PythonWise

If it won't be simple, it simply won't be. [source code] by Miki Tebeka, CEO, 353Solutions

Friday, January 09, 2015

python -m

python -m lets you run modules as scripts. If your module is just one .py file it'll be executed (which usually means code under if __name__ == '__main__'). If your module is a directory, Python will look for __main__.py (next to __init__.py) and will run it.

One of Python's mottoes is "batteries included", and this goes for python -m as well. Here are some (all?) of the gems hidden in the standard library. Sadly not all of them have help, but I poked around in the source code to see the usage.

json.tool

This is by far the one I use most, it'll indent nicely an JSON input in the standard output and very helpful in combination with curl.
$ curl -sL http://j.mp/1IuxaLD
[{"x":1,"y":2},{"x":3,"y":4},{"x":5,"y":6}]
$ curl -sL http://j.mp/1IuxaLD | python -m json.tool
[
    {
        "x": 1,
        "y": 2
    },
    {
        "x": 3,
        "y": 4
    },
    {
        "x": 5,
        "y": 6
    }
]

zipfile

zipfile will let you view, extract and create zip files - very much like the zip and unzip. Here's the help:
$ python -m zipfile -h
Usage:
    zipfile.py -l zipfile.zip        # Show listing of a zipfile
    zipfile.py -t zipfile.zip        # Test if a zipfile is valid
    zipfile.py -e zipfile.zip target # Extract zipfile into target dir
    zipfile.py -c zipfile.zip src ... # Create zipfile from sources

gzip

Like zipfile, let's you compress and decompress .gz files, like gzip/gunzip. By default it'll compress a file but with -d will decompress.
python -m gzip wordlist.txt  # Will create wordlist.txt.gz
python -m gzip -d wordlist.txt.gz  # Will extract to wordlist.txt

filecmp

Compare two directories.
$ python -m filecmp /tmp/a /tmp/b
diff /tmp/a /tmp/b
Only in /tmp/a : ['1']
Only in /tmp/b : ['2']
Identical files : ['4']
Differing files : ['3']

Encode/Decode

Several modules lets you encode/decode in various formats:
  • base64
  • uu
  • encodings.rot_13
  • binhex
  • mimify
  • quopri
For example
$ echo 'secertpassword' | python -m encodings.rot_13
frpregcnffjbeq

Servers

There are several servers that you can run, the ones I know are SimpleHTTPServer, CGIHTTPServer and smtpd (mail). If you quickly want to serve some files from a directory on your machine, just run:
python -m SimpleHTTPServer

Clients

Modules that provide simple clients to various protocols are:
  • ftplib
  • poplib
  • nttpserver
  • smtplib (on localhost only)
  • telnetlib
For example if you want to view Star Wars in text mode, do
$ python -m telnetlib towel.blinkenlights.nl

System Info

You can use platform to get some platform information (very much line uname -a) and locale to get locale information. Use mimetype to get the mime type of a file:
$ python -m mimetypes doc.html
type: text/html encoding: None

Python Utilties

  • compileall will compile all Python files to .pyc
  • dis will show bytecode for a file
  • pdb will start the Python debugger on a given file (see here)
  • pydoc will show documentation on a module/class/function
  • site will print some site information (sys.path, USER_BASE ...)
  • sysconfig will show many system related information (such as exec_prefix)
  • tabnanny will tell you of you mix tabs and spaces (like starting python with -t or -tt)
  • tokenize will print list of tokens in Python file
I mostly use pdb and pydoc, for example:
$ python -m pydoc os.remove
Help on built-in function remove in os:

os.remove = remove(...)
    remove(path)
    
    Remove a file (same as unlink(path)).

Profiling

There are several profiles and timers you can use from the command line:
  • cProfile - Show profile information
  • profile (use cProfile :)
  • timeit - Time how long things run
  • pstats - Print output of profiles
  • trace - Show tracing information on run
Example:
$ python -m cProfile match.py
         28537 function calls (27503 primitive calls) in 0.057 seconds

   Ordered by: standard name

   ncalls  tottime  percall  cumtime  percall filename:lineno(function)
        1    0.000    0.000    0.000    0.000 :1()
        1    0.000    0.000    0.000    0.000 :1(ArgInfo)
        1    0.000    0.000    0.000    0.000 :1(ArgSpec)
   ...

$ pyton -m timeit 'import math; math.factorial(100)'
100000 loops, best of 3: 12.9 usec per loop

timeit has good help from the command line.

IDLE

You can start IDLE by running python -m idlelib.idle

ensurepip

Python 2.7.9 and 3.x comes with an easy way to install pip. Run python -m ensurepip and pypi is at your service.


That's about it ... What are you favorite python -m tools? Which ones did I miss?

EDIT: The good folks at comp.lang.python reminded me a few I forgot:

unittest

python -m unittest discover will run unittest in discovery mode. Just drop a new Python file starting with test and it'll be picked up next time you run the tests. You can also specify a specific test to run with python -m unittest test_file.py TestClass.test_method.

calendar

python -m calendar will show calendar of the current year. You can also run python -m calendar YEAR to display a specific year and python -m calendar YEAR MONTH to display a specific month.

Easter Eggs

python -m this will display the Python Zen
python -m antigravity will open XKCD comic web page (which my company is named after).

Saturday, December 20, 2014

Quick View of matplotlib Styles

matploblit 1.4.2 added support for styles. I created a notebook to show how the ones bundled in look, you can view it here.

Wednesday, December 17, 2014

Calculate Distance in .kmz File

Here's a little script that calculates the distance of a path (series of GPS points) in a .kmz file (which I generate with My Tracks). It combines several elements - Zip file, XML (with namespaces), zip, sum and of course a bit of math.

Sunday, December 07, 2014

The Versatile date Command

*nix systems comes with a date command line utility. Many people use it to view the current time, however there's much more that date can do.

For example we run a daily job to process yesterday data. The job is a Python script that get the date as a paramter in YYYYMMDD format. This translates to one cron line:

@daily /path/to/job.py $(date --date=yesterday +%Y%m%d)

Here are some things you can do with date:


As a bonus, there is also a cal command which displays calender. Note that years are 4 digits so cal 4 14 will diaplay April for the year 14, not 2014.

cal has a handy -w switch that shows the work week as well.

Wednesday, November 26, 2014

Generate QR Code Using Google Charts API

Here's a small utility to generate QR code image using Google Charts API.

Note the hand crafted Python 2/3 support, for more advanced stuff you might want to have a look at six. However for this script I wanted to stay without external dependencies.

Sunday, November 16, 2014

Common Errors

"Experience is the name every one gives to their mistakes."
    - Oscar Wilde

Students are sometimes amazed by how I can tell the cause of exception without looking at the code. This is the result of making many errors in Python myself and also from observing many students doing mistakes. Here's a short list I've compiled of most likely cause of errors:

NameError

  • You forgot to import a module
  • You made a typo

AttributeError: 'NoneType' object has no attribute ...

  • You forgot a return in your function

AttributeError

  • Typo on dot lookup (obj.foo)
  • Object is different type from what you think (str vs int)
  • Object does not implement a dunder method (e.g. __len__)
There's also the 3'rd party didyoumean module, which might be interesting for beginners. It changes the default stack trace to add a hint about what might be the problem.

Monday, November 03, 2014

A Streaming Chart using Flask and flot

I was teaching a course on "Python Analytics" (pandas, scikit-learn, matplotlib ...) and was asked to provide an example of streaming chart - ones that updates periodically. I've showed a couple of examples one by generating image using matplotlib and another with bokeh-server. After a couple of days I remembered another way - using flot to render the chart. Here's a small example using Flask as the web server (the code works both on Python 2 and 3).


Few comments:

  • Don't use debug=True in production :)
  • For simplicity everything is in one file. However for larger application you might want to take the HTML template(s) out
  • Data is in memory, a restart will wipe it out. If you need data persistence - pick a database (shelve, sqlite3 ...)
  • A big shoutout to Continuum Analytics - Anaconda (and conda) has made my life so much easier teaching this workshop.

Blog Archive