String and Unicode objects have one unique built-in operation: the
% operator (modulo). This is also known as the string
formatting or interpolation operator. Given
format % values (where format is a string or
% conversion specifications in format
are replaced with zero or more elements of values. The effect
is similar to the using sprintf() in the C language. If
format is a Unicode object, or if any of the objects being
converted using the
%s conversion are Unicode objects, the
result will be a Unicode object as well.
If format requires a single argument, values may be a single non-tuple object. 2.8 Otherwise, values must be a tuple with exactly the number of items specified by the format string, or a single mapping object (for example, a dictionary).
A conversion specifier contains two or more characters and has the following components, which must occur in this order:
If the right argument is a dictionary (or any kind of mapping), then the formats in the string must have a parenthesized key into that dictionary inserted immediately after the "%" character, and each format formats the corresponding entry from the mapping. For example:
>>> count = 2 >>> language = 'Python' >>> print '%(language)s has %(count)03d quote types.' % vars() Python has 002 quote types.
In this case no
* specifiers may occur in a format (since they
require a sequential parameter list).
The conversion flag characters are:
|#||The value conversion will use the ``alternate form'' (where defined below).|
|0||The conversion will be zero padded for numeric values.|
|-||The converted value is left adjusted (overrides the "0" conversion if both are given).|
|(a space) A blank should be left before a positive number (or empty string) produced by a signed conversion.|
|+||A sign character ("+" or "-") will precede the conversion (overrides a "space" flag).|
The length modifier may be
L may be
present, but are ignored as they are not necessary for Python.
The conversion types are:
|d||Signed integer decimal.|
|i||Signed integer decimal.|
|x||Unsigned hexidecimal (lowercase).||(2)|
|X||Unsigned hexidecimal (uppercase).||(2)|
|e||Floating point exponential format (lowercase).|
|E||Floating point exponential format (uppercase).|
|f||Floating point decimal format.|
|F||Floating point decimal format.|
|g||Same as "e" if exponent is greater than -4 or less than precision, "f" otherwise.|
|G||Same as "E" if exponent is greater than -4 or less than precision, "F" otherwise.|
|c||Single character (accepts integer or single character string).|
|r||String (converts any python object using repr()).||(3)|
|s||String (converts any python object using str()).||(4)|
|%||No argument is converted, results in a "%" character in the result.|
'0X'(depending on whether the "x" or "X" format was used) to be inserted between left-hand padding and the formatting of the number if the leading character of the result is not already a zero.
%rconversion was added in Python 2.0.
Since Python strings have an explicit length,
do not assume that
'\0' is the end of the string.
For safety reasons, floating point precisions are clipped to 50;
%f conversions for numbers whose absolute value is over 1e25
are replaced by
%g conversions.2.9 All other errors raise exceptions.
Additional string operations are defined in standard modules string and re.