Nov. 06, 2012

Python Mechanize Cheat Sheet

Mechanize

A very useful python module for navigating through web forms is Mechanize. 

In a previous post I wrote about "Browsing in Python with Mechanize". 

Today I found this excellent cheat sheet on scraperwiki that I would like to
share. 

Create a browser object

Create a browser object and give it some optional settings.
import mechanize
br = mechanize.Browser()
br.set_all_readonly(False)    # allow everything to be written to
br.set_handle_robots(False)   # ignore robots
br.set_handle_refresh(False)  # can sometimes hang without this
br.addheaders =   	      	# [('User-agent', 'Firefox')]

Open a webpage

Open a webpage and inspect its contents
response = br.open(url)
print response.read()      # the text of the page
response1 = br.response()  # get the response again
print response1.read()     # can apply lxml.html.fromstring()

Using forms

List the forms that are in the page
for form in br.forms():
    print "Form name:", form.name
    print form
To go on the mechanize browser object must have a form selected
br.select_form("form1")         # works when form has a name
br.form = list(br.forms())[0]  # use when form is unnamed

Using Controls

Iterate through the controls in the form.
for control in br.form.controls:
    print control
    print "type=%s, name=%s value=%s" % (control.type, control.name, br[control.name])
Controls can be found by name
control = br.form.find_control("controlname")
Having a select control tells you what values can be selected
if control.type == "select":  # means it's class ClientForm.SelectControl
    for item in control.items:
    print " name=%s values=%s" % (item.name, str([label.text  for label in item.get_labels()]))
Because 'Select' type controls can have multiple selections, they must be set
with a list, even if it is one element.
print control.value
print control  # selected value is starred
control.value = ["ItemName"]
print control
br[control.name] = ["ItemName"]  # equivalent and more normal
Text controls can be set as a string
if control.type == "text":  # means it's class ClientForm.TextControl
    control.value = "stuff here"
br["controlname"] = "stuff here"  # equivalent
Controls can be set to readonly and disabled.
control.readonly = False
control.disabled = True
OR disable all of them like so
for control in br.form.controls:
   if control.type == "submit":
       control.disabled = True

Submit the form

When your form is complete you can submit
 
response = br.submit()
print response.read()
br.back()   # go back

Finding Links

Following links in mechanize is a hassle because you need the have the link
object.

Sometimes it is easier to get them all and find the link you want from the text.
for link in br.links():
    print link.text, link.url
Follow link and click links is the same as submit and click
request = br.click_link(link)
response = br.follow_link(link)
print response.geturl()
I hope that you got more understanding of the Mechanize module in Python.


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