Python 2.5 quick reference |  |
Python 2.5 quick reference | |
In addition to the common sequence operations described
in Section 7.1, “Operations common to all the sequence types”, strings support
the format operator
“%”. This extremely
useful operator uses a template
string to specify how to format one or
more values. Here is the general form:
f%v
where fvv
The template string may contain any mixture of ordinary text
and format codes. A format code
always starts with a percent (%) symbol. See
Table 4, “Format codes”.
The result of a format operation consists of the ordinary characters from the template with values substituted within them wherever a format code occurs. A conversational example:
>>> print "We have %d pallets of %s today." % (49, "kiwis") We have 49 pallets of kiwis today.
In the above example, there are two format codes. Code
“%d” means “substitute a
decimal number here,” and code “%s” means “substitute a string value
here”. The number 49 is substituted for the first
format code, and the string "kiwis" replaces
the second format code.
In general, format codes have this form:
%[p][m[.n]]c
Table 3. Parts of the format operator
| An optional prefix; see Table 5, “Format code prefixes”. |
|
Specifies the total desired field width. The
result will never be shorter than this value,
but may be longer if the value doesn't fit;
so, If the value is negative, values are left-aligned in the field whenever they don't fill the entire width. |
|
For float values, this specifies the
number of digits after the decimal point.
|
| Indicates the type of formatting. |
Here are the format type codes, c
Table 4. Format codes
%s |
Format a string. For example, '%-3s' %
'xy' yields 'xy '; the width
(-3) forces left alignment.
|
%d |
Decimal conversion. For example, '%3d' %
-4 yields the string ' -4'.
|
%e |
Exponential format; allow four characters for
the exponent. Examples: '%08.1e' %
1.9783 yields '0002.0e+00'.
|
%E |
Same as %e, but the exponent is shown
as an uppercase E.
|
%f |
For float type. E.g., '%4.1f' %
1.9783 yields ' 2.0'.
|
%g |
General numeric format. Use %f if
it fits, otherwise use %e.
|
%G |
Same as %G, but an uppercase
E is used for the exponent if
there is one.
|
%o |
Octal (base 8). For example, '%o' %
13 yields '15'.
|
%x |
Hexadecimal (base 16). For example, '%x'
% 247 yields 'f7'.
|
%X |
Same as %x, but capital letters
are used for the digits A-F. For example, '%04X'
% 247 yields '00F7'; the
leading zero in the length (04)
requests that Python fill up any empty leading
positions with zeroes.
|
%c |
Convert an integer to the corresponding ASCII code.
For example, '%c' % 0x61 yields the
string 'a'.
|
%% |
Places a percent sign (%) in the
result. Does not require a corresponding
value. Example: "Energy at %d%%." % 88 yields the value 'Energy at 88%.'.
|
Table 5. Format code prefixes
+ | For numeric types, forces the sign to appear even for positive values. |
- | Left-justifies the value in the field. |
0 |
For numeric types, use zero fill. For example,
'%04d' % 2 produces the value
'0002'.
|
# |
With the %o (octal) format, append
a leading "0"; with the
%x (hexadecimal) format, append a
leading "0x"; with the
%g (general numeric) format,
append all trailing zeroes. Examples:
>>> '%4o' % 127 ' 177' >>> '%#4o' % 127 '0177' >>> '%x' % 127 '7f' >>> '%#x' % 127 '0x7f' >>> '%10.5g' % 0.5 ' 0.5' >>> '%#10.5g' % 0.5 ' 0.50000' |