Details of Python str operation method of

str. format() : Format the string with "{}" placeholders (the index-number form and key-value pair form in placeholders can be mixed).

>>> string = 'python{}, django{}, tornado{}'.format(2.7, 'web', 'tornado') #  How many {} A placeholder is a number of values that are "filled" into the string in order 
>>> 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 = 'python{}, django{}, tornado{}'.format(2.7, 'web')
IndexError: tuple index out of range
>>> string = 'python{0}, django{2}, tornado{1}'.format(2.7, 'web', 'tornado') #  You can also specify values to "fill in" (from 0 I'm going to start off with no 1 Use all, but make sure that the specified location has a value) 
>>> string
'python2.7, djangotornado, tornadoweb'
>>> string = 'python{py}, django{dja}, tornado{tor}'.format(tor='tornado', dja='web', py=2.7) #  Assignments can be made in the form of key-value pairs 
>>> string
'python2.7, djangoweb, tornadotornado'
>>>

2. Use "%" for string formatting.

Format symbol table

Auxiliary formatting symbol table