A breif introduction to python for the newbies

Tutorial.py

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		#Author : Kevin Nelson kpie314(at)gmail.com

from pylab import *
						#Tools for plotting and what not

import os
						#Operating system interface tools
import csv
						#Spread Sheet reader
b = True
n =  42

q = 'What kind of variable typing does python use?'
a = 'Lets just say python was designed with flexibility in mind.'

if(len(q)>n):
	print str(n) + ' is > the number of characters in "' + q + '"'
else:
	print q +' is longer than '+str(n) + 'characters' 

						# Above we see some basic closures in python
 
						# Notice the meaning of : & tabs, making {} available for other purposes ...
						#2 basic groups in python are  lists [] and dictionaries {}

_myDictionary = {}
for key in range(0,10):
	value=key**2
	_myDictionary[key]=value 

						#make a dictionary of squares 0 - > 10

print _myDictionary

						# if we want to reformat the way that a dictionary is printed we can define a method...\\

def printDictionary(Dictionary):
	for k in Dictionary:
		print str(k) +'\t'+ str(Dictionary[k])
	pass

printDictionary(_myDictionary)
	
						# now that we have seen how to use dictionaries in python lets do somthing with a list
def getPrimes(n):
	primes = [2] 
						# instantiates our list to a list of one element, 2
	k = 3
	while(len(primes) < n):
						# python uses the prefix function len(var) for lists dictionaries and strings  
		k2 = 0
		isprime=True	
						#Vacuously true assumption that every number is prime unless 
		while(primes[k2]**2<=k):
			if(k%primes[k2]==0):
				isprime=False
				break
			k2+=1		
		if(isprime):primes.append(k)
		k+=2
	return(primes)

print getPrimes(n)

try:
						#Python will run the code in the try block top to bottom and only excecute the except block when an error is encountered
	printDictionary(getPrimes(n))
except(IndexError):
	print('LIST is not Dictionary')

						#Now that we have a LIST of primes, we can't use our printDictionary fuction

def printList(List):
	k2=1
	ret=''
						#Returning a string gives us more flexibility as opposed to printing the contents in the function
	for k in List:
						#Iterating through each element of the list
		ret+=str(k2)+'\t'+str(k)+'\n'
		k2+=1
	return(ret)

print(printList(getPrimes(n)))
						#Python lets you nest your function calls.

def readFile(n,delim):
	Data={}
						# Data will be returned as the contents of a standard spreadsheet accessible with row and column number
	with open(n) as csvfile:
						#n is the string name of the file, or path to a file
		tableMain=csv.reader(csvfile,delimiter=delim)
		k=0
		for row in tableMain:
						#Converts the list of lists returned by default from csv.reader into a dictionary of lists [][] -> {[]}
			Data[k]=row
			k+=1			#Integer labels for the rows of the table.
	return(Data)

if not os.path.exists('PythonTutorial'):# Check if the folder 'PythonTutorial' exists
	os.makedirs('PythonTutorial')		# If not make it
os.chdir('PythonTutorial')			# Set 'PythonTutorial' as the working directory

OutPut = open('PythonTutorial.tsv',"w") #Open a file called 'PythonTutorial.tsv'
OutPut.write(printList(getPrimes(n)))		#Write a list of tab separated values to the file
OutPut.close()					#Close the file

printDictionary(readFile('PythonTutorial.tsv','\t')) # Read and reprint the file.

primes = getPrimes(n)
t = arange(0., float(len(primes)), 1.)
s = primes
plot(t, s)

xlabel('Primes')
ylabel('Values')
title('About as simple as it gets, folks')
grid(True)
savefig("primes.png")
show()

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