your program. If this happens, it's a bug in mechanize, so please mail me the warning text.

So I guess they don't raise any exceptions. You can also search the source code for Exception subclasses and see how they are used.