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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 select_bucket_region(custom_bucket, hook_region, stacker_bucket_region, provider_region):
 """Returns the appropriate region to use when uploading functions. Select the appropriate region for the bucket where lambdas are uploaded in. Args: custom_bucket (str, None):
 The custom bucket name provided by the `bucket` kwarg of the aws_lambda hook, if provided. hook_region (str):
 The contents of the `bucket_region` argument to the hook. stacker_bucket_region (str):
 The contents of the `stacker_bucket_region` global setting. provider_region (str):
 The region being used by the provider. Returns: str: The appropriate region string. """

    region = None
    if custom_bucket:
        region = hook_region
    else:
        region = stacker_bucket_region
    return region or provider_region