David Wolever David Wolever - 11 months ago 61
Python Question

Python: Convert an iterable to a stream?

If I've got an iterable containing strings, is there a simple way to turn it into a stream? I want to do something like this:

def make_file():
yield "hello\n"
yield "world\n"

output = tarfile.TarFile(…)
stream = iterable_to_stream(make_file())
output.addfile(…, stream)

Answer Source

Here's my streaming iterator an experimental branch of urllib3 supporting streaming chunked request via iterables:

class IterStreamer(object):
    File-like streaming iterator.
    def __init__(self, generator):
        self.generator = generator
        self.iterator = iter(generator)
        self.leftover = ''

    def __len__(self):
        return self.generator.__len__()

    def __iter__(self):
        return self.iterator

    def next(self):
        return self.iterator.next()

    def read(self, size):
        data = self.leftover
        count = len(self.leftover)

        if count < size:
                while count < size:
                    chunk = self.next()
                    data += chunk
                    count += len(chunk)
            except StopIteration:

        self.leftover = data[size:]

        return data[:size]

Source with context: https://github.com/shazow/urllib3/blob/filepost-stream/urllib3/filepost.py#L23

Related unit tests: https://github.com/shazow/urllib3/blob/filepost-stream/test/test_filepost.py#L9

Alas this code hasn't made it into the stable branch yet as sizeless chunked requests are poorly supported, but it should be a good foundation for what you're trying to do. See the source link for examples showing how it can be used.