Terry J. Reedy added the comment:

'Enhancement' issues are for visible behavior additions (or occasionally, 
changes). This is intended to be an invisible small speedup, hence it is a 
'performance' issue, and gets a different title.

As explained in #17170, the change will not be a speedup if the substring being 
looked for is usually not there. The reason is the .find lookup and function 
call versus the direct syntax. Even if it is faster, I strongly doubt it would 
be hardly noticeable in the context of this function, which itself is a small 
piece of parsing an entire document, and it is against our policy to make such 
micro-optimizations in working code.

The complete block in question Lib/_markupbase.py, 254:7 is

  rawdata = self.rawdata
  if '>' in rawdata[j:]:
    return rawdata.find(">", j) + 1
  return -1

[Ugh. Localizing rawdata negates some of whatever advantage is gained from the 
double scan.]

If I were to rewrite it, I would replace it with

  try:
    return self.rawdata.index(">", j) + 1
  except ValueError:
    return -1

as better style, and a better example for readers, regardless of micro speed 
differences. But style-only changes in working code is also against our policy. 
So I would be closing this if Ezio had not grabbed it ;-).

----------
nosy: +terry.reedy

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<http://bugs.python.org/issue17183>
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