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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def build(self, region=None, profile=None):
 """Get or create the provider for the given region and profile."""


        with self.lock:
            # memoization lookup key derived from region + profile.
            key = "{}-{}".format(profile, region)
            try:
                # assume provider is in provider dictionary.
                provider = self.providers[key]
            except KeyError:
                msg = "Missed memoized lookup ({}), creating new AWS Provider."
                logger.debug(msg.format(key))
                if not region:
                    region = self.region
                # memoize the result for later.
                self.providers[key] = Provider(
                    get_session(region=region, profile=profile),
                    region=region,
                    **self.kwargs
                )
                provider = self.providers[key]

        return provider