Detailed explanation of str operation in Python

1. str.format(): Use "{}" placeholder to format the string (the index number form and key-value pair form in the placeholder can be mixed).

 1 >>> 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 2 >>> string 3 'python2.7, djangoweb, tornadotornado' 4 >>> string = 'python{}, django{}, tornado{}'.format(2.7, 'web') 5 Traceback (most recent call last): 6   File "<pyshell#6>", line 1, in <module> 7     string = 'python{}, django{}, tornado{}'.format(2.7, 'web') 8 IndexError: tuple index out of range 9 >>> string = 'python{0}, django{2}, tornado{1}'.format(2.7, 'web', 'tornado')  # 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）10 >>> string11 'python2.7, djangotornado, tornadoweb'12 >>> string = 'python{py}, django{dja}, tornado{tor}'.format(tor='tornado', dja='web', py=2.7)  # 可以使用键值对的形式赋值13 >>> string14 'python2.7, djangoweb, tornadotornado'15 >>>

2. Use “%” for string formatting.

# Python automatically determines and converts to %E or %F based on the size of the number##%%

Format symbol table

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

Auxiliary formatting symbol table*-+# before the hexadecimal number. ##0When the size of the number is less than the requirement of m.n, fill it with 0m.nm is displayed The minimum total width of , n is the number of digits after the decimal point (if available)

Define width or decimal point precision
Left-aligned
Output the positive value symbol "+" for positive numbers
The size of the number is insufficient When m.n is required, use spaces to pad
# to display 0 before the octal number and 0x or 0X

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