Example of Python character string

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1. Python string

The string is the most commonly used data type in Python. We can use quotation marks (' or ') to create a string, L

Python does not support single character types, and one character is also used as a string in Python.

>>> var1 = ' Hello python ' #定义字符串 >>> print (var1[0]) #切片截取, starting from 0, excluding truncated mantissa h>>> print (Var1[0:5]) hello>>> print (var1[-6:]) python>>> var2 = var1[0:6]+ ' world ' #截取字符并拼接赋值给新变量 >>> print (VAR2) Hello World

2. Python escape character

\: line-continuation character at end of row

\ \: Anti-slash escape, output ' \ '

\ ': Single quote escaping

\ ": Double quote Escape

\b: Backspace (BACKSPACE)

\ n: Line break

\v: Portrait tab

\ t: Horizontal tab

\ r: Enter

\f: Page Change

3. Python string operator

(+) splicing, (*) repetition, ([]) index, ([:]) slice, (in) member judgment, (not in) non-member judgment, (R/R) element output string

>>> var1 = ' Hello ' >>> var2 = ' python ' >>> print (var1+var2) #拼接字符串hellopython >>> Print (var1*3) #重复输出字符串hellohellohello >>> print (var1[0]) #索引字符串h >>> print (var1[3:]) #索引切片lo >  >> ' e ' in var1 #判断字符串是否在变量中True >>> ' P ' var1 #判断字符串是否不在变量中True >>> print ("He\tllo \ n") he Llo >>> print (r "He\tllo \ n") #原始输出字符串, which is the original output escape character He\tllo \ n

4. Formatting strings

Python supports the output of formatted strings. Although this may use a very complex expression, the most basic usage is to insert a value into a string that has the string format of%s.

In Python, string formatting uses the same syntax as the sprintf function in C.

Python string formatting symbols:

%c	Formatting characters and their ASCII code
%s	formatting strings
%d	formatting integers
%u	Formatting an unsigned integer
%o	Formatting an unsigned octal number
%x	formatting unsigned hexadecimal numbers
%x	Format unsigned hexadecimal number (uppercase)
%f	Format floating-point numbers to specify the precision after a decimal point
%e	Format floating-point numbers with scientific notation
%E	function with%e, format floating-point numbers with scientific notation
%g	Shorthand for%f and%e
%G	Shorthand for%f and%E
%p	Format the address of a variable with hexadecimal number

Formatting operator Auxiliary directives:

*	Define width or decimal precision
-	Used for left justification
+	Show plus sign (+) in front of positive number
<sp>	Show spaces in front of positive numbers
#	Displays 0 (' 0 ') before the octal number, preceded by ' 0x ' or ' 0X ' in hexadecimal (depending on ' x ' or ' x ')
0	The displayed number is preceded by ' 0 ' instead of the default space
%	' percent ' output a single '% '
(VAR)	mapping variables (dictionary parameters)
M.N.	M is the minimum total width displayed, and n is the number of digits after the decimal point (if available)

>>> print ("ascii:%c"% ' s ') #格式化输出字符ascii:s>>> print ("ascii:%c"% ' 1 ') #格式化输出数字ascii:1>>> Print ("str:%s"% ' character string ') #格式化字符串str: Character string>>> print ("str:%d"%888) #格式化整数str:888> >> print ("str:%f"%888) #格式浮点数str:888.000000>>> print ("str:%e"%888) #格式化科学计数浮点数str:8.880000e+02> >> print ("str:%e"%888) #同上str:8.880000e+02>>> print ("str:%g"%888) #%f and%E abbreviated str:888>>> print ("str:%20f"%888.089) #定义20宽度输出str:888.089000>>> print ("str:%-20f"%888.089) #用左对齐str: 888.089000 >> > Print ("str:%+20f"%888.089) #在正数前显示加号str: +888.089000>>> print ("str:%+-20f"%888.089) #左对齐显示加号str: + 888.089000 >>> Print ("str:%020f"%888.089) #以0填充默认的空格str:0000000000888.089000>>> print ("str:%%% 20f "%888.089) #在数字前输入% str:% 888.089000>>> print (" str:%%%-20f "%888.089) #左对齐输出% str:%888.089000 >> > Print ("str:%20.3f"%888.089) #显示最小总宽度20, 3 digits after the decimal point str:888.089

Starting from python2.6, add the formatted string function Str.format ():

To use: It replaces% with {} and:

Positional parameters are not constrained by order, and can be {} null, as long as there is a corresponding parameter value in format, such as the parameter value is not enough error, parameter index from 0, passed in the location parameter list available * list

in [+]: ' {}+{}={} '. Format (No. 28): ' 1+2=3 ' in []: ' {2}-{1}={0} '. Format () ' 3-2=1 ' in []: ' {0}+{0}={1} '. Format (2,3) #指定参数可以重复使用Out [+]: ' 2+2=3 ' in []: ' {}+{}={} '. Format (2,3) #如不指定顺序, If the format parameter is insufficient, the error will be---------------------------------------------------------------------------Indexerror Traceback ( Most recent call last) <ipython-input-30-29f40e412920> in <module> ()----> 1 ' {}+{}={} '. Format (2,3) Indexerror:tuple index out of Rangein [+]: L1 = [2,4,8] in [+]: ' {}*{}={} '. Format (*L1) #使用列表引用参数值Out [+]: ' 2*4=8 ' in [33 ]: DCT = {' name ': ' Python ', ' age ': ' 35} #定义字典In [+]: ' welcom to {name},age are {age} '. Format (name= ' qi ', age=28) #变量引用Out []: ' Welcom to Qi,age is "in [+]: ' welcom to {name},age are {age} '. Format (**DCT) #使用 * * Reference dictionary parameter must be filled with key value out[36]: ' Welcom to Pytho N,age is 20 ' Fill and format: in [+]: ' {0: >20} '. Format ("string") #从0位开始已空格填充20宽度左对齐Out [+]: ' String ' in [si]: ' {0:&>20} ". Format (" string ") out[54]: ' &AMP;&AMP;&AMP;&AMP;&AMP;&AMP;&AMp;&&&&&&&string ' in []: ' {0:#>20} '. Format ("string") #使用 # number will have a small bug ....: out[55]: ' # # ########### #string ' in [+]: ' {0:+<20} '. Format ("string") #向右对齐填充 +out[60]: ' string++++++++++++++ ' in [61]: ' {0:+^20} '. Format ("string") #剧中对齐填充 +out[61]: ' +++++++string+++++++ ' precision with:>>> ' {0:.3f} '. Format (10/3) #小数位进度格式化 ' 3. 333 ' >>> ' {0:b} '. Format (8) #格式化二进制 ' + ' >>> ' {0:o} '. Format (9) #格式化八进制 ' one ' >>> ' {0:x} '. Format (+) #格式化十六进制 ' 1a ' >>> ' {0:,} '. Format (123456789) #千分位格式化 ' 123,456,789 ' using index:>>> l2 = [' AA ', {' BB ' : ' CC '}, (' d ', ' e ')] #列表索引引用 >>> ' outing:{0[0]} '. Format (L2) ' Outing:aa ' >>> ' outing:{0[0]},{0[1]} '. Format (L2) #将列表当成一个元素 in which the index value "outing:aa,{' BB ': ' CC '}"

5. Python string method

>>> s = ' i mi to ' #将字符串的第一个字符改为大写 >>> s.capitalize () ' I mi to ' >>> s = ' i mi to ' #将字符串所有字符改为小写 > >> s.casefold () ' I mi to ' >>> s.center (#将字符串剧中), with a space to fill the string with length, if the specified length is less than the actual length then no effect ' I mi to ' >>> s = ' Abcabcabcabc ' #返回sub在字符串里出现的次数, start,end for optional parameters, decision range >>> S.count (' A ', 0,12) 4>>> S.encode (encoding= ' Utf-8 ', errors= ' strict ') #以encoding指定的编码格式对字符串进行编码b ' abcabcabcabc ' >>> s.endswith (' abc ', 1,12) # Checks whether the string ends with a sub, returns True, no returns false,start,end as an optional parameter, determines the range true>>> s = ' A\TB\TC ' >>> s.expandtabs (4) # Converts the tab character of a string (\ t) to a space, such as not specifying Tabsize, the default is 8 spaces ' a b C ' >>> s.find (' B ') #检测字符串是否在字符串中, if the index is returned, otherwise returns-1, you can specify the starting value. 2>>> s= ' Hello python ' >>> s.index (' Hello ') # similar to find (), except that if the sub is not in the string, return exception 0 >>> s.isalnum () #有空格返回falseFalse >>> s= ' Hellopython ' >>> s.isalnum () #如果字符串至少有一个字符, and all characters are letters or numbers return true, otherwise falsetrue>>> S.isalpha () #如果字符串至少有一个字符, and all characters are alphabetic returns true, otherwise falsetrue>>> s = ' 123 ' &GT;>> s.isdigit () #如果字符串只包含数字则返回True, otherwise return falsetrue>>> s = ' 123 ' >>> s.isdecimal () # Returns True if the string contains only decimal digits, otherwise returns falsetrue>>> s= ' ox123 ' >>> s.isdecimal () false>>> s = ' 0.33 ' > >> S.isdecimal () false>>> s = ' abc ' >>> S.islower () #如果字符中至少包含一个能区分大小写的字符, and these characters are lowercase to return true, Otherwise return flasetrue>>> s = ' abc ' >>> S.islower () false>>> s = ' abc ' >>> S.isupper () # The fruit character contains at least one case-sensitive character, and the characters are uppercase to return true, otherwise return flasetrue>>> s = ' ABc ' >>> s.isupper () false>>> >>> s = ' 123 ' >>> s.isnumeric () #如果字符串只包含数字字符, returns true otherwise falsetrue>>> s = ' 123a ' >> > s.isnumeric () false>>> ' Def '. Isidentifier () #判断字符串是否包含该语言的保留字True >>> ' aaa '. isprintable () # Determine if you can print true>>> '. Isspace () false>>> ". Isspace () #判断字符串中至少有一个字符且所有都是空格, otherwise return falsetrue>> > ' a '. isspace () false>>> ' ABC '. Istitle () #判断是否是标题 format, which can be understood as the first letter capitalized. True>>> ' ABC '. IStitle () false>>> s = ' 123 ' >>> ' _ '. Join (s) #返回一个用指定字符串分隔的字, or add the specified character to another character. ' 1_2_3 ' >>> s.join (' abc ') ' a123b123c ' >>> s = ' abc ' >>> S.lower () #返回的是指定字符串的拷贝 and converted to lowercase ' abc ' >>> s.ljust (' + ') #可以指定宽度, as well as padding strings, returns a string that is left-aligned after the string is formatted by the width of the fill. ' abc+++++++ ' >>> ' AAABCCC '. partition (' B ') #在字符串中查找指定的字符, if found, returns the first part of the character, the character itself and the back part, and returns a string and two empty strings, if not found. (' AAA ', ' B ', ' CCC ') >>> ' AAABCCC '. partition (' E ') (' AAABCCC ', ' ', ') >>> ' AAABCCC '. Rpartition (' B ') # Same as partition, but starting from the right (' AAA ', ' B ', ' CCC ') >>> ' AAABCCC '. rpartition (' C ') (' aaabcc ', ' C ', ') >>> ' AAAAABBCC '. Replace (' A ', ' a ') #用指定字符串替换指定字符串, replace all ' aaaaabbcc ' >>> ' aaaaabbcc ' If you do not specify a replacement number. Replace (' A ', ' a ', 2) ' AAAAABBCC ' >>> ' aabbcc '. RFind (' a ') #返回指定子串的最高索引, if not found, returns-1, which specifies the starting and ending position to start the substitution. 1>>> ' AABBCC '. RFind (' e ') -1>>> ' aabbcc '. Rindex (' a ') #与上面的rfind一样, just if not found not return-1, but trigger error 1>> > ' AABBCC ' rindex (' e ') Traceback (most recent call last): File "<stdin>", LIne 1, in <module>valueerror:substring not found>>> ' AA '. Rjust (, ' + ') corresponds to #与ljust (), right-aligned ' ++++++++AA ' >>> ' AA '. Ljust (' + ') ' aa++++++++ ' >>> ' Aabccbddbee '. Split (' B ') # #按指定字符串对目标字符串进行切割, you can specify the number of cuts [' AA ' , ' CC ', ' dd ', ' ee ']>>> ' Aabccbddbee '. Split (' B ', 2) [' AA ', ' cc ', ' Ddbee ']>>> ' Aabccbddbee '. Rsplit (' B ', 2) #与split作用相同, but start from the right [' aabcc ', ' dd ', ' ee ']>>> ' aabb '. Strip () #移除字符串两侧的指定字符串, by default remove spaces, note that you can specify more than one character ' Aabb ' >>> ' Aabb ' strip (' B ') ' AA ' >>> ' Aabb '. Strip (' ab ') ' >>> ' Beaacebb '. Rstrip (' EB ') #与strip一样, Removes the specified character from the right, and can be used for multiple ' beaac ' >>> ' aa\nbb\ncc\ndd '. Splitlines () #按换行符切割显示 and remove newline characters if no keepends=true is specified. [' AA ', ' BB ', ' cc ', ' dd ']>>> ' aa\nbb\ncc\ndd '. Splitlines (keepends=true) [' aa\n ', ' bb\n ', ' cc\n ', ' DD ']>> > ' AABBC '. StartsWith (' a ') #判断字符串是否以某个字符开头, can be multi-character true>>> ' AABBC '. StartsWith (' B ') false>>> ' Aabbc '. StartsWith (' AaB ') true>>> ' aabbcc '. Swapcase () #转换大小写 ' aabbcc ' >>> ' Wend IS OK '. Title () #标题格式, first letter uppercase, other characters lowercase ' wend is ok ' >>> ' wend are OK '. Upper () #将字符全部转换成大写 ' wend is ok ' >>> ' wend ' Ok '. Zfill #这里的z指zero, fill the character with 0 to the specified length ' 0000000000wend is ok '