| ``ioutils`` - Input/output enhancements |
| ======================================= |
|
|
| .. automodule:: boltons.ioutils |
|
|
| Spooled Temporary Files |
| ----------------------- |
| Spooled Temporary Files are file-like objects that start out mapped to |
| in-memory objects, but automatically roll over to a temporary file once they |
| reach a certain (configurable) threshold. Unfortunately the built-in |
| SpooledTemporaryFile class in Python does not implement the exact API that some |
| common classes like StringIO do. SpooledTemporaryFile also spools all of it's |
| in-memory files as cStringIO instances. cStringIO instances cannot be |
| deep-copied, and they don't work with the zip library either. This along with |
| the incompatible api makes it useless for several use-cases. |
|
|
| To combat this but still gain the memory savings and usefulness of a true |
| spooled file-like-object, two custom classes have been implemented which have |
| a compatible API. |
|
|
| .. _spooledbytesio: |
|
|
| SpooledBytesIO |
| ^^^^^^^^^^^^^^ |
| .. autoclass:: boltons.ioutils.SpooledBytesIO |
|
|
| .. _spooledstringio: |
|
|
| SpooledStringIO |
| ^^^^^^^^^^^^^^^ |
| .. autoclass:: boltons.ioutils.SpooledStringIO |
|
|
|
|
| Examples |
| -------- |
| It's not uncommon to find excessive usage of StringIO in older Python code. A |
| SpooledTemporaryFile would be a nice replacement if one wanted to reduce memory |
| overhead, but unfortunately its api differs too much. This is a good candidate |
| for :ref:`spooledbytesio` as it is api compatible and thus may be used as a |
| drop-in replacement. |
|
|
| Old Code:: |
| |
| flo = StringIO() |
| flo.write(gigantic_string) |
|
|
| Updated:: |
| |
| from boltons.ioutils import SpooledBytesIO |
|
|
| flo = SpooledBytesIO() |
| flo.write(gigantic_string) |
|
|
|
|
| Another good use case is downloading a file from some remote location. It's |
| nice to keep it in memory if it's small, but writing a large file into memory |
| can make servers quite grumpy. If the file being downloaded happens to be a zip |
| file then things are worse. You can't use a normal SpooledTemporaryFile because |
| it isn't compatible. A :ref:`spooledbytesio` instance is a good alternative. |
| Here is a simple example using the requests library to download a zip file:: |
| |
| from zipfile import ZipFile |
|
|
| import requests |
| from boltons import ioutils |
|
|
| # Using a context manager with stream=True ensures the connection is closed. See: |
| # http://docs.python-requests.org/en/master/user/advanced/#body-content-workflow |
| with requests.get("http://127.0.0.1/test_file.zip", stream=True) as r: |
| if r.status_code == 200: |
| with ioutils.SpooledBytesIO() as flo: |
| for chunk in r.iter_content(chunk_size=64000): |
| flo.write(chunk) |
|
|
| flo.seek(0) |
|
|
| zip_doc = ZipFile(flo) |
|
|
| # Print all the files in the zip |
| print(zip_doc.namelist()) |
|
|
|
|
| Multiple Files |
| -------------- |
|
|
| .. _multifilereader: |
|
|
| MultiFileReader |
| ^^^^^^^^^^^^^^^ |
| .. autoclass:: boltons.ioutils.MultiFileReader |
|
|
