Basic python

2013-01-27 | 分类 learning | 标签 python

python’s 29 keywords

and      def    exec    if     not   return
 assert   del    finally import or    try
 break    elif   for     in     pass  while
 class    else   from    is     print yield
 continue except global  lambda raise

Use module

Before we can use the functions from a module, we have to import them.To call one of the functions, we have to specify the name of the module and the name of the function, separated by a dot.module.func.

Fibonacci

previous = {0:1, 1:1}
def fibonacci(n):
	if previous.has_key(n):
		return previous[n]
	else:
		newValue = fibonacci(n-1) + fibonacci(n-2)
		previous[n] = newValue
		return newValue

To signal an exception using the `raise` statement.

def inputNumber () :
    x = input (’Pick a number: ’)
    if x == 17 :
        raise ValueError, ’17 is a bad number’
    return x

`str`

Printing a Point object implicitly invokes __str__ on the object, so defining __str__ also changes the behavior of print.

Python Data Structures

### Stack

class Stack:
	def __init__(self):
		self.items = []

	def push(self, item):
		self.items.append(item)

	def pop(self):
		return self.items.pop()

	def isEmpty(self):
		return (self.items == [])

Postfix example with statck.

def evalPostfix(expr):
  	import re
  	tokenList = re.split("([^0-9])", expr)
  	stack = Stack()
  	for token in tokenList:
    	if token == ’’ or token == ’ ’:
      		continue
    	if token == ’+’:
      		sum = stack.pop() + stack.pop()
      		stack.push(sum)
    	elif token == ’*’:
      		product = stack.pop() * stack.pop()
      		stack.push(product)
    	else:
      		stack.push(int(token))
  	return stack.pop()

Recommendations for further readings

Core Python Programming
Python Essential Reference
Python Pocket Reference

Recommended general computer science books

The Practice of Programming
The Open Book Project
The New Turing Omnibus
Turtles, Termites and Traffic
Programming Pearls