python字元串特點_python 字元串特點

除了數值，Python可以操作字元串，它可以表現在以下幾個方面。包含在單引号或雙引号：

>>> 'spam eggs'

'spam eggs'

>>> 'doesn\'t'

"doesn't"

>>> "doesn't"

"doesn't"

>>> '"Yes," he said.'

'"Yes," he said.'

>>> "\"Yes,\" he said."

'"Yes," he said.'

>>> '"Isn\'t," she said.'

'"Isn\'t," she said.'

字元串可以寫多行。可以用\n表示，下一行是一個合乎邏輯的延續行,最後一個字元用反斜杠：

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

字元串可以被包圍在一對三重引号裡面：

print """

Usage: thingy [OPTIONS]

-h                        Display this usage message

-H hostname               Hostname to connect to

"""

字元串可以被連接配接在一起，用“+”運算符，重複*：

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

>>> word

'HelpA'

>>> ''

''

兩個彼此相鄰的字元串文字自動連接配接：

>>> 'str' 'ing'                   #

'string'

>>> 'str'.strip() + 'ing'   #

'string'

>>> 'str'.strip() 'ing'     #

File "", line 1, in ?

'str'.strip() 'ing'

^

SyntaxError: invalid syntax

注意：word字元串的内容是： “HelpA”  可以是下标(索引)和C一樣，字元串的第一個字元下标(索引)0。可以指定的子串切片标志來表示：兩個指數由冒号分隔。

>>> word[4]

'A'

>>> word[0:2]

'He'

>>> word[2:4]

'lp'

切片索引可以使用預設值;前一個索引預設為零，第二個索引預設被切片的字元串的大小。

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

'He'

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

'lpA'

和C字元串不同，Python字元串不能改變。想修改指定索引位置的字元串會導緻錯誤：

>>> word[0] = 'x'

Traceback (most recent call last):

File "", line 1, in ?

TypeError: object doesn't support item assignment

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

Traceback (most recent call last):

File "", line 1, in ?

TypeError: object doesn't support slice assignment

然而，建立一個新的字元串是簡單而有效的：

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

'xelpA'

>>> 'Splat' + word[4]

'SplatA'

這裡是一個有用的切片操作：[：]+[：]等于。

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

'HelpA'

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

'HelpA'

指數可以是負數，從右邊開始計數。例如：

>>> 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'