Terry J. Reedy added the comment: As I read the docs, the error message is correct and this issue is invalid as a behavior issue. I read the OP's second message as more or less saying this also. "'=' Forces the padding to be placed after the sign (if any) but before the digits. This is used for printing fields in the form ‘+000000120’. This alignment option is only valid for numeric types." "If the width field is preceded by a zero ('0') character, this enables zero-padding. This is equivalent to an alignment type of '=' and a fill character of '0'." So ":02" is equivalent to ":0=2", which is invalid.

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'{:02d}'.format(1) '01' works fine.

I decided make this a doc issue and add " for numeric types" after "this enables zero-padding" before closing this. ---------- assignee: -> docs@python components: +Documentation -Interpreter Core nosy: +docs@python, terry.reedy versions: +Python 2.7, Python 3.3 _______________________________________ Python tracker <report@bugs.python.org> <http://bugs.python.org/issue15660> _______________________________________