[issue27078] Make f'' strings faster than .format: BUILD_STRING opcode?

[Eric V. Smith]

Eric V. Smith added the comment:

> And the expected performance for optimal `f'X is {x}'` code would 
> be *faster* than `"'X is %s' % (x,)"` which still needs to 
> interpret the string at runtime, and build a proper tuple object 
> on stack.

That's not necessarily true. The f-string version still needs to invoke the .format() method on the object, instead of only working for a handful of hard-coded types.

I'm not saying there aren't optimization opportunities, but it may be that %-formatting is always faster.

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<http://bugs.python.org/issue27078>
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