[Python-Dev] transitioning from % to {} formatting (original) (raw)

Georg Brandl g.brandl at gmx.net
Sat Oct 3 11:22:04 CEST 2009

Bugbee, Larry schrieb:

Do the users get any say in this?

I'm a user! :-) I hate calling methods on string literals, I think it looks very odd to have code like this: "Displaying {0} of {1} revisions".format(x, y) Ugh! Good point. Is Python to be an easy-to-learn-and-remember language? I submit we are losing that one. To a user, this will be confusing. To a C programmer coming over to Python, especially so. Some of what makes %-formatting easy to remember is its parallel in C.

To a .NET programmer coming to Python (think IronPython), %-formatting will be strange, while {}-style formatting will be familiar. I don't know how many programmers come to Python from C nowadays.

I also think that we are merely so accustomed to "..." % bar that we never think about new users who go "Huh? String modulo string?" -- why should that initial discomfort be less than that of calling a method on a literal?

Being able to call a method on literals is simply consistent; literals are objects as well as an object referred to by a name. There are languages where you can't even call foo[bar].baz() because method calls only work on single names. I call that ugly.

I'm conflicted. Philosophically I like the idea of mnemonic names over positional variables and allowing variable values determined elsewhere to be inserted in print strings. It is appealing.

Unless the benefit is at least 2x, a change should not be made,

I don't see how numbers like "2x" can be applied when measuring the benefit of a language feature.

and I don't think this benefit rises to where it is worth the confusion and problems. ...and converting the legacy base. And forget pretty, not that %-formatting is pretty either. Besides, according to the bench, it is slower too. And it will take editors a while before the new syntax is supported and colorized, thus some errors for a while.

This is no different from all other language features. Some editors I encountered do not yet color the with statement. Should I therefore refrain from using it?

Highlighting formatting placeholders in string literals is questionable anyway, since a highlighter has no way of knowing whether a given string literal will be used for formatting.

....and if one wants a "{" or a "}" in the printed output, one has to escape it? That is -2x over wanting a "%" in the output.

Again a number. Where does it come from?

Georg

-- Thus spake the Lord: Thou shalt indent with four spaces. No more, no less. Four shall be the number of spaces thou shalt indent, and the number of thy indenting shall be four. Eight shalt thou not indent, nor either indent thou two, excepting that thou then proceed to four. Tabs are right out.

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