python 学习(一) 字符串、函数
如果脚本中有中文，要在文件头加上如下内容：
# -*- coding: utf-8 -*-
指定默认路径
# /usr/local/python
字符串连接：
print "2+3=",5`
print "2+3="+str(5)`
a=2
b=3
c=5
print "%d+%d=%d"%(a,b,c)
%r与%s %r打印变量原始值，不对变量进行任何编解码，适合用于调试
如"hello\nworld" %r 打印hello\nworld
formatter = "%r %r %r %r"
print formatter % (1, 2, 3, 4)
print formatter % ("one", "two", "three", "four")
print formatter % (True, False, False, True)
转义列表
\\ Backslash (\)
\' Single-quote (')
\" Double-quote (")
\a ASCII bell (BEL)
\b ASCII backspace (BS)
\f ASCII formfeed (FF)
\n ASCII linefeed (LF)
\N{name} Character named name in the Unicode database (Unicode only)
\r Carriage Return (CR)
\t Horizontal Tab (TAB)
\uxxxx Character with 16-bit hex value xxxx (Unicode only)
\Uxxxxxxxx Character with 32-bit hex value xxxxxxxx (Unicode only)
\v ASCII vertical tab (VT)
\ooo Character with octal value ooo
\xhh Character with hex value hh
非unicode类型的字符串中“\uxxxx”不能直接打印。需要调用相应方法将其转换为unicode类型，如：
print '\u559c'.decode('unicode_escape')
定义为unicode类型即可
print u'\u559c'
字符串输入&类型转换：
print "How old are you?",
age = int(raw_input())
age = int(raw_input("How old are you?"))
字符串换行两种方式：
a="aaaaaaaaa"\
"bbbbbbbb"
a=("aaaaaaaaa"
"bbbbbbbbb")#推荐
与环境交互：
from sys import argv
script, first, second, third = argv
# argv[0]为脚本名
# or
import sys
script, first, second, third = sys.argv
# sys.argv[0]为脚本名
乘幂a=2**7 #a=128
使用r强制不转义
>>> print 'C:\some\name' # here \n means newline!
C:\some
ame
>>> print r'C:\some\name' # note the r before the quote
C:\some\name
创建Unicode字符串
a=u"Unicode"
关于字符串索引：
+---+---+---+---+---+---+
| P | y | t | h | o | n |
+---+---+---+---+---+---+
0 1 2 3 4 5
-6 -5 -4 -3 -2 -1
字符串相关方法
str="ssstttrrr"
len(str) #求长度
# unicode与8进制字符串相互转换
u"盲枚眉".encode('utf-8')
unicode('\xe7\x9b\xb2\xe6\x9e\x9a\xe7\x9c\x89', 'utf-8')
列表操作
squares = [1, 4, 9, 16, 25]
a = ['spam', 'eggs', 100, 1234]
>>> squares[0] # indexing returns the item
1
>>> squares[-1]
25
>>> squares[-3:] # slicing returns a new list
[9, 16, 25]
>>> squares + [36, 49, 64, 81, 100]
[1, 4, 9, 16, 25, 36, 49, 64, 81, 100]
>>> cubes.append(216) # add the cube of 6
>>> cubes.append(7 ** 3) # and the cube of 7
>>> cubes
[1, 8, 27, 64, 125, 216, 343]
函数定义
def ask_ok(prompt, retries=4, complaint='Yes or no, please!'):
ask_ok('Do you really want to quit?')
ask_ok('OK to overwrite the file?', 2)
ask_ok('OK to overwrite the file?', 2, 'Come on, only yes or no!')
def parrot(voltage, state='a stiff', action='voom', type='Norwegian Blue'):
parrot(1000) # 1 positional argument
parrot(voltage=1000) # 1 keyword argument
parrot(voltage=1000000, action='VOOOOOM') # 2 keyword arguments
parrot(action='VOOOOOM', voltage=1000000) # 2 keyword arguments
parrot('a million', 'bereft of life', 'jump') # 3 positional arguments
parrot('a thousand', state='pushing up the daisies') # 1 positional, 1 keyword
引入一个形如 **name 的参数时，它接收一个字典(参见 Mapping Types — dict )，该字典包含了所有未出现在形式参数列表中的关键字参数。这里可能还会组合使用一个形如 *name (下一小节详细介绍)的形式参数，它接收一个元组(下一节中会详细介绍)，包含了所有没有出现在形式参数列表中的参数值。( *name 必须在 **name 之前出现)
def cheeseshop(kind, *arguments, **keywords):
print "-- Do you have any", kind, "?"
print "-- I'm sorry, we're all out of", kind
for arg in arguments:
print arg
print "-" * 40
keys = sorted(keywords.keys())
for kw in keys:
print kw, ":", keywords[kw]
cheeseshop("Limburger", "It's very runny, sir.",
"It's really very, VERY runny, sir.",
shopkeeper='Michael Palin',
client="John Cleese",
sketch="Cheese Shop Sketch")
### 输出
-- Do you have any Limburger ?
-- I'm sorry, we're all out of Limburger
It's very runny, sir.
It's really very, VERY runny, sir.
----------------------------------------
client : John Cleese
shopkeeper : Michael Palin
sketch : Cheese Shop Sketch
另有一种相反的情况: 当你要传递的参数已经是一个列表，但要调用的函数却接受分开一个个的参数值。这时候你要把已有的列表拆开来。例如内建函数 range() 需要独立的 start ，stop 参数。 你可以在调用函数时加一个 * 操作符来自动把参数列表拆开:
>>> list(range(3, 6)) # normal call with separate arguments
[3, 4, 5]
>>> args = [3, 6]
>>> list(range(*args)) # call with arguments unpacked from a list
[3, 4, 5]
以同样的方式，可以使用 ** 操作符分拆关键字参数为字典:
>>> def parrot(voltage, state='a stiff', action='voom'):
... print "-- This parrot wouldn't", action,
... print "if you put", voltage, "volts through it.",
... print "E's", state, "!"
...
>>> d = {"voltage": "four million", "state": "bleedin' demised", "action": "VOOM"}
>>> parrot(**d)
-- This parrot wouldn't VOOM if you put four million volts through it. E's bleedin' demised !