string

多行文本以\结尾，换行还是要用\n

hello = "This is a rather long string containing\n\

several lines of text just as you would do in C.\n\

    Note that whitespace at the beginning of the line is\

 significant."



print(hello)

多行原格式文本用"""或者'''围绕。里面的换行就是换行

print("""\

Usage: thingy [OPTIONS]

     -h                        Display this usage message

     -H hostname               Hostname to connect to

""")

string可以用+号和*号

>>> word = 'Help' + 'A'

>>> word

'HelpA'

>>> '<' + word*5 + '>'

'<HelpAHelpAHelpAHelpAHelpA>'

string可以被索引[]

>>> word[4]

'A'

>>> word[0:2]

'He'

>>> word[2:4]

'lp'

>>> word[:2]    # The first two characters

'He'

>>> word[2:]    # Everything except the first two characters

'lpA'

python中的string是不可改变的，只能从新创建字符串，和c不同

>>> word[0] = 'x'

Traceback (most recent call last):

  File "<stdin>", line 1, in ?

TypeError: 'str' object does not support item assignment

>>> word[:1] = 'Splat'

Traceback (most recent call last):

  File "<stdin>", line 1, in ?

TypeError: 'str' object does not support slice assignment



#只能从新创建字符串

>>> 'x' + word[1:]

'xelpA'

>>> 'Splat' + word[4]

'SplatA'



>>> word[:2] + word[2:]

'HelpA'

>>> word[:3] + word[3:]

'HelpA'

索引没有越界问题

>>> word[1:100]

'elpA'

>>> word[10:]

''

>>> word[2:1]

''

索引可以是负值，从右往左数字符

>>> word[-1]     # The last character

'A'

>>> word[-2]     # The last-but-one character

'p'

>>> word[-2:]    # The last two characters

'pA'

>>> word[:-2]    # Everything except the last two characters

'Hel'

 +---+---+---+---+---+

 | H | e | l | p | A |

 +---+---+---+---+---+

 0   1   2   3   4   5

-5  -4  -3  -2  -1

len()内置函数用来得到字符长度

>>> s = 'supercalifragilisticexpialidocious'

>>> len(s)

34

 合并迭代子

>>> def concat(*args, sep="/"):

...    return sep.join(args)

...

>>> concat("earth", "mars", "venus")

'earth/mars/venus'

>>> concat("earth", "mars", "venus", sep=".")

'earth.mars.venus'

 赋值技巧

>>> string1, string2, string3 = '', 'Trondheim', 'Hammer Dance'

>>> non_null = string1 or string2 or string3

>>> non_null

'Trondheim'