Python - POST HTTP multipart form (Using standard urllib libraries)

The Python script in this example utilises standard Python libraries to POST a form with content type multipart/form-data over HTTP (or quite simply, a multipart form).

The content type "multipart/form-data" should be used for submitting forms that contain files, non-ASCII data, and binary data.

I won't delve deep into the details on multipart forms, but if you would like a good explanation, read the official W3C document. One thing if doesn't mention on there, is that the boundary can be between 1 and 70 characters long, consisting of alphanumeric, and the punctuation you see in the list. Spaces are allowed except at the end.

Code Snippet

1.     import itertools
2.     import mimetools
3.     import mimetypes
4.     from cStringIO import StringIO
5.     import urllib
6.     import urllib2
7.      
8.     class MultiPartForm(object):
9.         """Accumulate the data to be used when posting a form."""
10.      
11.         def __init__(self):
12.             self.form_fields = []
13.             self.files = []
14.            
15.             # Generate unique boundary string with the format: hostipaddr.uid.pid.timestamp.random
16.             self.boundary = mimetools.choose_boundary()
17.             return
18.        
19.         def get_content_type(self):
20.             return 'multipart/form-data; boundary=%s' % self.boundary
21.      
22.         def add_field(self, name, value):
23.             """Add a simple field to the form data."""
24.             self.form_fields.append((name, value))
25.             return
26.      
27.         def add_file(self, fieldname, filename, fileHandle, mimetype=None):
28.             """Add a file to be uploaded."""
29.             body = fileHandle.read()
30.             if mimetype is None:
31.                 mimetype = mimetypes.guess_type(filename)[0] or 'application/octet-stream'
32.             self.files.append((fieldname, filename, mimetype, body))
33.             return
34.        
35.         def __str__(self):
36.             """Return a string representing the form data, including attached files."""
37.             # Build a list of lists, each containing "lines" of the
38.             # request.  Each part is separated by a boundary string.
39.             # Once the list is built, return a string where each
40.             # line is separated by '\r\n'.  
41.             parts = []
42.             part_boundary = '--' + self.boundary
43.            
44.             # Add the form fields
45.             parts.extend(
46.                 [ part_boundary,
47.                   'Content-Disposition: form-data; name="%s"' % name,
48.                   '',
49.                   value,
50.                 ]
51.                 for name, value in self.form_fields
52.                 )
53.            
54.             # Add the files to upload
55.             parts.extend(
56.                 [ part_boundary,
57.                   'Content-Disposition: file; name="%s"; filename="%s"' % \
58.                      (field_name, filename),
59.                   'Content-Type: %s' % content_type,
60.                   '',
61.                   body,
62.                 ]
63.                 for field_name, filename, content_type, body in self.files
64.                 )
65.            
66.             # Flatten the list and add closing boundary marker,
67.             # then return CR+LF separated data
68.             flattened = list(itertools.chain(*parts))
69.             flattened.append('--' + self.boundary + '--')
70.             flattened.append('')
71.             return '\r\n'.join(flattened)
72.      
73.      
74.      
75.      
76.      
77.     if __name__ == '__main__':
78.      
79.         # Create the form with simple fields
80.         form = MultiPartForm()
81.        
82.        
83.         """
84.            Either specify a source, file or a url...
85.            The system will take the first one respectively if all three have content.
86.            This example uses a dummy file called test.sql, with a string of content.
87.       """
88.        
89.         # No source specified
90.         form.add_field('source', '')
91.        
92.         # REAL FILE EXAMPLE
93.         # fileHandle = open ('test.sql', 'r')
94.         # form.add_file('file', 'test.sql', fileHandle)
95.         # fileHandle.close()
96.        
97.         # Use dummy file
98.         form.add_file('file', 'test.sql', fileHandle=StringIO('FILE CONTENTS'))
99.        
100.         # No URL specified
101.         form.add_field('url', '')
102.        
103.        
104.        
105.         # Add remaining required parameters
106.         form.add_field('language', 'php')
107.         form.add_field('line_numbers', '2')
108.         form.add_field('word_wrap', 'on')
109.         form.add_field('tab_width', '8')
110.         form.add_field('highlight_keywords', 'on')
111.         form.add_field('default_color', '0000bb')
112.         form.add_field('keyword_colors[1]', 'DEFAULT')
113.         form.add_field('keyword_colors[2]', 'DEFAULT')
114.         form.add_field('keyword_colors[3]', 'DEFAULT')
115.         form.add_field('keyword_colors[4]', 'DEFAULT')
116.         form.add_field('comments_color', 'DEFAULT')
117.         form.add_field('escaped_chars_color', 'DEFAULT')
118.         form.add_field('brackets_color', 'DEFAULT')
119.         form.add_field('strings_color', 'DEFAULT')
120.         form.add_field('numbers_color', 'DEFAULT')
121.         form.add_field('methods_color', 'DEFAULT')
122.      
123.         # Build the request
124.         request = urllib2.Request('http://qbnz.com/highlighter/php_highlighter.php')
125.        
126.         # Hi i'm FireFox 5
127.         request.add_header('User-agent', 'Mozilla/5.0 (Windows; U; Windows NT 5.1; it; rv:1.8.1.11) Gecko/20071127 Firefox/2.0.0.11')
128.        
129.         # We are required to specify the content type and length...
130.         body = str(form)
131.         request.add_header('Content-type', form.get_content_type())
132.         request.add_header('Content-length', len(body))
133.         request.add_data(body)
134.      
135.             # Take a look at what we are sending... useful to match up against the required request
136.         print
137.         print 'OUTGOING DATA:'
138.         print request.get_data()
139.      
140.             # View servers response
141.         print
142.         print 'SERVER RESPONSE:'
143.         print urllib2.urlopen(request).read()

End of Code Snippet