Python

links

http://en.wikibooks.org/wiki/Non-Programmer%27s_Tutorial_for_Python_2.6
http://docs.python.org/tutorial

Reference

http://docs.python.org/ref/ref.html

basics

print "Hello, World!"

command called print followed by one argument,which is "Hello, World!". (referred to as a string of characters, or string) Command and its arguments are collectively referred to as a statement,

print "2 + 2 is", 2 + 2

The first argument is the string "2 + 2 is" and the second argument is the mathematical expression 2 + 2, which is commonly referred to as an expression. each of the arguments separated by a comma

sys.argv   arguments are passed to the script in the variable sys.argv
#          is used to start a comment

operations for numbers

Operation	Symbol	Example
Power (exponentiation)	**	5 ** 2 == 25
Multiplication	*	2 * 3 == 6
Division	/	14 / 3 == 4
Remainder (modulo)	%	14 % 3 == 2
Addition	+	1 + 2 == 3
Subtraction	-	4 - 3 == 1

userinput

raw_input (returns a string)

user_reply = raw_input("Who goes there? ")

input (returns digits)

number = input("Type in a number: ")

type(number) (tells what a variable is.)

print "number is a", type(number)

while loop

print number interval. finish while loop with a ':' The while statement only affects the lines that are indented with whitespace.

start = input("Start number? ")
stop = input("Stop number? ")
a = start
while a < stop:
    print a
    a = a + 1

operator	function
<	less than
<=	less than or equal to
>	greater than
>=	greater than or equal to
==	equal
!=	not equal
<>	another way to say not equal (old style, not recommended)

if statment

 if a > 5:  
   print a, ">", 5
 elif a <= 7:
   print a, "<=", 7
 else:
   print "Neither test was true"

1. This Program Demonstrates the use of the == operator # using numbers

print 5 == 6 

false

functions

The key feature of this program is the def statement. def (short for define) starts a function definition. def is followed by the name of the function absolute_value. Next comes a '(' followed by the parameter n (n is passed from the program into the function when the function is called). The statements after the ':' are executed when the function is used. The statements continue until either the indented statements end or a return is encountered. The return statement returns a value back to the place where the function was called.

def absolute_value(n):
  if n < 0:
    n = -n
  return n