On Fri, Feb 13, 2009 at 6:19 AM, Antoine Pitrou <solipsis@pitrou.net> wrote:
Guido van Rossum <guido@...> writes:
I don't intend to force the issue. I'm disappointed though -- .format() fixes several common stumbling blocks with %(name)s and at least one with %s.
Everytime I try to experiment a bit with format codes, I find them unintuitively complex:
"{0!r}".format(2.5) '2.5' "{0:r}".format(2.5) Traceback (most recent call last): File "<stdin>", line 1, in <module> ValueError: Unknown conversion type r "{0!f}".format(2.5) Traceback (most recent call last): File "<stdin>", line 1, in <module> ValueError: Unknown conversion specifier f "{0:f}".format(2.5) '2.500000'
Why must the 'f' code be preceded by a colon rather than by an exclamation mark?
Actually, !r is the exception. The rule is that a colon is followed by a formatting language specific to type type, e.g. {:f} (which is only supported by floating point numbers and means fixed-point), whereas an exclamation point is followed by a single letter that bypasses the type-specific formatting -- {!r} is really the only one you need to learn.
There is surely a rational explanation, but in day-to-day use it is really confusing. Add to this the annoyance of typing ".format" and of adding curly braces everywhere, and "%" is clearly handier despite the lonely tuple problem.
It is true that the advantages of .format() are probably more appreciated when you are writing a larger program. -- --Guido van Rossum (home page: http://www.python.org/~guido/)