python - Regex match even number of letters -

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i need match expression in python regular expressions matches number of letter occurrences. example:

 aaa        # no match aa         # match fsfaaaasdf # match safa       # match sdaaewasa  # match aeaia      # no match

an number of should match.

try regular expression:

^[^a]*((aa)+[^a]*)*$

and if as don’t need consecutive:

^[^a]*(a[^a]*a[^a]*)*$

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