import cStringIO as StringIO
import os
class ReadCallbackStream(object):
"""Wraps a file-like object in another, but also calls a user
callback with the number of bytes read whenever its `read()` method
is called. Used for tracking upload progress, for example for a
progress bar in a UI application. Idea taken from ActiveState Code Recipe:
http://code.activestate.com/recipes/578669-wrap-a-string-in-a-file-like-object-that-calls-a-u/
"""
def __init__(self, file_like, callback):
self.file_like = file_like
self._callback = callback
def __len__(self):
raise NotImplementedError()
def read(self, *args):
chunk = self.file_like.read(*args)
if len(chunk) > 0:
self._callback(len(chunk))
return chunk
class ReadCallbackString(ReadCallbackStream):
def __init__(self, data, callback):
super(ReadCallbackString, self).__init__(StringIO.StringIO(data), callback)
self._len = len(data)
def __len__(self):
return self._len
class ReadCallbackFile(ReadCallbackStream):
def __init__(self, filename, callback):
super(ReadCallbackFile, self).__init__(open(filename), callback)
def __len__(self):
curpos = self.file_like.tell()
self.file_like.seek(0, os.SEEK_END)
file_length = self.file_like.tell() - curpos
self.file_like.seek(curpos, os.SEEK_SET)
return file_length
if __name__ == '__main__':
import json
import urllib2
def callback(num_bytes_read):
print 'callback:', num_bytes_read, 'bytes read'
data = 'x' * 20000
stream = ReadCallbackString(data, callback)
request = urllib2.Request('http://httpbin.org/post', stream)
f = urllib2.urlopen(request)
response = json.loads(f.read())
print 'httpbin.org said we POSTed', len(response['data']), 'bytes'
# create a real file and repeat process
print
filename = 'testfile'
with open(filename, 'w') as testfile:
testfile.write(data)
stream = ReadCallbackFile(filename, callback)
request = urllib2.Request('http://httpbin.org/post', stream)
f = urllib2.urlopen(request)
response = json.loads(f.read())
print 'httpbin.org said we POSTed', len(response['data']), 'bytes'
