Python 基础参考

numbers = [1,2,3,4,5,6,7,8,9,10] #声明

numbers[3:6] #Slice 分片操作
#=> [4,5,6] 第二个索引号的元素不包含

numbers[-3:]
#=> [8,9,10]

numbers[0:10:2]
 #=> [1,3,5,7,9]

numbers[10:0:-2]
#=> [10,8,6,4,2]

[1,2,3] + [4,5,6]
#=> [1,2,3,4,5,6]

[42] *6
#=> [42,42,42,42,42,42]

#delete element
numbers[5] = 64
del numbers[5]
#分片插入元素
numbers[5:5] = [6,6]

#分片删除元素
numbers[2:8] = []

name = list('perl')
name[2:] = list('ar')
# name => ['p', 'e', 'a', 'r']

1,2,3 or (1,2,3)
#=> (1,2,3)
() #空元组
#=> ()
(1,) or 1,
#=> (1,)
3*(40+2,)
#=>(42,42,42)

tuple([1,2,3])
#=> (1,2,3)

format = "Hello, %s. %s enough for ya?"
values = ('world', 'Hot')
print format % values
#=>Hello, world. Hot enough for ya?

phonebook={'Alice': '2341', 'Beth': '9102', 'Cecil': '3258'}#直接创建
phonebook['Cecil']
#=> '3258'

phonebook={}
phonebook['Denver'] = '5345'
phonebook
#=> { 'Denver': '5345' }

items = [('name', 'Gumby'), ('age', 42)]
d = dict(items)
d
#=> {'age': 42, 'name': 'Gumby'}

d=dict(name='Gumby', age=42) #另一种声明

len(d)
del d[k]
k in d#(检查是否存在 k 键)

"Cecil's phone number is %(Cecil)s." % phonebook
#=>"Cecil's phone number is 3258."

set([0,1,2,3,0,1,2,3,4,5])#set 是由序列(或其他可迭代对象)构建的。
#=>set([0,1,2,3,4,5])#相同的成员会被忽略。
set(['fee', 'fie', 'foe'])
#=>set(['foe', 'fee', 'fie'])#与字典一样，顺序是未知的

from heapq import *
from random import shuffle
data=range(10)
shuffle(data)
heapify(data)
heappush(data, 0.4)
heap
#=>[0, 0.4, 4, 5, 1, 8, 9, 6, 7, 3, 2]
heappop(data)
#=>0

data=range(10)
shuffle(data)
nlargest(1, data)
#=>9
nsmallest(1,data)
#=>0

from collections import deque
q = deque(range(5))
q.append(5)#默认在队列右端追加
q.appendleft(6)
q
#=>deque([6,0,1,2,3,4,5])
q.pop()#默认从队伍右端 pop 出元素
#=>5
q.popleft()
#=>6
q.rotate(3)#右移三个元素
#=>deque([2,3,4,0,1])
q.rotate(-1)#左移一个元素
#=>deque([3,4,0,1,2])

x, y, z = 1, 2, 3

x, y = y, x

values = 1, 2, 3
values
#=> (1, 2, 3)
x, y, z = values
x
#=> 1

key, value = scoundrel.popitem()

a, b, rest* = [1, 2, 3, 4]
rest
#=> [3, 4]

x = y = somefunction()
#等同于
y = somefunction()
x = y
#不一定等价于
x = somefunction()
y = somefunction()

[x*x for x in range(10)]
#=> [0, 1, 4, 9, 25, 36, 49, 64, 81]

#可加条件：
[x*x for x in range(10) if x % 3 ==0]
#=>[0, 9, 36, 81]

[(x, y) for x in range(3) for y in range(3)]
#=>[(0, 0), (0, 1), (0, 2), (1, 0), (1, 1), (1, 2), (2, 0), (2, 1), (2, 2)]

#等同于
result = []
for x in range(3):
    for y in range(3):
result.append((x, y))

names = ['name1', 'name2']
ages = [12, 45]
zip(names, ages)
#=> [('name1', 12), ('name2', 45)]

#解包元组，遍历
for name, age in zip(names, ages):
    print name, 'is', age, 'years old'

for index, string in enumerate(strings):
    if 'xxx' in string:
    strings[index] = '[censored]'

list(reversed('Hello,World!'))
#=>'!dlroW,olleH'

for n in range(99, 81, -1):
    root = sqrt(n)
    if root == int(root):
	print n
	break
else:
    print "Didn't find it!"

def hello(greeting, name):
    print '%s, %s' % (greeting, name)

hello('Hello', 'world')#参数顺序难记时，使用 参数名=传入值 的形式
hello(greeting='Hello', name='world')

def hello2(greeting='Hello', name='world'): #提供默认值
    print '%s, %s!' % (greeting, name)
hello2()
#=>Hello, world!

#序列用法
def  add(x, y): return x + y
params = (1, 2)
add(*params)#加上*
#=>3

#字典用法
def hello3(greeting='Hello', name='world'):
    print '%s, %s!' % (greeting, name)
params = {'name': 'Sir Robin', 'greeting': 'Well met'}
hello3(**params)#加上**
#=>Well met, Sir Robin!

scope = vars()#vars()返回全局变量的字典
x=1
scope['x']
#=>1
scope['x'] += 1
x
#=>2

def power(x, n):
    if n == 0:
    return 1
    else:
    return x * power(x, n-1)

def foo():
    m=3
    n=5
    def bar():
	a=4
	return m+n+a
    return bar

>>>bar =  foo()
>>>bar()
12

import dis
code_obj = compile('sum([1,2,3])',  '', 'single')

>>>exec(code_obj)
6

>>> dis.dis(code_obj)
  1           0 LOAD_NAME                0 (sum)
	      3 LOAD_CONST               0 (1)
	      6 LOAD_CONST               1 (2)
	      9 LOAD_CONST               2 (3)
	     12 BUILD_LIST                   3
	     15 CALL_FUNCTION          1
	     18 PRINT_EXPR
	     19 LOAD_CONST               3 (None)
	     22 RETURN_VALUE

from functools import partial
def foo(a,b,c):
    return a+b+c

foo2 = partial(foo, b=2)
foo2(a=1, c=3)
#=>6

from functools import partial
bin2dec = partial(int, base=2)
hex2dec = partial(int, base=16)

int('15') #=>15  using default base 10
bin2dec('01011') #=>11
hex2dec('67') #=>103

def foo(a):
    def bar(b):
	return a+b
    return bar

fibs = [0, 1]
for i in range(8):
    fibs.append(fibs[-2] + fibs[-1])
fibs
#=> [0, 1, 1, 2, 3, 5, 8, 13, 21, 34]
#抽象成
fibs(num)

class A:
    def a(self):
	print 'Hello'

i = A()
i.a
#=><bound method A.a of <__main__.A instance at 0x01E26648>>
i.a()
#=>Hello
#等同于
A.a(i)
#=>Hello

class A:
    def a(self):
	print 'Hello'
def b():
    print 'World'

i=A()
i.a=b#i.a 是一个特性，可以绑定任何方法
i.a
#=><function b at 0x01E279B0>
i.a()
#=>World
A.a(i)
#=>Hello

i2=A()
c=i2.a#c 是方法变量
c
#=><bound method A.b of <__main__.A instance at 0x01E2F8A0>>
c()
#=>Hello

class Secretive:
    def __inaccessible(self):
	print "You can't find me"
    def accessible(self):
	print "You can find me"
	self.__inaccessible()
i=Secretive()
i.__inaccessible()
#=>Error
i.accessible()
#=>You can find me
#=>You can't find me

__metaclass__=type
class Retangle:
    def __init__(self):
	self.width=0
	self.height=0
    def setSize(self, size):
	self.width, self.height=size
    def getSize(self):
	return self.width, self.height
    size = property(getSize, setSize)

r = Retangle()
r.width=10
r.height=5
r.size
#=>(10, 5)
r.size = 150, 100
r.width
#=>150

class Retangle:
    def __setattr__(self, name, value):
	if name =='size':
	    self.width, self.height = value
	else:
	    self.__dict__[name] = value
    def __getattr__(self,name):
	if name == 'size':
	    return self.width, self.height
	else:
	    raise AttributeError

class Parent:
    def init(self):
	print "Init Parent done"

class ChildA(Parent):
    def init(self):#重写父类的 init 方法
	print "Init Child done"

class ChildB(Parent):
    pass

p = Parent()
p.init()
#=>Init Parent done
a = ChildA()
a.init()
#=>Init Chile done
b = ChildB()
b.init()
#=>Init Parent done

issubclass(ChildA, Parent)
#=>True

ChildA
#=><class __main__.ChildB at 0x01E44EA0>
ChildA.__bases__#查找父类
#=>(<class __main__.Parent at 0x01E1F340>,)

isinstance(a, ChildA)
#=>True
isinstance(a, Parent)
#=>True

a
#=><__main__.ChildA instance at 0x01E181C0>
a.__class__
#=><class __main__.ChildA at 0x01E32030>

class Drived(Base):
    def __init__(self):
	Base.__init__(self)#调用基类构造
	self.var1=5#自身特性赋值

class Drived(Base):
    def __init__(self):
	super(Drived, self).__init__()

class TestIterator:
    def __init__(self):
	self.value=0
    def next(self):
	self.value += 1
	if self.value > 10: raise StopIteration #没有这行，list 会无限循环下去
	return self.value
    def __iter__(self):
	return self
ti = TestIterator()
list(ti)
#=> [1,2,3,4,5,6,7,8,9,10]

def repeater(value):
    while True:
	new = (yield value)
	if new is not None: value = new

r = repeater(42)
r.next()
#=>42
r.send("hello world")#yield 语句后的变量被赋值为'hello world'
#=>'hello world'
r.next()
#=>'hello world'

def flatten(nested):
    result=[]
    try:
	for sublist in nested:
	    for element in flatten(sublist):
		result.append(element)#对应 yield element
    except TypeError:
	result.append(nested)
    return result

#state[0]=3 表示第一行第四列
def conflict(state, nextX):
    'state 是已放置好的皇后的位置信息，nextX 为新增皇后的行位置(对于空 state 也能正常运作)'
    nextY = len(state)
    for i in range(0, nextY):
	if abs(nextX-state[i]) in (0, nextY-i):
	    return True
    return False

def queens(n, state=()):
    for pos in range(n):
	if not conflict(state, pos):
	    if len(state) == n-1:#表示仅最后一个位置未放置皇后，递归的最终层
		yield (pos,)
	    else:
		for result in queens(n, state + (pos,)):#当最后一层 yield 出内容后，此处 result 才会有结果。
		    yield (pos,) + result

list(queens(4, (1,)))
#=>[(3,0,2)]
list(queens(4))
#=>[(1,3,0,2), (2,0,3,1)]

def prettyprint(state):
    def line(x, length):
	return '. '*x + 'X ' + '. '*(length-x-1)
    for x in state:
	print line(x, len(state))

import random
prettyprint(random.choice(list(queens(4))))
#=>
. X . .
. . . X
X . . .
. . X .

[n for n in dir(copy) if not n.startswith('_')]#此处用列表推导式过滤掉了系统用的__开头的函数
#=>['Error', 'PyStringMap', 'copy', 'deepcopy', 'dispatch_table', 'error', 'name', 't', 'weakref']

copy.__all__
#=>['Error', 'copy', 'deepcopy']

给 py 文件行末追加行号的例子：
#numberlines.py
import fileinput
for line in fileinput.input(inplace=True):
    line = line.rstrip()
    num = fileinput.lineno()
    print '%-50s # %2i' % (line, num)

python  numberlines.py numberlines.py

import shelve
s = shelve.open('D:\\test.dat')#创建简单 DB 文件
s['x'] = ['a', 'b', 'c']
#s['x'].append('d')无效

temp = s['x']
temp.append('d')
s['x'] = temp#必须给 s['x']特性重新赋值修改才能写入 DB 文件
s.close()

s = shelve.open('D:\\test.dat')
s
#=>{'x' : ['a', 'b', 'c', 'd']}

from ConfigParser import ConfigParser
CONFIGFILE = "testconfig.txt"
config = ConfigParser()
config.read(CONFIGFILE)
print config.get('messages', 'greeting')
print config.getfloat('numbers', 'pi') * (4**2)

import logging
logging.basicConfig(level=logging.INFO, filename='Mylog.log')
logging.info('Starting program')

f = open('test.txt', 'w')
f.write('Append text.')#重写文件内容
f.write('Append text2.')#追加内容
f.close

f = open('test.txt', 'r')#r 也可不加，默认是读取模式打开
f.read(4)
#=>'Appe'
f.read()
#=>'nd text.'
f.close()

# somescript.py
import sys
text = sys.stdin.read()
words = text.split()
wordcount = len(words)
print 'Wordcount:', wordcount

cat somefile.txt | python somescript.py
#=>Wordcount:3

with open("somefile.txt") as somefile:
    do_something(somefile)
#with 语句块结束时，关闭 somefile，等同于 finally 效果

f = open(filename)
while True:
    char = f.read(1)
    if not char: break
    process(char)
f.close()

f = open(filename)
while True:
    line = f.readline()
    if not line: break
    process(line)
f.close()

f = open(filename)
for char in f.read():
    process(char)
#or
for line in f.readlines():
    process(line)
f.close

import fileinput
for line in fileinput.input(filename):
    process(line)

f = open(filename)
for line in f:
    process(line)
f.close

for line in open(filename):
    process(line)

#socket server test
import socket
s = socket.socket()
host = socket.gethostname()
port =1234

s.bind((host, port))
s.listen(5)
while True:
    c, addr = s.accept()
    print 'Got connection from', addr
    c.send('Thank you for connectin')
    c.close()

#socket client test
import socket
s = socket.socket()
host = socket.gethostname()
port = 1234

s.connect((host, port))
print s.recv(1024)
s.close()

__DEBUG = True
def test():
    a = 5
    if __DEBUG:
	import pdb
	pdb.set_trace()
    b = 4
    print a + b

import profile
from my_math import product
profile.run('product(1, 2)')

import pstats
p = pstats.Stats('my_math.profile')