Python 学习笔记

合法的变量名,如: __my_name, name_23, a1b2_c3 等

and def exec if not returnassert del finally import or trybreak elif for in pass whileclass else from is print yieldcontinue except global lambda raise

>>> type(17)<type 'int'>

>>> type(3.2)<type 'float'>

>>> type(1L)<type 'long'>

>>> type(long(1))<type 'long'>

True 和 False,注意大小写

>>> type(True)<type 'bool'>

>>> type(1>2)<type 'bool'>

>>> type("Hello, World!")<type 'str'>

>>> type("WorldHello"[0])<type 'str'>

>>> type(['a','b','c'])<type 'list'>

>>> type([])<type 'list'>

>>> type(('a','b','c'))<type 'tuple'>

>>> type(())<type 'tuple'>

>>> type({'color1':'red','color12':'blue'})<type 'dict'>

>>> type({})<type 'dict'>

三引号:''' 或者 """ 是 python 的发明。三引号可以包含跨行文字,其中的引号不必转义。(即内容可以包含的换行符和引号)

如

注意,单引号和双引号没有任何不同,不像 PHP, PERL

例如: r"Newlines are indicated by \n."

在处理常规表达式,尽量使用 Raw String,免得增加反斜线。例如 r'1円' 相当于 '\1円'。

例如: u"This is a Unicode string."

例如 ur"\u0062\n" 包含三个字符

'What\'s ' "your name?" 自动转换为 "What's your name?" .

作用一:减少 \ 作为续行符的使用。

作用二:可以为每段文字添加注释。如:

用括号包含多行字串

header1 = "Dear %s," % name

header2 = "Dear %(title)s %(name)s," % vars()

String slices

len : 字符串长度

字符串比较

string 模组

# 错误!字符串不可更改greeting = "Hello, world!"greeting[0] = 'J' # ERROR!print greeting

longinteger ::= integer ("l" | "L")integer ::= decimalinteger | octinteger | hexintegerdecimalinteger ::= nonzerodigit digit* | "0"octinteger ::= "0" octdigit+hexinteger ::= "0" ("x" | "X") hexdigit+nonzerodigit ::= "1"..."9"octdigit ::= "0"..."7"hexdigit ::= digit | "a"..."f" | "A"..."F"

#!/usr/bin/pythondef func1(): print "func1: local x is", xdef func2(): x = 2 print 'func2: local x is', xdef func3(): global x print "func3: before change, x is", x x = 2 print 'func3: changed x to', xx = 1print 'Global x is', xfunc1()print 'Global x is', xfunc2()print 'Global x is', xfunc3()print 'Global x is', x

locals() 返回局部变量的 copy,不能修改

globals() 返回全局变量的 namespace, 可以通过其修改全局变量本身

[10, 20, 30, 40]

["spam", "bungee", "swallow"]

["hello", 2.0, 5, [10, 20]]

>>> range(1,5)[1, 2, 3, 4]

>>> range(10)[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

>>> range(1, 10, 2)[1, 3, 5, 7, 9]

类似数组下标

print numbers[0]

numbers[1] = 5

vocabulary = ["ameliorate", "castigate", "defenestrate"]numbers = [17, 123]empty = []print vocabulary, numbers, empty['ameliorate', 'castigate', 'defenestrate'] [17, 123] []

列表长度

+ (相加)

* (重复)

List slices

列表是变量,可以更改

列表中增加元素

删除列表中元素

查看列表的id

b = a,则两个变量指向同一个对象,两个变量的值一起变动

b = a[:],则建立克隆,b 和 a 指向不同对象,互不相干

list 作为函数的参数,是引用调用,即函数对 list 所做的修改会影响 list 对象本身

嵌套

矩阵

string.split 方法

string.join 方法

在最外面用圆括号括起来

必需是逗号分隔的多个值

Tuple 和 list 的区别就是: Tuple 是不可更改的,而 list 是可以更改的

一个元素也可以构成 list,但 tuple 必需为多个元素

Perl 管这种类型叫做 哈希表 或者关联数组。即下标可以是字符串的数组

>>> eng2sp = {}>>> eng2sp['one'] = 'uno'>>> eng2sp['two'] = 'dos'>>> print eng2sp{'one': 'uno', 'two': 'dos'}

>>> print eng2sp{'one': 'uno', 'three': 'tres', 'two': 'dos'}>>> print eng2sp['two']'dos'

keys() 方法,返回 keys 组成的列表

values() 方法,返回由 values 组成的列表

items() 方法,返回由 key-value tuple 组成的列表

haskey() 方法,返回布尔值

get() 方法

哈希表的克隆:copy() 方法

取反。 ~x 相当于 -(x+1)

temp=aa=bb=temp

#!/usr/bin/python# Filename : if.pynumber = 23guess = int(raw_input('Enter an integer : '))if guess == number: print 'Congratulations, you guessed it.' # new block starts here print "(but you don't win any prizes!)" # new block ends hereelif guess < number: print 'No, it is a little higher than that.' # another block # You can do whatever you want in a block ...else: print 'No, it is a little lower than that.' # you must have guess > number to reach hereprint 'Done'# This last statement is always executed, after the if statement# is executed.

#!/usr/bin/python# Filename : while.pynumber = 23stop = Falsewhile not stop: guess = int(raw_input('Enter an integer : ')) if guess == number: print 'Congratulations, you guessed it.' stop = True # This causes the while loop to stop elif guess < number: print 'No, it is a little higher than that.' else: # you must have guess > number to reach here print 'No, it is a little lower than that.'else: print 'The while loop is over.' print 'I can do whatever I want here.'print 'Done.'

break 语句跳出循环,且不执行 else 语句

#!/usr/bin/python# Filename : for.pyfor i in range(1, 5): print ielse: print 'The for loop is over.'

break 语句跳出循环,且不执行 else 语句

[ name for name in wikiaction.__dict__ ]

actions = [name[3:] for name in wikiaction.__dict__ if name.startswith('do_')]

字符串中的字符

函数名

括号和参数

冒号

#!/usr/bin/python# Filename : func_param.pydef printMax(a, b): if a > b: print a, 'is maximum' else: print b, 'is maximum'printMax(3, 4) # Directly give literal values

#!/usr/bin/python# Filename : func_default.pydef say(s, times = 1): print s * timessay('Hello')say('World', 5)

#!/usr/bin/python# Filename : func_key.pydef func(a, b=5, c=10): print 'a is', a, 'and b is', b, 'and c is', cfunc(3, 7)func(25, c=24)func(c=50, a=100)

#!/usr/bin/pythondef sum(*args): '''Return the sum the number of args.''' total = 0 for i in range(0, len(args)): total += args[i] return totalprint sum(10, 20, 30, 40, 50)

函数内部的第一行开始的字符串为 DocStrings

DocStrings 一般为多行

DocStrings 的存在证明了函数也是对象

help( ) 查看帮助就是调用函数的 DocStrings

abs(number) : 绝对值

cmp(x,y) : 比较x y 的值。返回 1,0,-1

divmod(x, y) -> (div, mod) : 显示除数和余数

pow(x, y[, z]) -> number

round(number[, ndigits]) -> floating point number : 四舍五入,保留 n 位小数

sum(sequence, start=0) -> value : 取 sequence 的和

hex(number) -> string : 返回十六进制

oct(number) -> string : 八进制

len(object) -> integer

max(sequence) -> value

min(sequence) -> value

range([start,] stop[, step]) -> list of integers

filter(function or None, sequence) -> list, tuple, or string

map(function, sequence[, sequence, ...]) -> list

reduce(function, sequence[, initial]) -> value

sorted(iterable, cmp=None, key=None, reverse=False) : 排序

zip(seq1 [, seq2 [...]]) -> [(seq1[0], seq2[0] ...), (...)]

coerce(x, y) -> (x1, y1)

chr(i) : 0<=i<256, 返回 ascii 码为 i 的字符

unichr(i) -> Unicode character : 返回 unicode 。 0 <= i <= 0x10ffff

ord(c) : 返回字符 c 的 ascii 码

delattr(object,name) : 在对象 object 中删除属性 name

getattr(object, name[, default]) -> value

hasattr(object, name) -> bool

id(object) -> integer : 返回对象 ID,相当于内存中地址

hash(object) -> integer : 两个对象具有相同的值,就有相当的 hash。但反之未必。

setattr(object, name, value) : 相当于赋值 x.y = v

isinstance(object, class-or-type-or-tuple) -> bool

issubclass(C, B) -> bool

globals() -> dictionary

locals() -> dictionary

vars([object]) -> dictionary

dir([object]) : 显示对象属性列表

repr(object) -> string : 对象 object 的正式名称

reload(module) -> module : 重新加载 module

iter

input([prompt]) -> value : 输入。相当于 eval(raw_input(prompt))。

raw_input([prompt]) -> string : 输入内容不做处理,作为字符串

__import__(name, globals, locals, fromlist) -> module : 动态加载模块

callable(object) : 是否可调用,如函数。对象也可以调用。

compile(source, filename, mode[, flags[, dont_inherit]]) -> code object

eval(source[, globals[, locals]]) -> value

execfile(filename[, globals[, locals]])

intern(string) -> string

str

unicode

bool

name = raw_input ("What...is your name? ")

age = input ("How old are you? ")

如果输入的不是数字,直接报错退出!

读

写

>>> f.write("Now is the time")>>> f.write("to close the file")

读取全部数据

读取定长数据

判断是否到文件尾:读取内容为空

>>> f.close()

def copyFile(oldFile, newFile):f1 = open(oldFile, "r")f2 = open(newFile, "w")while True: text = f1.read(50) if text == "": break f2.write(text)f1.close()f2.close()return

>>> cars = 52>>> "In July we sold %d cars." % cars'In July we sold 52 cars.'

>>> "In %d days we made %f million %s." % (34,6.1,'dollars')'In 34 days we made 6.100000 million dollars.'

>>> import pickle>>> f = open("test.pck","w")>>> pickle.dump(12.3, f)>>> pickle.dump([1,2,3], f)>>> f.close()>>> f = open("test.pck","r")>>> x = pickle.load(f)>>> x12.3>>> type(x)<type 'float'>>>> y = pickle.load(f)>>> y[1, 2, 3]>>> type(y)<type 'list'>

cPickle 是用 C 语言实现的,速度更快

比较两者时间

#!/usr/bin/python# Filename: pickling.pyimport cPickleshoplistfile = 'shoplist.data' # The name of the file we will useshoplist = ['apple', 'mango', 'carrot']# Write to the storagef = file(shoplistfile, 'w')cPickle.dump(shoplist, f) # dump the data to the filef.close()del shoplist # Remove shoplist# Read back from storagef = file(shoplistfile)storedlist = cPickle.load(f)print storedlist

Jiang Xin

class 是用 class 关键字创建的一个新类型

object 是该 class 的一个实例

class 中定义的变量称为 field

class 中定义的函数称为 method

instance variables

class variables

在 method 声明时必须提供,但是调用时又不能提供该参数

这个参数指向对象本身,一般命名为 self

python 在调用时会自动提供该参数

类 Person, 每新增一人,类变量 population 加一

代码

在对象建立时,该函数自动执行。

在用 del 删除对象时,该函数自动执行。

重载 <

重载 [key]

重载 len() 函数

当 print object 时,打印的内容

支持 iterator, 返回一个包含 next() 方法的对象。或者如果类定义了 next(), __iter__ 可以直接返回 self

# Filename: inheritance.pyclass SchoolMember: '''Represents any school member.''' def __init__(self, name, age): self.name = name self.age = age print '(Initialized SchoolMember: %s)' % self.name def tell(self): print 'Name:"%s" Age:"%s" ' % (self.name, self.age),class Teacher(SchoolMember): '''Represents a teacher.''' def __init__(self, name, age, salary): SchoolMember.__init__(self, name, age) self.salary = salary print '(Initialized Teacher: %s)' % self.name def tell(self): SchoolMember.tell(self) print 'Salary:"%d"' % self.salaryclass Student(SchoolMember): '''Represents a student.''' def __init__(self, name, age, marks): SchoolMember.__init__(self, name, age) self.marks = marks print '(Initialized Student: %s)' % self.name def tell(self): SchoolMember.tell(self) print 'Marks:"%d"' % self.markst = Teacher('Mrs. Abraham', 40, 30000)s = Student('Swaroop', 21, 75)print # prints a blank linemembers = [t, s]for member in members: member.tell() # Works for instances of Student as well as Teacher

#!/usr/bin/python# Filename: try_except.pyimport systry: s = raw_input('Enter something --> ')except EOFError: print '\nWhy did you do an EOF on me?' sys.exit() # Exit the programexcept: print '\nSome error/exception occurred.' # Here, we are not exiting the programprint 'Done'

#!/usr/bin/python# Filename: raising.pyclass ShortInputException(Exception): '''A user-defined exception class.''' def __init__(self, length, atleast): self.length = length self.atleast = atleast

try: s = raw_input('Enter something --> ') if len(s) < 3: raise ShortInputException(len(s), 3) # Other work can go as usual here.except EOFError: print '\nWhy did you do an EOF on me?'except ShortInputException, x: print '\nThe input was of length %d, it should be at least %d'\ % (x.length, x.atleast)else: print 'No exception was raised.'

# -*- python -*-version=0.1.a

a.py 与 b.py 在同一目录下

直接 import

使用 from module import 语法

将 a.py 拷贝到目录 dir_a 中

修改 sys.path, 将 dir_a 包含其中

将 dir_a 作为 package

import sysprint sys.path

#!/usr/bin/python# Filename: using_name.pyif __name__ == '__main__': print 'This program is being run by itself'else: print 'I am being imported from another module'

__init__.py 可以为空

__init__.py 可以包含 __all__变量

已如对于上例,在 __init__.py 中定义__all__ = ["a"]即当 from dir_a import * 的时候,import 的模组是 __all__ 中定义的模组

>>> import sys>>> sys.version'2.4.1 (#1, May 27 2005, 18:02:40) \n[GCC 3.3.3 (cygwin special)]'>>> sys.version_info(2, 4, 1, 'final', 0)>>> sys.platform, sys.maxint('linux2', 9223372036854775807)

显示 python 查询路径: sys.path

设置 Python 模组包含路径: sys.path.append( '/home/user')

>>> try:... raise IndexError... except:... print sys.exc_info()

try: raise TypeError, "Bad Thing"except: print sys.exc_info() print sys.exc_type, sys.exc_value

命令行参数数目: len(sys.argv) , 包含程序本身名称

sys.argv[0] 为程序名称, sys.argv[1] 为第一个参数,依此类推

示例1

示例2

>>> os.path.split('/home/swaroop/poem.txt')('/home/swaroop', 'poem.txt')

os.path.dirname('/etc/init.d/apachectl')

os.path.basename('/etc/init.d/apachectl')

os.popen('ls /etc').read()

os.popen('ls /etc').readlines()

import stringfruit = "banana"index = string.find(fruit, "a")print index

import mathx = math.cos(angle + math.pi/2)x = math.exp(math.log(10.0))

常规表达式。参考: http://docs.python.org/lib/module-re.html User Link

>>> help('sre')

^, $ 指代 字符串开始,结束。对于 re.MULTILINE 模式,^,$ 除了指代字符串开始和结尾,还指代一行的开始和结束

[ ] 字符列表,其中的 ^ 含义为"非"

*, +, ?, {m,n} : 量词(默认贪婪模式,尽量多的匹配)

*?, +?, ?? : 避免贪婪模式的量词

{m,n}? : 同样尽量少的匹配(非贪婪模式)

[(] [)]

( ) : 组合表达式,可以在后面匹配

(?iLmsux)

(?P<name>pattern) : 用名称指代匹配

(?P=name) : 指代前面发现的命名匹配

(?#...) : 为注释

(?:pattern)

(?=pattern) 正向前断言

(?!pattern) 负向前断言

(?<=pattern) 正向后断言

(?<!pattern) 负向后断言

\A Matches only at the start of the string.

\b Matches the empty string, but only at the beginning or end of a word

\B Matches the empty string, but only when it is not at the beginning or end of a word.

\d When the UNICODE flag is not specified, matches any decimal digit; this is equivalent to the set [0-9]. With UNICODE, it will match whatever is classified as a digit in the Unicode character properties database.

\D When the UNICODE flag is not specified, matches any non-digit character; this is equivalent to the set [^0-9]. With UNICODE, it will match anything other than character marked as digits in the Unicode character properties database.

\s When the LOCALE and UNICODE flags are not specified, matches any whitespace character; this is equivalent to the set [ \t\n\r\f\v]. With LOCALE, it will match this set plus whatever characters are defined as space for the current locale. If UNICODE is set, this will match the characters [ \t\n\r\f\v] plus whatever is classified as space in the Unicode character properties database.

\S When the LOCALE and UNICODE flags are not specified, matches any non-whitespace character; this is equivalent to the set [^ \t\n\r\f\v] With LOCALE, it will match any character not in this set, and not defined as space in the current locale. If UNICODE is set, this will match anything other than [ \t\n\r\f\v] and characters marked as space in the Unicode character properties database.

\w When the LOCALE and UNICODE flags are not specified, matches any alphanumeric character and the underscore; this is equivalent to the set [a-zA-Z0-9_]. With LOCALE, it will match the set [0-9_] plus whatever characters are defined as alphanumeric for the current locale. If UNICODE is set, this will match the characters [0-9_] plus whatever is classified as alphanumeric in the Unicode character properties database.

\W When the LOCALE and UNICODE flags are not specified, matches any non-alphanumeric character; this is equivalent to the set [^a-zA-Z0-9_]. With LOCALE, it will match any character not in the set [0-9_], and not defined as alphanumeric for the current locale. If UNICODE is set, this will match anything other than [0-9_] and characters marked as alphanumeric in the Unicode character properties database.

\Z Matches only at the end of the string.

re.I, re.IGNORE : 忽略大小写

re.L, re.LOCALE : \w, \W, \b, \B, \s and \S 参考当前 locale

re.M, re.MULTILINE : 将字符串视为多行,^ 和 $ 匹配字符串中的换行符。缺省只匹配字符串开始和结束。

re.S, re.DOTALL : . 匹配任意字符包括换行符。缺省匹配除了换行符外的字符

re.U, re.UNICODE : \w, \W, \b, \B, \d, \D, \s and \S 参考 Unicode 属性

re.X, re.VERBOSE : 可以添加 # 注释,以增强表达式可读性。

re.match( pattern, string[, flags]) 仅在字符串开头匹配。 相当于在 pattern 前加上了一个'^'!

re.search( pattern, string[, flags]) 在整个字符串中查询

使用 re.compile,对于需要重复使用的表达式,更有效率

prog = re.compile(pat)result = prog.match(str)相当于result = re.match(pat, str)

>>> re.split('\W+', 'Words, words, words.')['Words', 'words', 'words', '']>>> re.split('(\W+)', 'Words, words, words.')['Words', ', ', 'words', ', ', 'words', '.', '']>>> re.split('\W+', 'Words, words, words.', 1)['Words', 'words, words.']

查询所有匹配,返回 list

>>> p = re.compile('\d+')>>> p.findall('12 drummers drumming, 11 pipers piping, 10 lords a-leaping')['12', '11', '10']

查询所有匹配,返回 iterator

>>> p = re.compile('\d+')>>> iterator = p.finditer('12 drummers drumming, 11 ... 10 ...')>>> iterator<callable-iterator object at 0x401833ac>>>> for match in iterator:... print match.span()...(0, 2)(22, 24)(29, 31)

>>> re.sub ( 'id:\s*(?P<id>\d+)', 'N:\1円', 'userlist\nid:001,user001:jiangxin\nid:002,user003:tom\nid:003,user003:jerry\n')'userlist\nN:001,user001:jiangxin\nN:002,user003:tom\nN:003,user003:jerry\n'>>> re.sub ( 'id:\s*(?P<id>\d+)', r'N:1円', 'userlist\nid:001,user001:jiangxin\nid:002,user003:tom\nid:003,user003:jerry\n')'userlist\nN:001,user001:jiangxin\nN:002,user003:tom\nN:003,user003:jerry\n'

>>> re.sub ( 'id:\s*(?P<id>\d+)', r'N:\g<id>', 'userlist\nid:001,user001:jiangxin\nid:002,user003:tom\nid:003,user003:jerry\n')'userlist\nN:001,user001:jiangxin\nN:002,user003:tom\nN:003,user003:jerry\n'

返回值为: a tuple (new_string, number_of_subs_made).

re.compile 返回 的 compile 对象 的方法都有 re 类似方法对应,只是参数不同

re 相关对象有 flags 参数,而 compile 对象因为在建立之初已经提供了 flags,在 compile 相应方法中,用 pos, endpos 即开始位置和结束位置参数取代 flags 参数

match( string[, pos[, endpos]])

search( string[, pos[, endpos]])

split( string[, maxsplit = 0])

findall( string[, pos[, endpos]])

finditer( string[, pos[, endpos]])

sub( repl, string[, count = 0])

subn( repl, string[, count = 0])

expand( template)

group( [group1, ...])

groups( [default])

groupdict( [default])

start( [group]) 和 end( [group])

span( [group])

args 是除了应用程序名称外的参数,相当于: sys.argv[1:]

options 是短格式的参数支持。如果带有赋值的参数后面加上冒号":"。参见 Unix getopt()

long_options 是长格式的参数支持。如果是带有赋值的参数,参数后面加上等号"="。

返回值: 返回两个元素

>>> import getopt>>> args = '-a -b -cfoo -d bar a1 a2'.split()>>> args['-a', '-b', '-cfoo', '-d', 'bar', 'a1', 'a2']>>> optlist, args = getopt.getopt(args, 'abc:d:')>>> optlist[('-a', ''), ('-b', ''), ('-c', 'foo'), ('-d', 'bar')]>>> args['a1', 'a2']

"""Module docstring.This serves as a long usage message."""import sysimport getoptdef main(): # parse command line options try: opts, args = getopt.getopt(sys.argv[1:], "hp:", ["help", "port="]) except getopt.error, msg: print msg print "for help use --help" sys.exit(2) # process options for o, a in opts: if o in ("-h", "--help"): print __doc__ sys.exit(0) elif o in ("-p", "--port"): print "port is %d" % a # process arguments for arg in args: process(arg) # process() is defined elsewhereif __name__ == "__main__": main()

Level Numeric valueCRITICAL 50ERROR 40WARNING 30INFO 20DEBUG 10NOTSET 0

缺省为 root logger, 通过 getLogger 设置新的 logger 和名称

logging.basicConfig() logging.getLogger("").setLevel(logging.DEBUG) ERR = logging.getLogger("ERR") ERR = logging.getLogger("ERR") ERR.setLevel(logging.ERROR) #These should log logging.log(logging.CRITICAL, nextmessage()) logging.debug(nextmessage()) ERR.log(logging.CRITICAL, nextmessage()) ERR.error(nextmessage()) #These should not log ERR.debug(nextmessage())

logging.basicConfig(level=logging.DEBUG, format="%(levelname)s : %(asctime)-15s > %(message)s")

'''PROGRAM INTRODUCTIONUsage: %(PROGRAM)s [options]Options: -h|--help Print this message and exit.'''

def usage(code, msg=''): if code: fd = sys.stderr else: fd = sys.stdout print >> fd, _(__doc__) if msg: print >> fd, msg sys.exit(code)

说明: code 是返回值,msg 是附加的错误消息

#!/usr/bin/python# -*- coding: utf-8 -*-import sysimport getoptdef main(argv=None): if argv is None: argv = sys.argv try: opts, args = getopt.getopt( argv[1:], "hn:", ["help", "name="]) except getopt.error, msg: return usage(1, msg) for opt, arg in opts: if opt in ('-h', '--help'): return usage(0) #elif opt in ('--more_options'):if __name__ == "__main__": sys.exit(main())

利用 __name__ 属性,封装代码

sys.argv 参见

之所以为 main 添加缺省参数,是为了可以在交互模式调用 main 来传参

为防止 main 中调用 sys.exit(),导致交互模式退出,在 main 中使用 return 语句,而非 sys.exit

# 因为当前 locale 是 utf-8 编码,因此字符串默认编码为 utf-8>>> '中文''\xe4\xb8\xad\xe6\x96\x87'>>> isinstance('中文', unicode)False>>> isinstance('中文', str)True

# decode 是将 str 转换为 unicode>>> '中文'.decode('utf-8')u'\u4e2d\u6587'>>> isinstance('中文'.decode('utf-8'), unicode)True>>> isinstance('中文'.decode('utf-8'), str)False

# 前缀 u 定义 unicode 字串>>> u'中文'u'\u4e2d\u6587'>>> isinstance(u'中文', unicode)True>>> isinstance(u'中文', str)False

# encode 将 unicode 转换为 str>>> u'中文'.encode('utf-8')'\xe4\xb8\xad\xe6\x96\x87'>>> isinstance(u'中文'.encode('utf-8'), unicode)False>>> isinstance(u'中文'.encode('utf-8'), str)True

>>> len(u'中文')2>>> len(u'中文'.encode('utf-8'))6>>> len(u'中文'.encode('utf-8').decode('utf-8'))2

>>> "str1: %s, str2: %s" % ('中文', u'中文')Traceback (most recent call last): File "<stdin>", line 1, in ?UnicodeDecodeError: 'ascii' codec can't decode byte 0xe4 in position 6: ordinal not in range(128)

解决方案

mystr = '中文'mystr.encode('gb18030') 报错:Traceback (most recent call last): File "<stdin>", line 1, in ?UnicodeDecodeError: 'ascii' codec can't decode byte 0xe4 in position 0: ordinal not in range(128)

错误解析:mystr.encode('gb18030') 这句代码将 mystr 重新编码为 gb18030 的格式,即进行 unicode -> str 的转换。因为 mystr 本身就是 str 类型的,因此 Python 会自动的先将 mystr 解码为 unicode ,然后再编码成 gb18030。因为解码是python自动进行的,我们没有指明解码方式,python 就会使用 sys.defaultencoding 指明的方式来解码。很多情况下 sys.defaultencoding 是 ANSCII,如果 mystr 不是这个类型就会出错。拿上面的情况来说,缺省 sys.defaultencoding 是 anscii,而 mystr 的编码方式和文件的编码方式一致,是 utf8 的,所以出错了。

#! /usr/bin/env python# -*- coding: utf-8 -*-import sysreload(sys) # Python2.5 初始化后会删除 sys.setdefaultencoding 这个方法,我们需要重新载入sys.setdefaultencoding('utf-8')mystr = '中文'# 缺省先用定义的缺省字符集将 str 解码为 unicode,# 之后编码为 gb18030mystr.encode('gb18030')

#! /usr/bin/env python# -*- coding: gb2312 -*-s = '中文's.decode('gb2312').encode('big5')

#! /usr/bin/env python# -*- coding: utf-8 -*-s = '中文'# 即使文件编码为 utf-8,sys 的缺省字符编码仍为 ascii,需要显式设置解码的字符集为 utf-8print s.decode('utf-8')print s.decode('utf-8').encode('gb18030')

是 python 内置函数。将字符串由'charset' 字符集转换为 unicode

unicode (message, charset)

unicode('中文字符串', 'gbk')

unicode('中文字符串', 'gbk').encode('gb18030')

运行命令行 python

用 import 加载程序,模块名为程序名

以 程序名.函数名(参数) 方式调试函数

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