read_html and read_json should provide a cache

[c0indev3l]

Hello,

pandas.io.html.read_html should provide a cache such as what requests_cache provides
https://requests-cache.readthedocs.org/en/latest/

persistence into sqlite, mongodb, redis... is very convenient.

Maybe some other pandas functions could also use this cache mechanism.
pandas.io.json.read_json for example

This is what I do

import requests
import requests_cache
expire_after = 15*60 # expire_after=delay_second or None
requests_cache.install_cache('req_cache', backend='sqlite', expire_after=expire_after)
import json
import pandas as pd
from StringIO import StringIO

req = requests.get(url)
io = StringIO(req.content)
df = pd.read_html(io)

Kind regards

[jreback]

This is a nice feature, but I don't think should be part of core pandas. requests is not a dep currently of pandas.

A cookbook recipie or a small section in the io.rst docs would acceptable.

[c0indev3l]

Lot's of people are using Pandas inside IPython notebook (which is a great tool) so they don't care of request limits of an API (number of time you send a request to a server) but when you are using a script that you are modifying that's quite different. And in such a case a cache could be very useful. Sometimes cache can be dangerous because you will get obsolete data but that's the risk.

About requests it's a great library I like how it simplifies things but I also understand that adding a dep must be a deliberate decision.

I also wonder if you know others Pandas functions that could take benefits from such a feature.

[dalejung]

Instead of executing the script repeatedly in a new kernel, I would suggest using ipython and %run. Then you can split out your heavy data calls into a data.py module. This will cache using the normal python module system. If you're using something like vim, you can setup a hotkey to run your file into a tmux window.

.vimrc

autocmd FileType python map <buffer> <S-r> :w<CR>:!tmux send-keys -t ipython "\%time \%run %:p" enter<CR><CR>

runs the file in a tmux session named ipython.

[c0indev3l]

Thanks for this tips but you should admit that putting only requests_cache.install_cache('req_cache', backend='sqlite', expire_after=None) (or something similar) will be easier (especially when you do not know well the script is being worked on)

[cpcloud]

@c0indev3l I think your solution above is great. pandas plays well with others. We don't want to add any more deps (even optional ones) right now.

[jreback]

closing as not in pandas purview, though @c0indev3l if you'd like to doc your soln would be more than happy to put it in the cookbook

[femtotrader]

A quite clean solution to this could be to provide an other parameter (a requests.Session or a requests_cache.CachedSession) to _read function.

so we could have

def _read(obj, session=None):

instead of

def _read(obj):

so if no session is passed classic urlopen will be used but if session is not None session (either requests or requests_cache could be passed)

if _is_url(obj):
    if session is None:
        with urlopen(obj) as url:
            text = url.read()
    else:
        text = session.get(url).content

read_htmlshould also have this session parameter.

That's just my own experiment with https://github.com/femtotrader/pandas_datareaders

I added cache mechanism to nearly every Python Pandas DataReaders
(I'm still having some issue with FamaFrench). I faced this read_html issue with Yahoo Finance Options (frames = pd.read_html(url))

I think this issue should be linked to #8961 .