CS 696 Lecture 3: Introduction to Grid Computing - Control Statements and Functions, Study notes of Computer Science

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CS 696 - Introduction to Grid Computing:

Lecture

Mary Thomas

San Diego State

Thursday, 25-Jan-

Basics

 Mailing List: please sign up

 http://scilists.sdsu.edu/mailman/listinfo.cgi/cs696-grid

 References:

 Python Tutorial & Docs, Guido van Rossum,

 http://www.python.org/doc/current/tut/tut.html

 Learning Python, Lutz & Ascher, O'Reilly, 1999

 Web Programming in Python, by Thiruvathukal, et

al.

 Out of print, but we will get electronic copy soon.

Control Statements

if while for Basic Structure

HeaderLine:

block

Block are indicated by indentation Space Tab Indentation always indicates a block Following does not compile print "Good Start" print "This is a compile error"

Importing modules (quick lesson)

#Fibonacci numbers module

#return Fiboacci series up to n

def fib(n):

a, b = 0, 1

while b < n :

print b,

a, b = b, a+b

def fib2(n):

result = []

Print ‘fib2’

a, b = 0, 1

while b < n :

result.append(b)

a, b = b, a+b

return result

>>> import fibo

>>> fibo.fin(20)

>>> fibo.fib2(50)

[1, 1, 2, 3, 5, 8, 13, 21, 34]

# edit changes fibo.py

>>>reload(fibo)

>>> fibo.fib2(50)

fib

[1, 1, 2, 3, 5, 8, 13, 21, 34]

[gidget:% chmod 755 fibo.py

[gidget:% ls fibo.py

-rwxr-xr-x … fibo.py

while

while : else: #optional else is run if didn't exit from loop with a break Example

>>> x='cat'

>>> while x:

... print x

... x=x[1:]

... else:

... print 'else'

... print 'the end'

cat

at

t

else

the end

break, continue, pass

break Jump out of closest enclosing loop continue Jump to top of the closest enclosing loop pass Does nothing, empty statement

while x<5: ... x=x+ ... print x ...

1 2 3 4 5

while x<5: ... x=x+ ... if x == 3: ... break ... print x ... x= while x<5: ... x=x+ ... if x == 3: ... break ... print x ... 1 2

Range

range(5) [0, 1, 2, 3, 4] range(5, 10) [5, 6, 7, 8, 9] range(5, 10, 3) [5, 8] for k in range(10): print k, #prints 1 2 3 4 5 6 7 8 9 for k in range(1, 20, 2): print k #prints odd number < than 20 list = ['cat', 'rat', 'bat']

for k in range(len(list)): print k, list[k], range(upto) range(start, upto) range(start, upto, increment)

A list with successive integers

Functions

def fibonacci(n): result = [] a, b = 0, 1 while b < n: result.append(b) a,b = b,a+b return result def doesNothing(): pass print fibonacci(20) print doesNothing() Output [1, 1, 2, 3, 5, 8, 13] None Can define default arg values def f(a=5): or use key-value pairs Def f( action=‘go’ )

Scope of Names

What does this print? x = 10 def whichValue(x): print x whichValue(5)

Local Variables to a Function

Each call to a function creates a new local scope Arguments to the function are local Assigned names are local, unless declared global x = 10 def printGlobal(): print x printGlobal() # prints 10 x = 5 printGlobal() # prints 5 x = 10 def printLocal(): x = 5 #Makes a local x print x

>>> printGlobal()

>>> printLocal()

>>> printGlobal()

Global Declaration Example

x = 10 def globalDeclaration(): global x x = 5 globalDeclaration() print x # prints 5 Seems like something to avoid

Recursive Functions

def factorial(x): if x == 1: return 1 else: return x * factorial(x - 1) print factorial(4)

Default Parameter Values

def defaultValues(x, y=10): return x + y defaultValues(2,3) #returns 5 defaultValues(2) #returns 12 ouch = 1 def tricky(x = ouch ): print x tricky() ouch = 2 tricky() Output 1 1

Positional Parameter Passing

def concat(x, y, z): return x + y + z concat('a', 'b', 'c') #'abc’ concat('a', z='b', y='c') #'acb’ concat('a', y='c',z='b') #'acb’ concat(y='a', x='c',z='b') #'cab'