PythonWise: November 2008

Friday, November 14, 2008

The Code You Don't Write


Act without doing, work without effort.
Think of the small as large and the few as many.
Confront the difficult while it is still easy;
accomplish the great task by a series of small steps.
    - Lao-Tze

Sometimes, the code you don't write is more important than the one you write.
Whenever I start on a new task, my first question is "how can I do this without coding?".

Here's a small (true) exmaple:

We had a problem that serving files on an NFS mounted volume was slow for the first request and them it was good. Probably the mount went "stale" after a while.

First option of learning the inner working of NFS mounts was dropped immediately - you can never know how much time this tinkering will take and if it'll work eventually.

So I decided to keep the NFS mount "warm" by periodically accessing it.

First Version:

from time import sleep
from os import listdir

while 1:
    listdir("/path/to/nfs")
    sleep(10 * 60 * 60)

and in crontab


@reboot /usr/bin/python /path/to/script.py

Then I thought - "cron", and second version came:

from os import listdir

listdir("/path/to/nfs")</code></pre>

and in crontab:


*/10 * * * * /usr/bin/python /path/to/script.py

And then last version (just crontab):


*/10 * * * * /bin/ls /path/to/nfs

So down from 6 LOC to 3 LOC to 1 LOC - that's what I call produtivity :)

Saturday, November 08, 2008

Where is Miki?

A little CGI script that show where I am (gets data from my google calendar).

Using Google Data Python API

#!/usr/bin/env python
'''Where where am I? (data from Google calendar)

Get gdata from http://code.google.com/p/gdata-python-client/
'''

__author__ = "Miki Tebeka <miki.tebeka@gmail.com>"

import gdata.calendar.service as cal_service
from time import localtime, strptime, strftime, mktime, timezone

DAY = 24 * 60 * 60

def caltime_to_local(caltime):
    # 2008-11-07T23:30:00.000+02:00
    t = mktime(strptime(caltime[:16], "%Y-%m-%dT%H:%M"))
    tz_h, tz_m = map(int, caltime[-5:].split(":"))
    cal_tz = (tz_h * 60 * 60) + (tz_m * 60)
    if caltime[-6] == "-":
        cal_tz = -cal_tz

    # See timezone documentation, the sign is reversed
    diff = -timezone - cal_tz 

    return localtime(t + diff)

def iter_meetings():
    client = cal_service.CalendarService()
    client.email = "your-google-user-name"
    client.password = "your-google-password"
    client.source = "Where-is-Miki"
    client.ProgrammaticLogin()

    query = cal_service.CalendarEventQuery("default", "private", "full")
    query.start_min = strftime("%Y-%m-%d")
    tomorrow = localtime(mktime(localtime()) + DAY)
    query.start_max = strftime("%Y-%m-%d", tomorrow)
    feed = client.CalendarQuery(query)
    for event in feed.entry:
        title = event.title.text
        when = event.when[0]
        start = caltime_to_local(when.start_time)
        end = caltime_to_local(when.end_time)

        yield title, start, end

def find_meeting(meetings, now):
    for title, start, end in meetings:
        print title, start, end
        if start <= now <= end:
            return title, end

    return None, None

def meetings_html(meetings):
    if not meetings:
        return "No meetings today"

    trs = []
    tr = "<tr><td>%s</td><td>%s</td><td>%s</td></tr>"
    for title, start, end in meetings:
        start = strftime("%H:%M", start)
        end = strftime("%H:%M", end)
        trs.append(tr % (title, start, end))

    return "Today's meetings: <table border='1'>" + \
           "<tr><th>Title</th><th>Start</th><th>End</th></tr>" + \
            "\n".join(trs) + \
            "</table>"

HTML = '''
<html>
    <head>
        <title>Where is Miki?</title>
        <style>
            body, td, th {
                font-family: Monospace;
                font-size: 22px;
            }
        </style>
    </head>
    <body>
        <h1>Where is Miki?</h1>
        <p>
            Seems that he is <b>%s</b>.
        </p>
        <p>
            %s
        </p>
    </body>
</html>
'''

if __name__ == "__main__":
    import cgitb; cgitb.enable()
    from operator import itemgetter

    days = ["Mon","Tue","Wed", "Thu", "Fri", "Sat", "Sun"]
    now = localtime()

    day = days[now.tm_wday]
    meetings = sorted(iter_meetings(), key=itemgetter(-1))

    # Yeah, yeah - I get in early
    if (now.tm_hour < 6) or (now.tm_hour > 17):
        where = "at home"
    elif day in ["Sat", "Sun"]:
        where = "at home"
    else:
        title, end = find_meeting(now, meetings)
        if end:
            where = "meeting %s (until %s)" % (title, strftime("%H:%M", end))
        else:
            where = "at work"

    print "Content-Type: text/html\n"
    print HTML % (where, meetings_html(meetings))

Wednesday, November 05, 2008

Document With Examples

I've found out that a lot of times when I have a parsing code, it's best to document the methods with examples of the input.

A small example:

#!/usr/bin/env python
'''Simple script showing how to document with examples'''

__author__ = "Miki Tebeka <miki.tebeka@gmail.com>"

import re

# HTTP/1.1 200 OK
# HTTP/1.1 301 Moved Permanently
def http_code(line):
    return line.split()[1]

if __name__ == "__main__":
    print http_code("HTTP/1.1 301 Moved Permanently")

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