You can copy files from external stages to internal stages in snowflake now: (without Python Stored Procedures)

COPY FILES INTO @[<namespace>.]<stage_name>[/<path>/]
  FROM @[<namespace>.]<stage_name>[/<path>/]
  [ FILES = ( '<file_name>' [ , '<file_name>' ] [ , ... ] ) ]
  [ PATTERN = '<regex_pattern>' ]
  [ DETAILED_OUTPUT = { TRUE | FALSE } ]

https://docs.snowflake.com/en/sql-reference/sql/copy-files