# global vs local examples

# num1 is a global variable

num1 = 1

print num1

# num2 is a local variable

def fun():

num1 = 2

num2 = num1 + 1

print num2

fun()

# the scope of global num1 is the whole program, num1 remains defined

print num1

# the scope of the variable num2 is fun(), num2 is now undefined

#print num2

# why use local variable

# give a descriptive name to a quantity

# avoid computing something nultiple times

def fahren_to_kelvin(fahren):

celsius = 5.0/9 * (fahren -32)

zero_celsius_in_kelvin = 273.15

return celsius + zero_celsius_in_kelvin

print fahren_to_kelvin(32)

# the risk/reward of using global variable

# risk -consider the software system for an airliner

# critical piece - flight control system

# non-critical piece - in-flight entertainment system

# both systems might use a variable called "dial"

# we don't want possibility that change the volume on your autio

# cause the plane's flags to change!

# example

num = 4

def fun1():

global num

num = 5

def fun2():

global num

num = 6

# note that num changes after each call with no obvious explanation

print num

fun1()

print num

fun2()

print num

# global variables are an easy way for event handlers

# to communicates game information.

# safer method - but they required more sophisticated

# object-programming technique