syn keyword pythonStatement     pass yield

syn match pythonStatement       '\s*\([.,]\)\@<!\<yield\>'

With current state it is matching whitespaces before yield. Do not recognizable if you have simple color theme, but if you have underline or bg(for pythonStatement) different from Normal - it will be noticeble.

And with new update we have
syn match pythonStetement '\s*[.,]\@<!\<yield\>'
Why do we even need this syn match beside syn keyword? Describe please.
If so i really think it should be something like this
syn match pythonStatement '\(\s*[.,]\)\@<!\<yield\>' But i'm still not sure why do we need this.