python3字符串属性（二）

1、S.isdecimal() -> bool
    Return True if there are only decimal characters in S, False otherwise. 字符串如果是十进制，返回True。

2、S.isdigit() -> bool
     Return True if all characters in S are digits and there is at least one character in S, False otherwise.
3、S.isnumeric() -> bool
    Return True if there are only numeric characters in S,
    False otherwise.

数字

 >>> num=''
 >>> num.isdigit()
 True
 >>> num.isdecimal()
 True
 >>> num.isnumeric()
 True

汉字

 >>> num="二十四"
 >>> num.isdigit()
 False
 >>> num.isdecimal()
 False
 >>> num.isnumeric()
 True

字节（和字符串很像，但在python中不是同一类型）

 >>> num=b''
 >>> num.isdigit()
 True
 >>> num.isdecimal()
 Traceback (most recent call last):
   File "<stdin>", line , in <module>
 AttributeError: 'bytes' object has no attribute 'isdecimal'
 >>> num.isnumeric()
 Traceback (most recent call last):
   File "<stdin>", line , in <module>
 AttributeError: 'bytes' object has no attribute 'isnumeric'

 >>> a=b'abc'
 >>> type(a)
 <class 'bytes'>
 >>> a='abc'
 >>> type(a)
 <class 'str'>

a=b'abc'不是字符串，是字节类型。

"Python的字符串类型是str，在内存中以Unicode表示，一个字符对应若干个字节。如果要在网络上传输，或者保存到磁盘上，就需要把str变为以字节为单位的bytes。"

(http://www.liaoxuefeng.com/wiki/0014316089557264a6b348958f449949df42a6d3a2e542c000/001431664106267f12e9bef7ee14cf6a8776a479bdec9b9000)

4、S.islower() -> bool
    Return True if all cased characters in S are lowercase and there is at least one cased character in S, False otherwise.

字符串里的至少有一个字母且所有的字母为小写

 >>> a='abc'
 >>> a.islower()
 True
 >>> a='abcD'
 >>> a.islower()
 False
 >>> a='abc1'
 >>> a.islower()
 True
 >>> a='abc1-'
 >>> a.islower()
 True
 >>> a='1-'
 >>> a.islower()
 False

5、S.isupper() -> bool
    Return True if all cased characters in S are uppercase and there is
    at least one cased character in S, False otherwise.

用法参见islower()

6、 S.isprintable() -> bool
    Return True if all characters in S are considered printable in repr() or S is empty, False otherwise.

7、S.isspace() -> bool
    
    Return True if all characters in S are whitespace
    and there is at least one character in S, False otherwise.

字符串至少一个字符，且所有字符都是空格。

 >>> a='abc  '
 >>> a.isspace()
 False
 >>> a[:].isspace()
 True

8、  S.istitle() -> bool
    
    Return True if S is a titlecased string and there is at least one
    character in S, i.e. upper- and titlecase characters may only
    follow uncased characters and lowercase characters only cased ones.
    Return False otherwise.

检测字符串中所有的单词拼写首字母是否为大写，且其他字母为小写

 >>> a='Hello World !'
 >>> a.istitle()
 True
 >>> a='Hello World ,huhu!'
 >>> a.istitle()
 False

9、S.join(iterable) -> str
    
    Return a string which is the concatenation of the strings in the
    iterable.  The separator between elements is S.    连接字符.join(可以迭代的字符串)

 >>> a='Hello World ,huhu!'
 >>> '-'.join(a)
 'H-e-l-l-o- -W-o-r-l-d- -,-h-u-h-u-!'

 >>> a=['hello','world','!']
 >>> b='-'
 >>> b.join(a)
 'hello-world-!'

10、S.ljust(width[, fillchar]) -> str            左对齐
    
    Return S left-justified in a Unicode string of length width. Padding is
    done using the specified fill character (default is a space).
方法返回一个原字符串左对齐,并使用空格或其他字符填充至指定长度的新字符串。如果指定的长度小于原字符串的长度则返回原字符串。

 >>> a='abc'
 >>> a.ljust()
 'abc   '
 >>> a.ljust(,'!')
 'abc!!!'
 >>> a.ljust()
 'abc'

11、S.rjust(width[, fillchar]) -> str           右对齐
    
    Return S right-justified in a string of length width. Padding is
    done using the specified fill character (default is a space).

12、S.lower() -> str
    
    Return a copy of the string S converted to lowercase.

13、S.upper() -> str
    
    Return a copy of S converted to uppercase.

 >>> a='Hello World !'
 >>> a.lower()
 'hello world !'
 >>> a.upper()
 'HELLO WORLD !'
 >>> a
 'Hello World !'

14、 S.strip([chars]) -> str    移除头部和尾部字符
    
    Return a copy of the string S with leading and trailing
    whitespace removed.
    If chars is given and not None, remove characters in chars instead.

　　S.lstrip([chars]) -> str    移除头部字符
    
    Return a copy of the string S with leading whitespace removed.
    If chars is given and not None, remove characters in chars instead.

　　S.rstrip([chars]) -> str    移除尾部字符
    
    Return a copy of the string S with trailing whitespace removed.
    If chars is given and not None, remove characters in chars instead.

 >>> a='  hello world !  '
 >>> a.strip()
 'hello world !'
 >>> a.lstrip()
 'hello world !  '
 >>> a.rstrip()
 '  hello world !'
 >>> a
 '  hello world !  '