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# open

asdf.open(fd, uri=None, mode=None, validate_checksums=False, extensions=None, ignore_version_mismatch=True, ignore_unrecognized_tag=False, _force_raw_types=False, copy_arrays=False, memmap=NotSet, lazy_load=True, custom_schema=None, strict_extension_check=False, ignore_missing_extensions=False, _get_yaml_content=False)

  Open an existing ASDF file.

  Parameters:
    fd string or file-like object

      May be a string `file` or `http` URI, or a Python file-like object.

    uri string, optional

      The URI of the file. Only required if the URI can not be automatically determined from `fd`.

    mode string, optional

      The mode to open the file in. Must be `r` (default) or `rw`.

    validate_checksums bool, optional

      If `True`, validate the blocks against their checksums. Requires reading the entire file, so disabled by default.

    extensions object, optional

      Additional extensions to use when reading and writing the file. May be an `asdf.extension.Extension` or a `list` of extensions.

    ignore_version_mismatch bool, optional

      When `True`, do not raise warnings for mismatched schema versions. Set to `True` by default.

    ignore_unrecognized_tag bool, optional

      When `True`, do not raise warnings for unrecognized tags. Set to `False` by default.

    copy_arrays bool, optional

      When `False`, when reading files, attempt to memmap underlying data arrays when possible.

    memmap bool, optional

      When `True`, when reading files, attempt to memmap underlying data arrays when possible. When set, this argument will override `copy_arrays`. When not set, the `copy_arrays` will determine if arrays are memory mapped or copied. `copy_arrays` will be deprecated and the default will change in an upcoming asdf version which by default will not memory map arrays.

    lazy_load bool, optional

      When `True` and the underlying file handle is seekable, data arrays will only be loaded lazily: i.e. when they are accessed for the first time. In this case the underlying file must stay open during the lifetime of the tree. Setting to False causes all data arrays to be loaded up front, which means that they can be accessed even after the underlying file is closed. Note: even if `lazy_load` is `False`, `memmap` is still taken into account.

    custom_schema str, optional

      Path to a custom schema file that will be used for a secondary validation pass. This can be used to ensure that particular ASDF files follow custom conventions beyond those enforced by the standard.

    strict_extension_check bool, optional

      When `True`, if the given ASDF file contains metadata about the extensions used to create it, and if those extensions are not installed, opening the file will fail. When `False`, opening a file under such conditions will cause only a warning. Defaults to `False`.

    ignore_missing_extensions bool, optional

      When `True`, do not raise warnings when a file is read that contains metadata about extensions that are not available. Defaults to `False`.

  Returns:
    asdffile AsdfFile

      The new AsdfFile object.