On Fri, 29 Jun 2012 09:31:53 -0700, Josh English wrote:
> I have a list of tuples, and usually print them using:
>
> print c, " ".join(map(str, list_of_tuples))
>
> This is beginning to feel clunky (but gives me essentially what I want),
> and I thought there was a better, more concise, way to achieve this, so
> I explored the new string format and format() function:
>
>>>> c = (1,3)
>>>> s = "{0[0]}"
>>>> print s.format(c)
> '1'
That's not actually the output copied and pasted. You have quotes around
the string, which you don't get if you pass it to the print command.
>>>> print format(c,s)
> Traceback (most recent call last):
> File "<interactive input>", line 1, in <module>
> ValueError: Invalid conversion specification
[...]
> Any idea why one form works and the other doesn't?
Because the format built-in function is not the same as the format string
method.
The string method takes brace substitutions, like "{0[0]}" which returns
the first item of the first argument.
The format function takes a format spec, not a brace substitution. For
example:
>>> format(c, '<10s')
'(1, 3) '
>>> format(c, '>10s')
' (1, 3)'
>>> format(c, '*>10s')
'****(1, 3)'
The details of the format spec are in the Fine Manual:
http://docs.python.org/library/string.html#formatspec
although sadly all the examples are about using brace substitutions, not
format specs.
(Personally, I find the documentation about format to be less than
helpful.)
You can also read the PEP that introduced the new formatting, but keep in
mind that there have been some changes since the PEP was written, so it
may not quite match the current status quo.
http://www.python.org/dev/peps/pep-3101/
--
Steven
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