On 3/16/2016 2:53 PM, Ben Finney wrote:
"the.gerenuk--- via Python-list" <python-list@python.org> writes:
The following error message, makes it a bit hard to understand what went wrong
"{:02}".format("1")
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
ValueError: '=' alignment not allowed in string format specifier
Meaning that the ‘str.format’ mini-language parser has decided on the
alignment specifier “=”. It's chosen that because:
Preceding the width field by a zero ('0') character enables
sign-aware zero-padding for numeric types. This is equivalent to a
fill character of '0' with an alignment type of '='.
<URL:https://docs.python.org/3/library/string.html#formatspec>
Nothing in the error message indicates why “'=' alignment” is relevant,
and it does not appear in the code.
Do you think some better error message should be used?
Yes, I think that error message needs to be improved. Please file a bug
report in Python's issue tracker <URL:https://bugs.python.org/>.
There already is a closed doc issue, which I am going to reopen to
further revise the doc. https://bugs.python.org/issue15660
For example a hint that "0" does work for the given argument.
I suggest: “zero-padding only allowed for numeric types, not 'str'”.
As someone else said, not true.
The problem with changing the exception message is that the formatter
does not know at the point of the exception whether the alignment was
set to '=' explicitly by the user or implicitly by the use of '0' fill.
--
Terry Jan Reedy
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