Explanation of str related operations in Python

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1. str.format(): Use “{}” placeholder to format the string (the index number form in the placeholder and Key-value pairs can be mixed).

>>> string = 'python{}, django{}, tornado{}'.format(2.7, 'web', 'tornado') # 有多少个{}占位符就有多少个值与其对应，按照顺序“填”进字符串中
>>> string
'python2.7, djangoweb, tornadotornado'
>>> string = 'python{}, django{}, tornado{}'.format(2.7, 'web')
Traceback (most recent call last):
 File "<pyshell#6>", line 1, in <module>
  string = &#39;python{}, django{}, tornado{}&#39;.format(2.7, &#39;web&#39;)
IndexError: tuple index out of range
>>> string = &#39;python{0}, django{2}, tornado{1}&#39;.format(2.7, &#39;web&#39;, &#39;tornado&#39;) # 也可以指定“填”进去的值（从0开始，后面的值不一定都要用上，但是要保证指定的位置是有值的）
>>> string
&#39;python2.7, djangotornado, tornadoweb&#39;
>>> string = &#39;python{py}, django{dja}, tornado{tor}&#39;.format(tor=&#39;tornado&#39;, dja=&#39;web&#39;, py=2.7) # 可以使用键值对的形式赋值
>>> string
&#39;python2.7, djangoweb, tornadotornado&#39;
>>>

2. Use "%" for string formatting.

Format symbol table

##%G is automatically judged and converted to %E or %F% by Python based on the size of the number. Output "%"

%c	Convert to a single character
#%r	Convert to a string expressed using repr()
%s	Convert to a string expressed using str()
%d or %i	Convert to a signed decimal integer
%u	Convert to unsigned decimal integer
%o	Convert to unsigned octal integer
%x	Convert to unsigned hexadecimal integer, hexadecimal letters are represented in lowercase
%X	is converted to an unsigned hexadecimal integer, hexadecimal letters are expressed in uppercase letters
%e	is converted to scientific notation Floating point number, the e in which is represented by lowercase
%E	is converted into a floating point number expressed in scientific notation, where the E is represented by uppercase
%f or #F	is converted to a floating point number
%g	is automatically determined by Python and converted to % based on the size of the number e or %f

##Auxiliary formatting symbol table

*-+0m.n

Define width or decimal point precision
Left-aligned
Output the positive value symbol "+" for positive numbers
When the size of the number is less than the requirement of m.n , use spaces to pad
# to display 0 before the octal number, and to display 0x or 0X before the hexadecimal number
When the size of the number is less than the requirement of m.n, fill it with 0
m is the minimum total width displayed , n is the number of digits after the decimal point (if available)

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