On 2/22/2011 6:28 PM, Steve Holden wrote:
On Feb 22, 2011, at 3:08 PM, Eric Smith wrote:
Quoting PEP 3101:
An example of the 'getitem' syntax:
"My name is {0[name]}".format(dict(name='Fred'))
It should be noted that the use of 'getitem' within a format string
is much more limited than its conventional usage. In the above example,
the string 'name' really is the literal string 'name', not a variable
named 'name'. The rules for parsing an item key are very simple.
If it starts with a digit, then it is treated as a number, otherwise
it is used as a string.
That's not strictly true:
d = {"Steve":"Holden", "Guido":"van Rossum", 21.2:"float"}
d[21.1]
Traceback (most recent call last):
File "<stdin>", line 1, in<module>
KeyError: 21.1
d[21.2]
'float'
"{0[21.2]}".format(d)
Traceback (most recent call last):
File "<stdin>", line 1, in<module>
KeyError: '21.2'
You are correct, I didn't exactly implement the PEP on this point,
probably as a shortcut. I think there's an issue somewhere that
discusses this, but I can't find it. The CPython implementation is
really using "If every character is a digit, then it is treated as an
integer, otherwise it is used as a string".
See find_name_split in Objects/stringlib/string_format.h, in particular
the call to get_integer() and the interpretation of the result.
Eric.
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