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1. Python string

String is the most commonly used data type in Python. We can use quotation marks (' or ") to create strings. l

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

>>> var1 = 'hello python' #定義字符串
>>> print(var1[0]) #切片截取，從0開始，不包括截取尾數(shù)
h
>>> print(var1[0:5])
hello
>>> print(var1[-6:])
python
>>> var2 = var1[0:6]+'world' #截取字符并拼接賦值給新變量
>>> print(var2)
hello world

2. Python escape character

\　: At the end of the line, it is the line continuation character

\\　: Backslash escape, output '\'

\'　:Single quote escape

\":Double quote escape

\b　:Backspace

\n　:Line feed

\v　:Vertical tab character

\t　:Horizontal tab character

\r　:Carriage return

\f　:Page change

3. python string operators

(+) splicing, (*) repetition, ( []) index, ([:]) slicing, (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) #重復(fù)輸出字符串
hellohellohello
>>> print(var1[0]) #索引字符串
h
>>> print(var1[3:]) #索引切片
lo
>>> 'e' in var1 #判斷字符串是否在變量中
True
>>> 'p' not in var1 #判斷字符串是否不在變量中
True
>>> print("he\tllo \n") 
he llo 
>>> print(r"he\tllo \n") #原始輸出字符串，也就是原始輸出轉(zhuǎn)義字符
he\tllo \n

4. Formatted strings

Python supports the output of formatted strings. Although this can lead to very complex expressions, the most basic usage is to insert a value into a string with the string formatting character %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 codes
%s	Format string
%d	Format integer
%u	Format unsigned integer
%o	Format unsigned octal number
%x	Format unsigned hexadecimal number
%X	Format unsigned hexadecimal number System number (uppercase)
%f	Format floating point numbers, you can specify the precision after the decimal point
%e	Use scientific notation to format floating point numbers
%E	The function is the same as %e, use scientific notation to format floating point numbers
%g	Abbreviation of %f and %e
%G	Abbreviation of %f and %E
%p	Format the address of a variable as a hexadecimal number

Format operator Auxiliary instructions:

*	Define width or decimal point precision
-	Used for left alignment
+	Display plus sign (+) in front of positive numbers
	Display spaces before positive numbers
	#Display zero ('0') before octal numbers, and before hexadecimal numbers Display '0x' or '0X' (depending on whether 'x' or 'X' is used)
0	The displayed number is filled with '0' in front and Instead of the default space
%	'%%' outputs a single '%'
(var)	Map variable (dictionary parameter)
m.n.	m is the minimum total width of the display, n is the number of digits after the decimal point (if available)

##

>>> print("ascii:%c"%'s') #格式化輸出字符
ascii:s
>>> print("ascii:%c"%'1') #格式化輸出數(shù)字
ascii:1
>>> print("str:%s"%'character string') #格式化字符串
str:character string
>>> print("str:%d"%888) #格式化整數(shù)
str:888
>>> print("str:%f"%888) #格式浮點(diǎn)數(shù)
str:888.000000
>>> print("str:%e"%888) #格式化科學(xué)計(jì)數(shù)浮點(diǎn)數(shù)
str:8.880000e+02
>>> print("str:%E"%888) #同上
str:8.880000E+02
>>> print("str:%G"%888) #%f和%E的簡(jiǎn)寫
str:888

>>> print("str:%20f"%888.089) #定義20寬度輸出
str:  888.089000
>>> print("str:%-20f"%888.089) #用左對(duì)齊
str:888.089000  
>>> print("str:%+20f"%888.089) #在正數(shù)前顯示加號(hào)
str:  +888.089000
>>> print("str:%+-20f"%888.089) #左對(duì)齊顯示加號(hào)
str:+888.089000  
>>> print("str:%020f"%888.089) #以0填充默認(rèn)的空格
str:0000000000888.089000
>>> print("str:%%%20f"%888.089) #在數(shù)字前輸入%號(hào)
str:%  888.089000
>>> print("str:%%%-20f"%888.089) #左對(duì)齊輸出%號(hào)
str:%888.089000  
>>> print("str:%20.3f"%888.089) #顯示最小總寬度20，小數(shù)點(diǎn)后位數(shù)為3位
str:  888.089

Since python2.6, the format string function str.format():

usage has been added : It uses {} and : to replace %

Positional parameters are not subject to order constraints, and can be {} empty, as long as there is a corresponding parameter value in the format. If the parameter value is not enough, an error will be reported. The parameter index starts from 0, and the incoming positional parameter list can be *list

In [27]: '{}+{}={}'.format(1,2,3) #格式化按順序應(yīng)用參數(shù)值
Out[27]: '1+2=3'
In [28]: '{2}-{1}={0}'.format(1,2,3) #指定順序應(yīng)用參數(shù)值
Out[28]: '3-2=1'
In [29]: '{0}+{0}={1}'.format(2,3) #指定參數(shù)可以重復(fù)使用
Out[29]: '2+2=3'
In [30]: '{}+{}={}'.format(2,3) #如不指定順序，format參數(shù)不夠就會(huì)報(bào)錯(cuò)
---------------------------------------------------------------------------
IndexError    Traceback (most recent call last)
<ipython-input-30-29f40e412920> in <module>()
----> 1 &#39;{}+{}={}&#39;.format(2,3)
IndexError: tuple index out of range

In [31]: l1 = [2,4,8] 
In [32]: &#39;{}*{}={}&#39;.format(*l1) #使用列表引用參數(shù)值
Out[32]: &#39;2*4=8&#39;

In [33]: dct = {&#39;name&#39;:&#39;python&#39;,&#39;age&#39;:20} #定義字典
In [35]: &#39;welcom to {name},age is {age}&#39;.format(name=&#39;qi&#39;,age=28) #變量引用
Out[35]: &#39;welcom to qi,age is 28&#39;

In [36]: &#39;welcom to {name},age is {age}&#39;.format(**dct) #使用**引用字典參數(shù)必須填寫key值
Out[36]: &#39;welcom to python,age is 20&#39;

填充與格式化：
In [53]: "{0: >20}".format("string") #從0位開始已空格填充20寬度左對(duì)齊
Out[53]: &#39;  string&#39;

In [54]: "{0:&>20}".format("string")
Out[54]: &#39;&&&&&&&&&&&&&&string&#39;

In [55]: "{0:#>20}".format("string") #使用#號(hào)會(huì)有個(gè)小bug
 ....: 
Out[55]: &#39;##############string&#39;

In [60]: &#39;{0:+<20}&#39;.format("string") #向右對(duì)齊填充+
Out[60]: &#39;string++++++++++++++&#39;

In [61]: &#39;{0:+^20}&#39;.format("string") #劇中對(duì)齊填充+
Out[61]: &#39;+++++++string+++++++&#39;

精度與進(jìn)制：
>>> &#39;{0:.3f}&#39;.format(10/3) #小數(shù)位進(jìn)度格式化
&#39;3.333&#39;
>>> &#39;{0:b}&#39;.format(8) #格式化二進(jìn)制
&#39;1000&#39;
>>> &#39;{0:o}&#39;.format(9) #格式化八進(jìn)制
&#39;11&#39;
>>> &#39;{0:x}&#39;.format(26) #格式化十六進(jìn)制
&#39;1a&#39;
>>> &#39;{0:,}&#39;.format(123456789) #千分位格式化
&#39;123,456,789&#39;

使用索引：
>>> l2 = [&#39;AA&#39;,{&#39;bb&#39;:&#39;cc&#39;},(&#39;d&#39;,&#39;e&#39;)] #列表索引引用
>>> &#39;outing:{0[0]}&#39;.format(l2) 
&#39;outing:AA&#39;
>>> &#39;outing:{0[0]},{0[1]}&#39;.format(l2) #將列表當(dāng)成一個(gè)元素，在其中索引值
"outing:AA,{&#39;bb&#39;: &#39;cc&#39;}"

5. Python's string method

>>> s = 'i mi to' #將字符串的第一個(gè)字符改為大寫
>>> s.capitalize()
'I mi to'

>>> s = 'I MI TO' #將字符串所有字符改為小寫
>>> s.casefold()
'i mi to'

>>> s.center(15) #將字符串劇中，并用空格將字符串填充長(zhǎng)度，如指定長(zhǎng)度小于實(shí)際長(zhǎng)度則沒有效果
' I MI TO '

>>> s = 'abcabcabcabc' #返回sub在字符串里出現(xiàn)的次數(shù)，start，end為可選參數(shù)，決定范圍
>>> s.count('a',0,12)
4
>>> s.encode(encoding='utf-8',errors='strict') #以encoding指定的編碼格式對(duì)字符串進(jìn)行編碼
b'abcabcabcabc'
>>> s.endswith('abc',1,12) #檢查字符串是否以sub結(jié)尾，是返回True,否返回False，start，end為可選參數(shù)，決定范圍
True

>>> s = 'a\tb\tc'
>>> s.expandtabs(4) #把字符串的tab字符（\t）轉(zhuǎn)化為空格，如不指定tabsize,默認(rèn)為8個(gè)空格
'a b c'

>>> s.find('b') #檢測(cè)字符串是否在字符串中，如在則返回索引，否則返回-1，可指定起始值。
2

>>> s='hello python'
>>> s.index('hello') # 類似find()，不同在于如果sub不在字符串中，返回異常
0 

>>> s.isalnum() #有空格返回false
False
>>> s='hellopython'
>>> s.isalnum() #如果字符串至少有一個(gè)字符，并且所有字符都是字母或數(shù)字則返回True,否則False
True
>>> s.isalpha() #如果字符串至少有一個(gè)字符，并且所有字符都是字母則返回True,否則False
True

>>> s = '123'
>>> s.isdigit() #如果字符串只包含數(shù)字則返回True,否則返回False
True

>>> s = '123'
>>> s.isdecimal() #如果字符串只包含十進(jìn)制數(shù)字則返回True，否則返回False
True
>>> 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個(gè)能區(qū)分大小寫的字符，并且這些字符都是小寫則返回True,否則返回Flase
True
>>> s = 'Abc'
>>> s.islower()
False

>>> s = 'ABC'
>>> s.isupper() #果字符中至少包含一個(gè)能區(qū)分大小寫的字符，并且這些字符都是大寫則返回True,否則返回Flase
True
>>> s = 'ABc'
>>> s.isupper()
False
>>> 

>>> s = '123'
>>> s.isnumeric() #如果字符串只包含數(shù)字字符，則返回True,否則返回False
True
>>> s = '123a'
>>> s.isnumeric()
False

>>> 'def'.isidentifier() #判斷字符串是否包含該語言的保留字
True

>>> 'aaa'.isprintable() #判斷是否可以打印
True

>>> ''.isspace()
False
>>> ' '.isspace() #判斷字符串中至少有一個(gè)字符且所有都是空格，否則返回false
True
>>> ' a'.isspace()
False

>>> 'Abc'.istitle() #判斷是否是標(biāo)題 格式，可以理解為首字母大寫。
True
>>> 'aBC'.istitle()
False

>>> s = '123'
>>> '_'.join(s) #返回一個(gè)用指定字符串分隔的字，或者是將指定字符加入到另一個(gè)字符中。
'1_2_3'
>>> s.join('abc')
'a123b123c'

>>> s = 'ABC'
>>> s.lower() #返回的是指定字符串的拷貝，并轉(zhuǎn)化成小寫
'abc'

>>> s.ljust(10,'+') #可以指定寬度，以及填充字符串，返回的是按寬度，填充字符串格式化后的左對(duì)齊的字符串。
'ABC+++++++'

>>> 'aaabccc'.partition('b') #在字符串中查找指定的字符，如找到則返回字符前部分，字符本身和后部分，如沒找到則返回字符串和兩個(gè)空字符串。
('aaa', 'b', 'ccc')
>>> 'aaabccc'.partition('e')
('aaabccc', '', '')

>>> 'aaabccc'.rpartition('b') #與partition一樣，但是是從右邊開始
('aaa', 'b', 'ccc')
>>> 'aaabccc'.rpartition('c')
('aaabcc', 'c', '')


>>> 'aaaaabbcc'.replace('a','A') #用指定字符串替換指定字符串，如果不指定替換次數(shù)，則替換所有
'AAAAAbbcc'
>>> 'aaaaabbcc'.replace('a','A',2)
'AAaaabbcc'

>>> 'aabbcc'.rfind('a') #返回指定子串的最高索引，如果沒找到則返回-1，可以指定要開始替換的起始，結(jié)束位置。
1
>>> 'aabbcc'.rfind('e')
-1
>>> 'aabbcc'.rindex('a') #與上面的rfind一樣，只是如果沒找到不是返回-1，而是觸發(fā)錯(cuò)誤
1
>>> 'aabbcc'.rindex('e')
Traceback (most recent call last):
 File "<stdin>", line 1, in <module>
ValueError: substring not found

>>> &#39;aa&#39;.rjust(10,&#39;+&#39;) #與ljust()相對(duì)應(yīng)，右對(duì)齊
&#39;++++++++aa&#39;
>>> &#39;aa&#39;.ljust(10,&#39;+&#39;)
&#39;aa++++++++&#39;

>>> &#39;aabccbddbee&#39;.split(&#39;b&#39;) ##按指定字符串對(duì)目標(biāo)字符串進(jìn)行切割，可以指定切割次數(shù)
[&#39;aa&#39;, &#39;cc&#39;, &#39;dd&#39;, &#39;ee&#39;]
>>> &#39;aabccbddbee&#39;.split(&#39;b&#39;,2)
[&#39;aa&#39;, &#39;cc&#39;, &#39;ddbee&#39;]

>>> &#39;aabccbddbee&#39;.rsplit(&#39;b&#39;,2) #與split作用相同，但是從右側(cè)開始
[&#39;aabcc&#39;, &#39;dd&#39;, &#39;ee&#39;]

>>> &#39; aabb &#39;.strip() #移除字符串兩側(cè)的指定字符串，默認(rèn)移除空格，需要注意的是可以指定多個(gè)字符
&#39;aabb&#39;
>>> &#39; aabb&#39;.strip(&#39;b&#39;)
&#39; aa&#39;
>>> &#39; aabb&#39;.strip(&#39;ab&#39;)
&#39; &#39;
>>> &#39;beaacebb&#39;.rstrip(&#39;eb&#39;) #與strip一樣，從右側(cè)刪除指定字符，可以為多個(gè)
&#39;beaac&#39;

>>> &#39;aa\nbb\ncc\ndd&#39;.splitlines() #按換行符切割顯示，如沒指定keepends=True則將換行符移除。
[&#39;aa&#39;, &#39;bb&#39;, &#39;cc&#39;, &#39;dd&#39;]
>>> &#39;aa\nbb\ncc\ndd&#39;.splitlines(keepends=True)
[&#39;aa\n&#39;, &#39;bb\n&#39;, &#39;cc\n&#39;, &#39;dd&#39;]

>>> &#39;aabbc&#39;.startswith(&#39;a&#39;) #判斷字符串是否以某個(gè)字符開頭，可以是多字符
True
>>> &#39;aabbc&#39;.startswith(&#39;b&#39;)
False
>>> &#39;aabbc&#39;.startswith(&#39;aab&#39;)
True

>>> &#39;aaBBcc&#39;.swapcase() #轉(zhuǎn)換大小寫
&#39;AAbbCC&#39;

>>> &#39;wend is ok&#39;.title() #標(biāo)題格式，首字母大寫，其它字符小寫
&#39;Wend Is Ok&#39;

>>> &#39;wend is ok&#39;.upper() #將字符全部轉(zhuǎn)換成大寫
&#39;WEND IS OK&#39;

>>> &#39;wend is ok&#39;.zfill(20) #這里的z指zero，用0將字符填充到指定長(zhǎng)度
&#39;0000000000wend is ok&#39;

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