python_note.txt

source (m.py) --> Byte code(m.pyc) --> Rutime (PVM)

Ctrl + D	to exit from python
quit()

Using the interactive Prompt
1. Type Python commands only
2. print statements are required only in files
3. Don't indent at the interactive prompt(yet)
4. Watch out for prompt changes and compound statements.

----------------------------------------------------------------------------------
#!/usr/bin/python
print 2 ** 8				# Raise to a power
print 'the bright side ' + 'of life'	# + means concatenation
----------------------------------------------------------------------------------

----------------------------------------------------------------------------------
#!/usr/bin/env python, but does env.
print 2 ** 8				# Raise to a power
print 'the bright side ' + 'of life'	# + means concatenation
----------------------------------------------------------------------------------

on Windows
----------------------------------------------------------------------------------
import sys
print sys.platform
print 2 ** 100
raw_input()				# added. prevent popup and exit.
----------------------------------------------------------------------------------

import a scipt will run it once.
if you want run it again, you can reload it.
----------------------------------------------------------------------------------
>>> import script4
hello world
>>> import script4
>>> import script4
>>> reload (scritp4)
hello world
----------------------------------------------------------------------------------

Module Attributes

myfile.py
---------------------------------------------------------------------------------
tile = "The Meaning of Life"
---------------------------------------------------------------------------------

Test.py
---------------------------------------------------------------------------------
import myfile
print myfile.title
---------------------------------------------------------------------------------
or
---------------------------------------------------------------------------------
from myfile import title
print title
---------------------------------------------------------------------------------

dir(myfile)			# built-in function to fetch a list of names available
['__builtins__', '__doc__', '__file__', '__name__', '__package__', 'a', 'b', 'c', 'title']

execfile()			# exec a file


Chapter 4  Introducing Python Object Types
==========================================
Numbers			1234, 3.1415, 999L, 3+4j, Decimal
Strings			'spam',"guido's"
Lists			[1, [2, 'three'], 4]
Dictionaries		{'food': 'spam', 'taste': 'yum'}
Tuples			(1,'spam', 4, 'U')
Files			myfile = open('eggs', 'r')
Other types		Sets, types, None, Booleans



Numbers:
	123+222
	1.5 * 4
	2 ** 100,000
	
	import math
	math.pi
	math.sqrt(65)

	import random
	random.random()
	random.choice([1,2,3,4])

Strings:
	S = 'Spam'
	len(S)
	S[0]
	S[1]
	S[-1]
	S[-2]
	S[len(S)-1]
	S[1:3]
	S[1:]
	S[:3]
	S[:]
	S + 'xyz'
	S * 8
	Immutability
		S[0]='z'	# ERROR!!!
		S='z'+S[1:]
	S.find('pa')
	S.replace('pa', 'XYZ')
	line='aaa,bbb,ccccc,dd'
	line.split(',')
		['aaa','bbb','ccccc','dd']
	S.upper()
		'SPAM'
	S.isalpha()
	line='aaa,bbb,ccccc,dd\n'
	line=line.rstrip()		# Remove whitespace charactors on the right side.

	dir(S)
		# Get the methods

	Pattern Matching
		import re
		match = re.match('Hello[ \t]]*(.*)world', 'Hello	Python world')
		match.group(1)
		match.groups()

List:
	L = [123, 'Spam', 1.23]
	len(L)
	L(0)
	L[:-1]
	L + [4, 5, 6]
	L
	L.append('NI')
	L.pop(2)	# Delete an item in the middle
	
	M = ['bb', 'aa', 'cc']
	M.sort()
	M.reverse()	# 反序

	M = [[1, 2, 3],
	     [4, 5, 6],
	     [7, 8, 9]]
	M[1][2]

	col2=[row[1] for row in M]
	[row[1] for row in M if row[1] % 2 ==0]
	diag=[M[i][i] for i in [0,1,2]]
	doubles=[c*2 for c in 'spam']

Dictionaries:
	D = {'food': 'Spam', 'Quantity': 4, 'color': 'pink'}
	D['quantity'] += 1

	D={}
	D['name'] = 'Bob'
	D['job'] = 'dev'
	D['age'] = 40
	D

	Nesting Revisited
		rec = {'name'" {'first': 'Bob', 'last': 'Smith'},
			'job': ['dev', 'mgr'],
			'age': 40.5}
		rec['job'].append('jnaitor')
		rec

		rec = 0		# Now the object's space is reclaimed.
				# Release the memory space

	D = {'a': 1, 'b': 2, 'c': 3}
	for key in sorted(D):
		print key, '=>', D[key]
	

	for c in 'spam':
		print c.upper()

	squares = [x ** 2 for x in [1, 2, 3, 4, 5]]
	squares

	squares = []
	for x in [1, 2, 3, 4, 5]:
		squares.append(x ** 2)

	Missing Keys: if Tests
		D.has_key('f')
		if not D.has_key('f'):
		    print 'missing'

Tuples:
	T = (1, 2, 3, 4)
	len(T)
	T + (5, 6)

	T[0] = 2		# ERROR!!!!!!!!!
				# Tuples are immutable


Files:
	f = open('data.txt', 'w')
	f.write('Hello\n')
	f.write('world\n')
	f.close()
	
	f.read()
	f.seek(0)
		# Always use help to find how to use it!

Other Core Types:
	Set:(集合)
		X = set('spam')
		Y = set(['h', 'a', 'm'])
		X, Y
			(set(['a', 'p', 's', 'm'), set(['a', 'h', 'm']))

		X & Y
		X | Y
		X - Y

	decimal num:
		import decimal
		d = decimal.Decimal('3.141')
		d + 1

	booleans:
		1 > 2, 1 < 2
		bool('spam')

	None:
		X = None
		print X
		L = [None] * 100
		L

	Type:
		type(L)
		type(type(L))

		if type(L) == type([]):
			print 'yes'

		if type(L) == list:
			print 'yes'

		if isinstance(L, list):
			print 'yes'



Immutability
Sequences
Polymorphism //多态