dev.enekoalonso.com » python

Python script: remove empty folders

Eneko Alonso — Sat, 06 Aug 2011 17:07:25 +0000

One of the scripts I often use is this one to remove empty folders under a specific location on your hard drive. The usage is simple:

$ [path to the script]/remove_empty_folders.py [path_to_clean]

Here is the code:

#! /usr/bin/env python
import os, sys
def removeEmptyFolders(path):
if not os.path.isdir(path):
return
# remove empty subfolders
files = os.listdir(path)
if len(files):
for f in files:
fullpath = os.path.join(path, f)
if os.path.isdir(fullpath):
removeEmptyFolders(fullpath)
# if folder empty, delete it
files = os.listdir(path)
if len(files) == 0:
print "Removing empty folder:", path
os.rmdir(path)
removeEmptyFolders(sys.argv[1])

Here is a sample output:

Removing empty folder: ./assorted/2010/12/13/20101213-202802
Removing empty folder: ./assorted/2010/12/13
Removing empty folder: ./assorted/2010/12/14/20101214-120800
Removing empty folder: ./assorted/2010/12/14
Removing empty folder: ./assorted/2010/12/01/20101201-070118
Removing empty folder: ./assorted/2010/12/01/20101201-070111
Removing empty folder: ./assorted/2010/12/01/20101201-070123
Removing empty folder: ./assorted/2010/12/01
Removing empty folder: ./assorted/2010/12

Please, use at your own risk. It should work on Windows also, but I have not tested it.

Enjoy!

September 9, 2009 -- Crawling sitemaps with Python (0)
October 12, 2011 -- Command line scripting with Node.js (0)
August 18, 2010 -- Little tricks: repeating strings in Javascript & Python (1)
July 1, 2010 -- Little tricks: editing strings by index in Javascript and Python (1)

Little tricks: repeating strings in Javascript & Python

Eneko Alonso — Wed, 18 Aug 2010 19:17:34 +0000

How many times have you found yourself printing strings like “————-” or “===========”? I do that a lot when I have to do console.logs or if I’m working on a console application or script. Adding dividers to the output makes it more readable.

Python has a very peculiar syntax for repeating strings, which consists in just multiplying the string by a number, like this:

"123"*4 // returns "123123123123"

We can achieve the same in Javascript using Array.join() like this:

Array(4).join("123"); // returns "123123123123"
Array(30).join("-"); // returns "——————————"
Array(2).join("test"); // returns "testtest"

Very useful for logs or to generate repeated html strings, etc.

July 1, 2010 -- Little tricks: editing strings by index in Javascript and Python (1)
August 12, 2010 -- Little tricks: concatenating arrays in Javascript (4)
July 20, 2010 -- Little tricks: string padding in Javascript (3)
May 22, 2010 -- More WebSockets, now with Python! (9)

Little tricks: editing strings by index in Javascript and Python

Eneko Alonso — Thu, 01 Jul 2010 16:57:04 +0000

Editing strings by index maybe something that we don’t do all the time. But it’s one of these things that, coming from languages like C, one would assume is as trivial as assigning the value of an indexed position. Something like this:

var a = "hello world"
a[0] = "H"
console.log(a) // outputs "hello world"

Go ahead and paste that code in your favorite javascript console. You would expect the output to be “Hello there”, but it is not.
Same goes with Python, check this code:

>>> a = "hello world"
>>> a[0] = "H"
Traceback (most recent call last):
File "", line 1, in <module>
TypeError: 'str' object does not support item assignment
>>> a[0] = 'H'
Traceback (most recent call last):
File "", line 1, in <module>
TypeError: 'str' object does not support item assignment

This is because strings are read only and cannot be modified at all. Only replaced with new strings.

The solution: convert to array and back to string

There may be other solutions out there, I’m sure, but this is the solution I use: Both in Python and Javascript, a string can be converted into an array or list of characters (actually, list of strings). Then we can modify values by index and finally join the output into a new string.

Javascript:

var a = "hello world"
a = a.split("")
a[0] = "H"
a = a.join("")
console.log(a) // outputs "Hello world"

Python:

>>> a = "hello world"
>>> a = list(a)
>>> a[0] = "H"
>>> a = "".join(a)
>>> a
'Hello world'

It’s interesting to see how the syntax for joining arrays into strings is totally the opposite in Javascript and Python. In Javascript, join() is a function of the Array object while in Python join() is a function of the string class.

In the other hand, split() is a method of the String object in Javascript. There is a split() function on the string class in Python, but it cannot be used to split strings without a specific separator. The list() function/constructor does the trick.

August 18, 2010 -- Little tricks: repeating strings in Javascript & Python (1)
July 20, 2010 -- Little tricks: string padding in Javascript (3)
May 22, 2010 -- More WebSockets, now with Python! (9)
September 2, 2009 -- Creating HTML blocks with Mootools (4)

More WebSockets, now with Python!

Eneko Alonso — Sun, 23 May 2010 06:41:27 +0000

A couple of weeks ago, Tim and I worked on a little game/demo using WebSockets and C# (I haven’t been able to put it online since I do not have a Windows server). It was a lot of fun and we were able to see the potential of WebSockets and how much internet ~~can~~ will change in the next few years because of them.

Today I spent a couple of hours researching and implementing a WebSocket solution that I could run in my linux servers, and I found this very nice tutorial for creating a Python WebSockets server: http://yz.mit.edu/wp/web-sockets-tutorial-with-simple-python-server/

So I took that code and modified to create a very, very basic chat, that broadcasts received messages to all connected clients. You can try it here (as long as the python server is still up): http://enekoalonso.com/research/html5/websockets/python/

Here is the client code:

var form = document.getElementById('form');
var msg = document.getElementById('msg');
var output = document.getElementById('serveroutput');
var s = new WebSocket("ws://"+window.location.hostname+":9876/");
s.onopen = function(e) {
console.log("opened");
out('Connected.');
}
s.onclose = function(e) {
console.log("closed");
out('Connection closed.');
}
s.onmessage = function(e) {
console.log("got: " + e.data);
out(e.data);
}
form.onsubmit = function(e) {
e.preventDefault();
msg.value = '';
window.scrollTop = window.scrollHeight;
}
function sendMsg() {
s.send(msg.value);
}
function out(text) {
var el = document.createElement('p');
el.innerHTML = text;
output.appendChild(el);
}
msg.focus();

And the server code:

#!/usr/bin/env python
import socket, threading
# httphost = "localhost:8888"
# sockethost = "localhost:9876"
httphost = "enekoalonso.com"
sockethost = "enekoalonso.com:9876"
def handle(s, addr):
handsake = "HTTP/1.1 101 Web Socket Protocol Handshake\r\nUpgrade: WebSocket\r\nConnection: Upgrade\r\nWebSocket-Origin: http://%s\r\nWebSocket-Location: ws://%s/\r\nWebSocket-Protocol: sample\r\n\r\n" % (httphost, sockethost)
s.send(handsake)
data = s.recv(1024)
lock = threading.Lock()
while 1:
data = s.recv(1024)
if not data: break
print 'Data from', addr, ':', data
lock.acquire()
[conn.send(data) for conn in clients]
lock.release()
print 'Client closed:', addr
lock.acquire()
clients.remove(s)
lock.release()
s.close()
def start_server():
s = socket.socket()
s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
s.bind(('', 9876))
s.listen(1)
while 1:
conn, addr = s.accept()
print 'Connected by', addr
clients.append(conn)
threading.Thread(target = handle, args = (conn,addr)).start()
clients = []
start_server()

Check the live demo (be aware WebSockets are only supported by Google Chrome right now): http://enekoalonso.com/research/html5/websockets/python/
Open a few tabs and send some text. You should see it appearing in all of them. It will also work if you open the page in multiple browser windows or even if you open the page in different computers.

May 3, 2010 -- Playing with WebSockets (4)
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February 19, 2010 -- Having fun with Mooml & Twitter (0)
May 18, 2011 -- location.hash is dead (on html5 browsers) (0)

Crawling sitemaps with Python

Eneko Alonso — Wed, 09 Sep 2009 21:59:08 +0000

This a basic script I have created to crawl an xml sitemap file (does not support nested sitemaps). It will report if the request was successfully processed by the server or if, instead, it returned some kind of error.

#!/usr/bin/env python
from sys import argv
from re import findall
from socket import setdefaulttimeout
from urllib2 import Request, urlopen
from datetime import datetime
# Initialization
procId = argv[2]
sitemapUrl = argv[1]
print '[%s]'%procId, "Crawling sitemap:", sitemapUrl
# Test url
def testURL(url):
start = datetime.now()
msg = ''
code = -1
req = Request(url)
try:
response = urlopen(req)
code = response.code
except IOError, e:
if hasattr(e, 'reason'):
msg = '[Error: %s]' % e.reason
elif hasattr(e, 'code'):
msg = '[Error: %s]' % e.code
delta = datetime.now() – start
print '[%02s]'%procId, '[%d]'%code, '[%03dms]'%(delta.microseconds/1000), msg, '>>', url
return
# Load sitemap and process
req = Request(sitemapUrl)
htmlSource = urlopen(req).read()
linksList = findall('(.*?)', htmlSource)
print len(linksList), "links found."
for link in linksList:
testURL(link)

The script expects 2 parameters, the url for the xml sitemap and a identifier that will be printed to the log.

It is not very fast, but you can easily run multiple instances from the command line:

./sitemap_crawler.py http://example.com/sitemap.xml 1 &
./sitemap_crawler.py http://example.com/sitemap.xml 2 &
./sitemap_crawler.py http://example.com/sitemap.xml 3 &
./sitemap_crawler.py http://example.com/sitemap.xml 4 &
./sitemap_crawler.py http://example.com/sitemap.xml 5 &

Enjoy!

August 6, 2011 -- Python script: remove empty folders (1)
October 12, 2011 -- Command line scripting with Node.js (0)
May 18, 2011 -- location.hash is dead (on html5 browsers) (0)
August 18, 2010 -- Little tricks: repeating strings in Javascript & Python (1)

I’m ready for some fun with Python 3.0

Eneko Alonso — Sun, 07 Dec 2008 00:55:10 +0000

I just found out Python 3.0/3k has been finally released. This is very good news :) Let’s find out how to install it on Mac OS X Leopard.

August 6, 2011 -- Python script: remove empty folders (1)
August 18, 2010 -- Little tricks: repeating strings in Javascript & Python (1)
July 1, 2010 -- Little tricks: editing strings by index in Javascript and Python (1)
May 22, 2010 -- More WebSockets, now with Python! (9)

Making your objects sortable

Eneko Alonso — Sat, 29 Nov 2008 07:44:12 +0000

Making your objects sortable in Python is very simple: add the __cmp__ function and the logic to compare the two objects and you are done!

class person:
def __init__(self, name, age):
self.name = name
self.age = age
def __str__(self):
return 'Person %s (%d)' % (self.name, self.age)
def __cmp__(self, other):
return cmp(self.name+str(self.age), other.name+str(other.age))
lista = [
person('Ren Smith', 24),
person('Aohn Doe', 31),
person('Aohn Doe', 22),
person('Eneko Alonso', 30),
person('Ren Gomas', 34)
]
for person in lista:
print person
print '—–'
for person in sorted(lista):
print person

As you can see, you can totally customize your __cmp__ method and compare any class members.

Download the code: http://enekoalonso.com/svn/python/classes/sorting-objects.py

August 6, 2011 -- Python script: remove empty folders (1)
August 18, 2010 -- Little tricks: repeating strings in Javascript & Python (1)
July 1, 2010 -- Little tricks: editing strings by index in Javascript and Python (1)
May 22, 2010 -- More WebSockets, now with Python! (9)

Copying objects vs. copying references

Eneko Alonso — Thu, 27 Nov 2008 07:16:14 +0000

C++ is a language that allows creation of static instances of objects, this is without using pointers. This is why copy-constructors are needed, since it is common to copy or clone objects. Other languages like Delphi don’t allow to create static variables to instantiate objects. Instead, all objects are pointers. So in C++, assignments of instances of the same class create a copy of the object, while in Delphi, only the reference to the second instance is copied.

When I started learning Python one year ago, I wanted to know if objects were cloned on assignments or if only the reference to the object was assigned instead. Here is how I found it:

class Item():
def __init__ (self):
self.text = ""
def sayIt(self):
print self.text
A = Item()
B = Item()
A.text = "testing A"
B.text = "testing B"
A.sayIt()
B.sayIt()
A = B
A.sayIt()
B.sayIt()
A.text = "testing A 2"
A.sayIt()
B.sayIt()

This code will output 6 messages. The first two will be obviously different, since A and B are to separate instances on memory. When B is assigned to A, two things can happen. B is cloned and A is a new instance equal to B or the reference to B is assigned to A so A and B become the same instance in memory (B). No matter which one happens, both messages after the assignment will correspond to the B instance (“testing B”).

But what will happen when we modify A again? Will B be also modified?

Here is the output:

testing A
testing B
testing B
testing B
testing A 2
testing A 2

So A and B are now the same object in memory.

August 6, 2011 -- Python script: remove empty folders (1)
August 18, 2010 -- Little tricks: repeating strings in Javascript & Python (1)
July 1, 2010 -- Little tricks: editing strings by index in Javascript and Python (1)
May 22, 2010 -- More WebSockets, now with Python! (9)

Fibonacci

Eneko Alonso — Thu, 27 Nov 2008 06:08:10 +0000

Fibonacci is a fast growing sequence that can easily overflow your integer variables. Fortunately, Python doesn’t have this problem, since it can handle huge integer numbers.

#!/usr/bin/env python
def fib(n):
if n==0 or n==1:
ret = n
else:
ret = fib(n-1) + fib(n-2)
return ret
for i in range(1000):
print fib(i)

The example avobe has a big performance issue, due to the recursive calls to calculate n-1 and n-2 values, which are calculated multiple times over and over. By storing the results on a list we solve this issue, although we now relay on the amount of available memory.

#!/usr/bin/env python
fibs = []
def fib(n):
if n==0 or n==1:
ret = n
elif n < len(fibs):
ret = fibs[n]
else:
ret = fib(n-1) + fib(n-2)
fibs.append(ret)
return ret
for i in range(1000):
print fib(i)

Thus, Fib(1000) = 43,466,557,686,937,456,435,688,527,675,040,625,802,
564,660,517,371,780,402,481,729,089,536,555,417,949,051,890,403,879,840,079,
255,169,295,922,593,080,322,634,775,209,689,623,239,873,322,471,161,642,996,
440,906,533,187,938,298,969,649,928,516,003,704,476,137,795,166,849,228,875

August 6, 2011 -- Python script: remove empty folders (1)
August 18, 2010 -- Little tricks: repeating strings in Javascript & Python (1)
July 1, 2010 -- Little tricks: editing strings by index in Javascript and Python (1)
May 22, 2010 -- More WebSockets, now with Python! (9)

dev.enekoalonso.com » python

Python script: remove empty folders

Related Posts:

Little tricks: repeating strings in Javascript & Python

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Little tricks: editing strings by index in Javascript and Python

The solution: convert to array and back to string

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More WebSockets, now with Python!

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Crawling sitemaps with Python

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I’m ready for some fun with Python 3.0

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Making your objects sortable

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Copying objects vs. copying references

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Fibonacci

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