'Missing' Python 3 Package After Installation using pip3 in Ubuntu 15.10

I am working on a project related to Google Maps, and interested to use polyline package. My system is Ubuntu 15.10 (just recently upgraded). And as usual, I use pip3 to do the job:

root@Kirana:/usr/lib/python3/dist-packages# pip3 install polyline
Downloading/unpacking polyline
  Downloading polyline-1.1.tar.gz
  Running setup.py (path:/tmp/pip-build-l9ch5_49/polyline/setup.py) egg_info for package polyline
    
Requirement already satisfied (use --upgrade to upgrade): six==1.8.0 in /usr/local/lib/python3.5/dist-packages (from polyline)
Installing collected packages: polyline
  Running setup.py install for polyline
    
Successfully installed polyline
Cleaning up...

Virtual Environment in Python: virtualenv, pyenv, venv?

As you might already know, virtual environment is a nice way to create isolated environment needed for our project from the Python main installation. In this way, we can keep our main installation clean and not bloated with unused packages after the project concluded.

However, it is a little bit confusing  on what is the better way to create the virtual environment. Based on my research, at least three words come out: virtualenv, pyenv, and venv. What are they, and which one should I use?

Learning Virtualenv in Python

Good references:
1. http://simononsoftware.com/virtualenv-tutorial/
2. http://iamzed.com/2009/05/07/a-primer-on-virtualenv/

about virtualenvwrapper:
http://blog.fruiapps.com/2012/06/An-introductory-tutorial-to-python-virtualenv-and-virtualenvwrapper

Retrieve MP3 Metadata

I know, there are many modules can be used: eyeD3, mutagen, etc. But I think it is a good idea to understand first what is the concept of MP3 metadata.

Based on this Wikipedia article, the ID3v1 metadata container (which I used for this script) occupies 128 bytes beginning with the string TAG. The tag is placed at the end of the file to maintain compatibility with older media players.

ID3v1 consists of the following informations, including the bytes position:

for deeper information about ID3, including the extended tags, visit Wikipedia link above.

Just in case you haven't got this information yet, in Windows, you must read MP3 file as binary file, therefore you should use 'rb' for open function.

Here is my script:

import sys

filename = sys.argv[1]

fsock = open(filename, "rb", 0)
fsock.seek(-128,2) # get the last 128 bytes
tagdata = fsock.read(128)

fsock.close()

if tagdata[:3] == "TAG":
print "title\t: ", tagdata[3:33]
print "artist\t: ", tagdata[33:63]
print "album\t: ", tagdata[63:93]
print "year\t: ", tagdata[93:97]
print "comment\t: ", tagdata[97:126]
print "genre\t: ", tagdata[127:128]

HTML Parsing using HTMLParser

Simple script to get the video download link from here, which are hosted at archive.org
This script is adapted from here.

HTMLParser usage
from Python documentation:

Usage:
    p = HTMLParser()
    p.feed(data)
    ...
    p.close()

Start tags are handled by calling handle_starttag() or
handle_startendtag(); end tags by handle_endtag().  The
data between tags is passed from the parser to the derived class
by calling handle_data() with the data as argument (the data
may be split up in arbitrary chunks).  Entity references are
passed by calling handle_entityref() with the entity
reference as the argument.  Numeric character references are
passed to handle_charref() with the string containing the
reference as the argument.

import sys
import urllib
import HTMLParser
import re

class GetLinks(HTMLParser.HTMLParser):
    def handle_starttag(self,tag,attrs):
        if tag == 'a':
            for name,value in attrs:
                if name == 'href':
                    if re.search('ArabicLanguageCourseVideos',value):
                        print(value)
                    
gl = GetLinks()
url = 'http://www.lqtoronto.com/videodl.html'

urlconn = urllib.urlopen(url)

# read and put the downloaded html code into url content
urlcontents = urlconn.read()

# input the downloaded material into HTMLParser's member function 
# for parsing
gl.feed(urlcontents)

Socket Exception Handlers

Based on book 'Foundations of Python Network Programming' chapter 2.

Based on Python documentation, there are four socket exceptions (error, herror, gaierror, timeout). Here, I only use the socket.error only. It is used for general I/O and communication problems.

For an illustration, try the following from command line:

> python.exe socket.py google.com 80 index.html

import socket,sys

# standard input
host = sys.argv[1]
port = sys.argv[2]
filename = sys.argv[3]

# error handler 
def errorHandler(message,e):
    print('{0} {1}' .format(message,e))
    sys.exit(1)
    
# create socket 
try:
    s = socket.socket(socket.AF_INET,socket.SOCK_STREAM)
except socket.error, e:
    errorHandler('Socket creation error: ',e)

# input port manipulation
try:
    port = int(port)
except ValueError,e:
    errorHandler('Error port number: ',e)

# connection initiation
try:
    s.connect((host,port))
except socket.error, e:
    errorHandler('error socket initiation: ',e)
    
# sending HTTP request
try:
    s.sendall("GET %s HTTP/1.0\r\n\r\n" % filename)
except socket.error, e:
    errorHandler('Error sending HTTP request: ',e)
    
# receiving data from server
while 1:
    try:
        buf = s.recv(2048)
    except socket.error, e:
        errorHandler('Error receiving data: ',e)
    if not len(buf):
        break
    sys.stdout.write(buf)

Install zope.interface for Twisted

Twisted uses Zope Interface to define and document APIs.

1. Download it from here. It's in egg format. Choose the appropriate Python version with ours.
2. To install .egg, we need 'Easy Install' that is part of setuptools. So, we have to install setuptools first. Download it from here. Choose the appropriate Python version with ours. Because our aim is to be able to install .egg, choose setuptools in .exe format.
3. Run the installer. 
4. It will install a new executable file called 'easy_install.exe' under Python's 'Scripts' folder.
5. To install the zope.interface in .egg format, I did the following in Command Line:

c:\Python26\Scripts\easy_install.exe c:\zope.interface-3.6.1-py2.6-win32.egg

Now we can use the zope.interface for our twisted.

---
Further readings:

• Twisted.
• Python eggs.
• Easy Install.

Checking Input Type

The idea:
check whether input is numeric or not. First, try to convert the input into float object. If failed, then it is not numeric for sure :p

while True:
    try:
        radius = float(input('masukkan jari-jari lingkaran: '))
        break
    except ValueError:
        print('masukkan angka!')

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