Now on Github

HousewifeHacker is now on Github. To avoid further formatting problems with pasting my code on the blog, I will be using github to embed my code. For those who are unfamiliar with Github, the site allows programmers to follow open source contributions from different authors and contribute to full projects (Repositories) or small code snippets (Gists) by creating your own code or making changes to other user's work (forking). Users can determine whether their repositories and gists are public or private. The objective of Github is to serve as a social coding resource as well as a revision control. Because I want to be able to contribute to open source projects as I become more knowledgeable of Python, Github will become an increasingly valuable resource.

maketrans Python and Improved Caesar's Shift

Maketrans is used to translate strings, character for character. The characters can be symbols, letters, or numbers. The following short example is a Caesar's Shift moving backwards by two letters.

#first we need to import maketrans
>>> from string import maketrans
#now define the translation
#parameters are strings, not lists
#first parameter defines what will be found in the string
#second parameter defines what each will be changed to
>>> trans = maketrans('cdefg','abcde')
#define our string and translate
>>> s = 'deg'
>>> s.translate(trans)
'bce'

Now using maketrans and a few other suggestions from the comments, I have written a newly improved Caesar's Shift. Encode and decode use the same code, because a shift of 4 in one direction of a 26 character alphabet is equivalent to a shift of 22 in the other direction. I also used ascii_letters to shift my translation, which is 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ'. The letter w may be encoded to be a A by a shift of 4, but the decoding will return the lowercase w. There was an error in my exception handling, which is now corrected.

Caesar Cipher in Python Using ASCII

ASCII is how American computers store numbers, letters, certain commands, and symbols as numbers. A binary byte is eight digits long, consisting of only 1 and 0. When ASCII was developed, there were 2^8, or 256 possible characters for 8-bit (1 byte) personal computers. Unicode is used more commonly and extensively, but ASCII is sufficient or this exercise. Consult an ASCII Table or play with python's default functions to determine the encoding of a character such as 'a', 'A' or '&'.

In python, we can find the ascii value using ord of a string

>>> ord('a')
97
>>> ord('A')
65
>>> ord('b')
98
>>> ord('1')
49
>>> ord('2')
50
>>> 3-0
3
>>> ord('3')-ord('0')
3

Notice how the lower case and upper case are unique. Also, the ASCII numeric value and the character increase by the same amount. The same trend is true for the continuation of the alphabet, if lower case or upper case characteristic is preserved. The string length must be 1 when using ord, because each index has its own ASCII value.For a multiple digit number or a word, you can use a for loop to go through the string.

The reverse of ord is chr, for character.

>>> chr(97)
'a'
>>> i=97
>>> while i<104:
...   print chr(i)
...   i+=1
... 
a
b
c
d
e
f
g
>>> alpha=[]
>>> i=97
>>> while i<104:
...   alpha.append(chr(i))
...   i+=1
... 
>>> print alpha
['a', 'b', 'c', 'd', 'e', 'f', 'g']

Caesar's shift was how Caesar communicated with his generals, in which each letter in the plaintext is replaced by a letter some fixed number of positions down the alphabet. For example, if an 'a' is encoded by a 'c' with a shift of 2, then a 'b' would be encoded by a 'd.' Reversely, an 'a' in the encoded text would be a 'y' in the plaintext. The following program was inspired by thepythonchallenge.com. My husband and I had a lot of fun testing and debugging by sending each other messages over email. The code only changes letters so that spaces, smilies, brackets, and other punctuations and characters will be preserved. string.maketrans would be very useful and less code for a one time application, but the following code is highly reusable.

#string will later allow us to test for ascii letters
import string

def encode(input,shift):
  #create an empty string
  foo = ''
  #a for loop to shift the letters by the shift input 
  for x in input:
    #changes only ascii letters
    if x in string.ascii_letters:
      #upper case end of alphabet, to loop back to A
      if ord(x) > ord("Z") - shift and ord(x) <= ord("Z"):
        new_ord = ord(x) + shift - 26
      #lower case end of alphabet
      elif ord(x) > ord("z") - shift and ord(x) <= ord("z"):
        new_ord = ord(x) + shift - 26
      else:
        new_ord = ord(x) + shift
    #other characters will remain unchanged
    else:
      new_ord = ord(x)

    new_chr = chr(new_ord)
    foo += new_chr

  print "Your encoded message is ", foo

def decode(input,shift):
  #create an empty string
  foo = ''
  #a for loop to shift the leters by the shift input 
  for x in input:
    #changes only ascii letters
    if x in string.ascii_letters:
      #upper case start of alphabet, to loop back to Z
      if ord(x) - shift < ord("A")  and ord(x) >= ord("A"):
        new_ord = ord(x) - shift + 26
      #lower case end of alphabet
      elif ord(x) - shift < ord("a") and ord(x) >= ord("a"):
        new_ord = ord(x) - shift + 26
      else:
        new_ord = ord(x) - shift
    #other characters will remain unchanged
    else:
      new_ord = ord(x)
    new_chr = chr(new_ord)
    foo += new_chr
  print "Your decoded message is ", foo


def get_shift():
  try:
    shift = int(raw_input("How many characters do you want to\
 shift?\n"))
  except:
    print 'Shift must be a number'
    shift = get_shift()
  if not (shift > 0 and shift <= 25):
    print 'Shift must be between 1 and 25'
    shift = get_shift()
  return shift

def main():
  try:
    action=raw_input("Welcome to Caeser's Shifter! Would you \
like to encode or decode a message today?\n")
  except:
    print 'Please type encode or decode'
    main()
  shift = get_shift()

  print "Ok, let's %s your message with a shift of %d." % (action, shift)
  input=raw_input("What would you like to be translated?\n")

  if action=='encode':
    encode(input,shift)
  elif action=='decode':
    decode(input,shift)

if __name__ == "__main__":
  main()

There are probably a few areas where redundancy can be reduced, but I am still learning as a developer. This was my first time trying exception handling, which I learned from my husband.

' \ ' Escapes in Python

I have previously mentioned that '\n' codes for a new line. The backslash is known in Python as an escape.

>>> print "\tThis is a tabbed line"
 This is a tabbed line
>>> print "This sentence \nis split on \nthree lines"
This sentence 
is split on 
three lines
>>> print "Type \\ for a backslash"
Type \ for a backslash
>>> print "Verticle \vTab"
Verticle 
         Tab
>>> print "Shopping List: \vPrenatal vitamins \vCocoa Butter \
... \vOrange juice"
Shopping List: 
               Prenatal vitamins 
                                 Cocoa Butter 
                                              Orange juice
>>> print "Shopping List: \n\t*Prenatal vitamins \  
...\n\t*Cocoa Butter \n\t*Orange juice"
Shopping List: 
 *Prenatal vitamins 
 *Cocoa Butter 
 *Orange juice
>>> print 'Prevent the single quote 5\'5" from ending the string'
Prevent the single quote 5'5" from ending the string
>>> print "Prevent the double quote 5'5\" from ending the string"
Prevent the double quote 5'5" from ending the string

Notice that I also used a backslash in my string so that I could continue onto the next ine without Python thinking my string was done. There are other escapes in Python you can read about. "Carriage return" is a term from type writers to mean that you move to the beginning of a line. Linefeed and formfeed are also typewriter terms. \n and \t will be the most frequently used, though you may also want to be familiar with other escapes for unique problems.

Guess the Number Game Python

With inspiration from InventWithPython.com, I wrote a game to guess a number between 1 and 20 with six attempts. This simple game is good practice for a beginner. My code is written in Python 2.6. The example from the link is written in Python 3 syntax.

import random

guessesTaken = 0

print 'Hello! What is your name?'
myName = raw_input() #get user name

number = random.randint(1,20) #random number between 1 and 20
print '%s I am thinking of a number between 1 and 20.' % myName

while guessesTaken < 6:
  print 'Take a guess.'
  guess = int(raw_input())
  guessesTaken += 1
  if guess < number:
    print 'Your guess is too low.'
  elif guess > number:
    print 'Your guess is too high.'
  else:
    break #breaks out of loop

if guess == number:
  if guessesTaken == 1:
    print 'Good Job, %s! You guessed my number in 1 guess!'
  else:
    print 'Good Job, %s! You guessed my number in %d guesses!' % \
(myName,guessesTaken) #actual format on previous line without '\'


if guess != number:
  print 'No. The number I was thinking of was %d' % number

Python Debugger Article by Sontek

My husband wrote a wonderful blog post about debugging Python. Read it here.

String Formatting in Python

An easy way to combine strings with non strings is to use commas:

>>>>>> print 'The value of pi is often rounded to',3.14
The value of pi is often rounded to 3.14

But what if you want to create a website that welcomes guests by their name after he or she logs in? What if you are pulling information from a list or a dictionary? For personalization or multiple use functionality, we will be using string formatting. Below are the different format characters. There are a few others, but they aren't necessary.

%s   string
%d   integers or decimals, but returns floor integer
%r   anything that is not a string, converts object to a string
%f   floating point, so we can control precision after decimal

Here is an example of using each of the formats:

>>> name='Anderson Silva'
>>> weight= 105 #integer
>>> height= 1.92 #decimal, but I only want 1.9 displayed
>>> home= 'Brazil' #string, watch what happens with %r 
>>> fighter1='''%s
... Nationality: %r
... Weight: %d kg
... Height %.1f m''' % (name,home,weight,height) #in order 
>>> print fighter1
Anderson Silva
Nationality: 'Brazil' #%r leaves quotes around strings
Weight: 105 kg
Height 1.9 m

Here is an example converting centimetres to inches

>>> def convert(cm):
...  inches=cm*.39370
...  print 'There are %.2f inches in %d centimetres' % (inches,cm)
... 
>>> convert(10)
There are 3.94 inches in 10 centimetres 
>>>#two places after decimal are shown
>>> convert(3.544445)
There are 1.40 inches in 3 centimetres

%f has a default to print six numbers after the decimal. By adding '.1', '.2', '.3', etc... between the '%' and 'f', you determine how many numbers are visible after the decimal. You can also add '+' or '-' before the '.x', such as showing a change

>>> print "Today's stock price changed %+.2f" % 1.4888
Today's stock price changed +1.49

Decimal Library for Changing Number Precision in Python

The built in math functions in Python use binary approximations, giving some funky results when dealing with numbers containing decimals:

>>> .1+.2
0.30000000000000004
>>> round(100.00/3.000,4)
33.333300000000001

One way to appropriately find the sum of decimals is to use strings

>>> str(.1+.2)
'0.3'

Also, the default is to round to the nearest whole number when dividing

>>> 1/3
0
>>> 100/3
33

The decimal library is a useful tool for floating point arithmetic. Instead of the command 'from decimal import *' that would import everything from decimal, all I need to import is Decimal and getcontext. When importing modules, simplicity is preferred. There are less problems with naming in your code and you can be more aware of the tools at your disposal. I already imported decimal and looked through the directory to determine which modules I wanted. I'm only going to show the precision feature of decimal. You may want to import the entire library if you want to use other functions.

>>> from decimal import getcontext
>>> from decimal import Decimal
>>> getcontext()
Context(prec=28, rounding=ROUND_HALF_UP, Emin=-999999999, 
Emax=999999999, capitals=1, flags=[Inexact, Rounded], 
traps=[DivisionByZero, Overflow, InvalidOperation])
>>> #our precision is also known as significant figures, 
applied after arithmetic 
... #let's change our precision
... 
>>> getcontext().prec=6
>>> Decimal('1')/Decimal('7') #can be performed to strings
Decimal('0.142857')
>>> Decimal(1)/Decimal(7) #can be performed to integers
Decimal('0.142857')
>>> Decimal(10)/Decimal(7)
Decimal('1.42857') #notice that 6 is the total number of 
figures, not the number after the decimal
>>> Decimal(10)/Decimal(5)
Decimal('2') #not '2.00000,' which is considered more 
accurate than 2 by the science community

As someone with a science background, I found the decimal library's use of 'significant figures' interesting. Decimal can also be used in financial reporting or billing. You can also find maximums and minimums, change rounding properties, and do anything that you can do with the math library. I personally prefer the math library for the algebraic functions performed by decimal, because math's syntax is simpler. To learn more about decimal, click here .

Using Map Function in Python

Today I discovered the map function in Python. Map causes some simple for loops to be verbose and unnecessary. Let's look at how to change a list of integers to a list of strings. First we'll use a for loop:

>>> list=[1,2,3,4,5]
>>> index=0
>>> for x in list:
...   list[index]=str(list[index])
...   index+=1
... 
>>> print list
['1', '2', '3', '4', '5']

Now we'll use the map function and we'll define our 1-5 list using the range function

>>> list1=range(1,6)
>>> map(str,list1) #performs str function to every index of list1
['1', '2', '3', '4', '5'] 

You can also make your list within the map function, such as splitting a string into a list. The following example shows how you can define a method using else, elif (else if), and if statements, then run your method to a single string with the map function, resulting in a list with the method performed to each index.

>>> def pluralize(word):
...   if word[-1]=='y':
...     return word[:len(word)-1]+'ies' #replaces the y with ies
...   elif word[-1]=='s':
...     return word+'es'
...   else:
...     return word+'s'
... 
>>> map(pluralize, "The sexy waitress brought me a beer".split()) 
['Thes', 'sexies', 'waitresses', 'broughts', 'mes', 'as', 'beers']
>>>#my husband chose the sentence

I simplified my method to not account for every scenario put into it. Although this specific example does not produce correct English, the map function correctly split the string on the whitespace and carried out the method on each index of the list.

Indexes, Strings and Lists in Python

A Python string's properties can be best understood by using sentences and words, although numbers can also be stored as strings. Be careful not to name a string as 'str' or 'string', because these are built in functions in Python. Let's play with some basic functions you can do to strings

[gypsychemist@inspidell ~]$ python
Python 2.6.4 (r264:75706, Jun  4 2010, 18:20:16) 
[GCC 4.4.4 20100503 (Red Hat 4.4.4-2)] on linux2
Type "help", "copyright", "credits" or "license" for more 
information.
>>> sentence1='This is two strings '
>>> sentence2='combined.'
>>> sentence1+sentence2
'This is two strings combined.'
>>> s=sentence1+sentence2
>>> print s
This is two strings combined.
>>> r='''Three quotes will
... preserve the formatting
... for multiple lines'''
>>> print r
Three quotes will
preserve the formatting
for multiple lines 
>>> s.split()
['This', 'is', 'two', 'strings', 'combined.']
>>> r.split('e')
['Thr', '', ' quot', 's will\npr', 's', 'rv', ' th', 
' formatting\nfor multipl', ' lin', 's']

The split command divides a string into a list based on the delimiter you define. In the example of splitting the s string, leaving the delimiter blank causes splitting on all white spaces (tab, enter, space). Anything can be the delimiter, such as using 'e' in the splitting of r example. '\n' is a new line.

>>> p="  The extra white space on the ends     "
>>> p.strip()+' is removed by the strip function'
'The extra white space on the ends is removed by the 
strip function'

Indexes are useful for both strings and lists. A common graphic to explain indexes is:

The letters or numbers in a string begin with the index 0, or you can work from the back with index of -1. When selecting a range of indexes, the last number is excluded.

>>> f='hello'
>>> f[0:2]
'he'
>>> f[:2] #a starting index of 0 is assumed
'he'
>>> f[2]
'l'
>>> f[-2:] #completing until the end is assumed
'lo'
>>> f[-2:-1]
'l'
>>> f[:2]+f[-2:]
'helo'
>>> list=[0,1,2,3,4,5]
>>> list[1]
1
>>> list[-2:0] #doesn't work
[]
>>> list[-2:]
[4, 5]
>>> list[:1]
[0]
>>> 

'#' is used in Python to write comments. They are ignored in programs and are very useful to solve problems, either to write out a plan or to type in a literal translation of how you expect your code to perform. If your code does not work correctly, you can go back through your notes to quickly find where your logic or syntax may be incorrect.

As I mentioned briefly in the beginning, a number can also be a string. If a number is a string, it will be used a returned with quotation marks surrounding it. In Python, single quotes and double quotes act the same; however, the opening and closing ends need to be the same. The example below shows why you may want to change a number to a string:

>>> pi=3.14
>>> # cannot add an integer to a string
>>> print 'The value of pi is often rounded to ' + pi 
Traceback (most recent call last):
  File "", line 1, in 
TypeError: cannot concatenate 'str' and 'float' objects
>>> #so we change pi to a string
>>>print 'The value of pi is often rounded to ' + str(pi) 
The value of pi is often rounded to 3.14
>>> #you can include a number after a string by using a comma
>>>print 'The value of pi is often rounded to',3.14
The value of pi is often rounded to 3.14

You can change a list of numbers to be a list of strings by using a for loop.

>>> list=[1,2,3,4,5]
>>> str(list[1]) #returns the list index as a string without 
changing the list
'2'
>>> list #list is still composed of integers
[1, 2, 3, 4, 5]
>>> index = 0 #we're setting a variable to start at 0 because
 index starts at 0
>>> for x in list: #begins with index 0
...   list[index] = str(list[index]) #assigns index 0 integer as 
a string of the previous list[0]
...   index += 1 #after the previous command is performed on [0],
 it will be performed on [1]
...   #for loop continues through indexes 1 to 4 after index 0
>>> list #our list is now changed to be strings
['1', '2', '3', '4', '5']

Now lets play with some list commands that are nondiscriminate against strings or integers:

>>> list1=['8','9','10']
>>> list.extend(list1) #add list1 to end of list, list+list1
>>> print list
['3', '4', '5', '6', '7', '8', '9', '10']
>>> list.insert(2,'3') #inserts '3' at index 2
>>> print list
['3', '4', '3', '5', '6', '7', '8', '9', '10']
>>> list.insert(2,3) #now we'll insert an integer
>>> print list #list can have combination of strings & non strings
['3', '4', 3, '3', '5', '6', '7', '8', '9', '10']

For more documentation and to try writing example programs, visit Google's Python classroom: http://code.google.com/edu/languages/google-python-class/index.html

Math with Python

If this is your first time using Python in Windows, you will have to download it from python.org. Every operating system includes a terminal, which we will be using to practice and test. Google "How to open terminal" and your operating system name to find specific information about opening your terminal. You will also need either VIM, WING, Eclipse, or another editor to save and run your programs, though we do not need to use it for this tutorial. This article will focus on math capabilities within Python, either performing calculations as a common calculator or within logic commands. So open your terminal and play with me.

I start my code with telling my terminal that I would be working in python. [gypsychemist@inspidell ~]$ is my shell prompt, "python" is what I typed, and the next three lines are showing that python is installed and open for me to use.

[gypsychemist@inspidell ~]$ python
Python 2.6.4 (r264:75706, Jun  4 2010, 18:20:16) 
[GCC 4.4.4 20100503 (Red Hat 4.4.4-2)] on linux2
Type "help", "copyright", "credits" or "license" for more
information.
>>> 3+2
5
>>> 3*2
6
>>> 6/2
3
>>> 3-2
1
>>> 3*(3-1)
6 
>>> pi=3.14
>>> 3*pi
9.4199999999999999
>>> abs(2-3)
1
>>> pow(3,2)
9
>>> 3**2
9
>>> 

Basic math commands are shown above. '+' is for addition, '-' for subtraction. '*' for multiplication, and '/' for division. The basic math rules regarding parenthesis and order of operations are followed correctly. You can also store numbers as words or letters to perform math equations on, such as the example with pi. In Python, '=' is used to assign and does not imply equivalency. The absolute value function and two alternative ways to find a number with an exponent (also known as power) are shown.

A useful tool in python is the math library. To see the functions you can use within math, type 'import math' and 'dir(math)' on the next line. You just told the terminal you are opening the library and viewing the directory. The terminal will show you the commands including different trigonometric functions, advanced algebra, and rounding options. To learn more about a command (such as floor rounding), you can type 'help(math.floor)'. Press 'q' to exit help.

>>> import math
>>> dir(math)
['__doc__', '__file__', '__name__', '__package__', 'acos', 'acosh', 
'asin', 'asinh', 'atan', 'atan2', 'atanh', 'ceil', 'copysign','cos', 
'cosh', 'degrees', 'e', 'exp', 'fabs', 'factorial', 'floor', 'fmod', 
'frexp', 'fsum', 'hypot', 'isinf', 'isnan', 'ldexp', 'log', 'log10', 
'log1p', 'modf', 'pi', 'pow', 'radians', 'sin', 'sinh', 'sqrt', 
'tan', 'tanh', 'trunc']
>>> help(math.floor)
>>> math.floor(4.5)
4.0

You can also test to determine if one number is divisible by another, such as when you want to execute commands on only the even indexes in a list. To determine if 3 is evenly divisible by 2, type '3 %2'. Python returns '1' because there is a remainder of 1 when you divide 3 by 2. If 0 is a result, then numbers are evenly divisible.

>>> 3%2
1
>>> 3%3
0

If given a list of numbers and you want to perform math functions such as adding the numbers together, you can use a for loop. Follow the below example:

>>> list=[2,3,6,7,4,6]
>>> sum=0
>>> for x in list:
...   sum+=x
... 
>>> sum
28
>>> 

In Python, spacing of indentions and capitalization are very important. After any statement ending with ':' , indent by a consistent amount (two spaces, four spaces, tab, your choice).'sum+=x' is the same as 'sum=sum+x'. 'x' is the value at the index as it goes through the list. So this code just said 0+2+3+6+7+4+6=28. Now that you understand how to do it with a basic for loop, the quicker way is to use the built in sum function. Because I used the variable 'sum', already, I need to first reinstate sum to its built in function.

>>> from __builtin__ import sum
>>> sum(list)
28

Using built in functions as variables should be avoided. As you learn more Python, you will learn safe and understandable variables to use in your code. For more information on numbers and math, you can visit http://docs.python.org/library/numeric.html

CS Degree and Other Qualifications

Don't believe the infomercials or college recruiters. You do not need a college degree to have a career in computer programming. You may want a degree to get a management position overseeing programmers, but it is possible for skilled programmers with less than a year of college to be offered six figure management positions after five years of employment in the industry. There are employers who are more sceptical of hiring college graduates than hobbyists. Such employers prefer people who have worked on open source projects. Open source projects are contribution efforts from many programmers, so the code is available to the masses and programmers do not make money from their efforts. Most college courses in computer science focus on old technologies and obsolete techniques. Hobbyists take advantage of other opportunities to learn and usually enjoy expanding their knowledge and skills through practical experience. There are plenty of online books and 'classrooms' to learn from for free. As my husband has told me, "Programmers control the internet." When you google a term that is in programming, your first couple hits will be programming tutorials, blogs, and discussions. As you feel more comfortable with basic programming, you can expand your knowledge from reading blogs, buying books, participating in user groups, and attending conferences.

As with any job or profession, you need to consider your personality, skills, interests, lifestyle, and values to determine if you will be happy and have the capability to excel. In terms of personality, most computer programmers are introverts. 'Introvert' does not mean a social outcast; an introvert enjoys time to themselves or less than three others, does not need a lot of noise and external stimuli to stay entertained, and usually analyzes what they plan to do and say before carrying out their actions. Computer programmers are very analytical. Syntax and logic are the basic necessities for every computing language. An interest in computers and technology is beneficial, but a lot of knowledge about hardware and operating systems is not necessary to begin programming. The industry you choose to work within as a programmer will be affected by your lifestyle, interests, values, and often preferred programming languages. My dad has chosen to work in a management role within the healthcare industry. My husband still enjoys coding, so he works on registration software for conferences. Nearly every industry requires software or websites, so there are many opportunities for computer programmers. You can choose to develop your own projects into a business, work in an office with colleages, or communicate with the office through conference calls from your own bed each morning.

My computer programming experience is very young. I will be using this blog to motivate myself to continue learning. The languages I want to learn are Python and Objective C. My reasons for wanting to learn these languages are so that I can pick up contract work as extra income and so that I can work on personal projects and companies with my husband.