Python格式化带双引号和dict的字符串

Question

Why formatting with a dict when there is a double quote in the string fails?

'%(x)"%(y)' % {'x': 1, 'y':2}

Traceback (most recent call last):
    File "<stdin>", line 1, in <module>
ValueError: unsupported format character '"' (0x22) at index 4

It works with :

'%s"%s' % (1,2)

Answer 1

You are forgetting the conversion type code:

>>> '%(x)s"%(y)s' % {'x': 1, 'y':2}
'1"2'

Note the s strings. The syntax is %(key)conversiontype . Without a character signalling the conversion type, the parser picks the next character and that's " in your string.

From the string formatting operations documentation :

A conversion specifier contains two or more characters and has the following components, which must occur in this order:

1. The '%' character, which marks the start of the specifier.
2. Mapping key (optional), consisting of a parenthesised sequence of characters (for example, (somename) ).
3. Conversion flags (optional), which affect the result of some conversion types.
4. Minimum field width (optional). If specified as an '*' (asterisk), the actual width is read from the next element of the tuple in values, and the object to convert comes after the minimum field width and optional precision.
5. Precision (optional), given as a '.' (dot) followed by the precision. If specified as '*' (an asterisk), the actual width is read from the next element of the tuple in values, and the value to convert comes after the precision.
6. Length modifier (optional).
7. Conversion type.

You gave items 1 and 2 (which is optional), but omitted item 7.

Answer 2

Just as you use %s , you should use %(x)s . Just as %" is wrong, %(x)" is wrong. You just need to add that little s :

'%(x)s"%(y)s' % {'x': 1, 'y':2}

That letter is required for the same reason it is required in normal formatting. You could, as before, also use d , 03d , f , etc.