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# Tables

## `BinTableHDU`

class astropy.io.fits.BinTableHDU(data=None, header=None, name=None, uint=False, ver=None, character_as_bytes=False)

  Bases: `_TableBaseHDU`

  Binary table HDU class.

  Parameters:
    data `array`, `FITS_rec`, or `Table`

      Data to be used.

    header `Header`

      Header to be used.

    name `python:str`

      Name to be populated in `EXTNAME` keyword.

    uint bool, optional

      Set to `True` if the table contains unsigned integer columns.

    ver `python:int` > 0 or `python:None`, optional

      The ver of the HDU, will be the value of the keyword `EXTVER`. If not given or None, it defaults to the value of the `EXTVER` card of the `header` or 1. (default: None)

    character_as_bytes bool

      Whether to return bytes for string columns. By default this is `False` and (unicode) strings are returned, but this does not respect memory mapping and loads the whole column in memory when accessed.

  add_checksum(when=None, override_datasum=False, checksum_keyword='CHECKSUM', datasum_keyword='DATASUM')

    Add the `CHECKSUM` and `DATASUM` cards to this HDU with the values set to the checksum calculated for the HDU and the data respectively. The addition of the `DATASUM` card may be overridden.

    Parameters:
      when `python:str`, optional

        comment string for the cards; by default the comments will represent the time when the checksum was calculated

      override_datasum bool, optional

        add the `CHECKSUM` card only

      checksum_keyword `python:str`, optional

        The name of the header keyword to store the checksum value in; this is typically ‘CHECKSUM’ per convention, but there exist use cases in which a different keyword should be used

      datasum_keyword `python:str`, optional

        See `checksum_keyword`

    Notes

    For testing purposes, first call `add_datasum` with a `when` argument, then call `add_checksum` with a `when` argument and `override_datasum` set to `True`. This will provide consistent comments for both cards and enable the generation of a `CHECKSUM` card with a consistent value.

  add_datasum(when=None, datasum_keyword='DATASUM')

    Add the `DATASUM` card to this HDU with the value set to the checksum calculated for the data.

    Parameters:
      when `python:str`, optional

        Comment string for the card that by default represents the time when the checksum was calculated

      datasum_keyword `python:str`, optional

        The name of the header keyword to store the datasum value in; this is typically ‘DATASUM’ per convention, but there exist use cases in which a different keyword should be used

    Returns:
      checksum `python:int`

        The calculated datasum

    Notes

    For testing purposes, provide a `when` argument to enable the comment value in the card to remain consistent. This will enable the generation of a `CHECKSUM` card with a consistent value.

  property columns

    The `ColDefs` objects describing the columns in this table.

  copy()

    Make a copy of the table HDU, both header and data are copied.

  dump(datafile=None, cdfile=None, hfile=None, overwrite=False)

    Dump the table HDU to a file in ASCII format. The table may be dumped in three separate files, one containing column definitions, one containing header parameters, and one for table data.

    Parameters:
      datafile python:path-like object or python:file-like object, optional

        Output data file. The default is the root name of the fits file associated with this HDU appended with the extension `.txt`.

      cdfile python:path-like object or python:file-like object, optional

        Output column definitions file. The default is `None`, no column definitions output is produced.

      hfile python:path-like object or python:file-like object, optional

        Output header parameters file. The default is `None`, no header parameters output is produced.

      overwrite bool, optional

        If `True`, overwrite the output file if it exists. Raises an `OSError` if `False` and the output file exists. Default is `False`.

    Notes

    The primary use for the `dump` method is to allow viewing and editing the table data and parameters in a standard text editor. The `load` method can be used to create a new table from the three plain text (ASCII) files.

    - datafile: Each line of the data file represents one row of table data. The data is output one column at a time in column order. If a column contains an array, each element of the column array in the current row is output before moving on to the next column. Each row ends with a new line.

      Integer data is output right-justified in a 21-character field followed by a blank. Floating point data is output right justified using ‘g’ format in a 21-character field with 15 digits of precision, followed by a blank. String data that does not contain whitespace is output left-justified in a field whose width matches the width specified in the `TFORM` header parameter for the column, followed by a blank. When the string data contains whitespace characters, the string is enclosed in quotation marks (`""`). For the last data element in a row, the trailing blank in the field is replaced by a new line character.

      For column data containing variable length arrays (‘P’ format), the array data is preceded by the string `'VLA_Length= '` and the integer length of the array for that row, left-justified in a 21-character field, followed by a blank.

      Note

      This format does not support variable length arrays using the (‘Q’ format) due to difficult to overcome ambiguities. What this means is that this file format cannot support VLA columns in tables stored in files that are over 2 GB in size.

      For column data representing a bit field (‘X’ format), each bit value in the field is output right-justified in a 21-character field as 1 (for true) or 0 (for false).

    - cdfile: Each line of the column definitions file provides the definitions for one column in the table. The line is broken up into 8, sixteen-character fields. The first field provides the column name (`TTYPEn`). The second field provides the column format (`TFORMn`). The third field provides the display format (`TDISPn`). The fourth field provides the physical units (`TUNITn`). The fifth field provides the dimensions for a multidimensional array (`TDIMn`). The sixth field provides the value that signifies an undefined value (`TNULLn`). The seventh field provides the scale factor (`TSCALn`). The eighth field provides the offset value (`TZEROn`). A field value of `""` is used to represent the case where no value is provided.

    - hfile: Each line of the header parameters file provides the definition of a single HDU header card as represented by the card image.

  filebytes()

    Calculates and returns the number of bytes that this HDU will write to a file.

  fileinfo()

    Returns a dictionary detailing information about the locations of this HDU within any associated file. The values are only valid after a read or write of the associated file with no intervening changes to the `HDUList`.

    Returns:
      `python:dict` or `python:None`

        The dictionary details information about the locations of this HDU within an associated file. Returns `None` when the HDU is not associated with a file.

        Dictionary contents:

        Key | Value
        --- | ---
        file | File object associated with the HDU
        filemode | Mode in which the file was opened (readonly, copyonwrite, update, append, ostream)
        hdrLoc | Starting byte location of header in file
        datLoc | Starting byte location of data block in file
        datSpan | Data size including padding

  classmethod from_columns(columns, header=None, nrows=0, fill=False, character_as_bytes=False, **kwargs)

    Given either a `ColDefs` object, a sequence of `Column` objects, or another table HDU or table data (a `FITS_rec` or multi-field `numpy.ndarray` or `numpy.recarray` object, return a new table HDU of the class this method was called on using the column definition from the input.

    See also `FITS_rec.from_columns`.

    Parameters:
      columns python:sequence of `Column`, `ColDefs` astropy:-like

        The columns from which to create the table data, or an object with a column-like structure from which a `ColDefs` can be instantiated. This includes an existing `BinTableHDU` or `TableHDU`, or a `numpy.recarray` to give some examples.

        If these columns have data arrays attached that data may be used in initializing the new table. Otherwise the input columns will be used as a template for a new table with the requested number of rows.

      header `Header`

        An optional `Header` object to instantiate the new HDU yet. Header keywords specifically related to defining the table structure (such as the “TXXXn” keywords like TTYPEn) will be overridden by the supplied column definitions, but all other informational and data model-specific keywords are kept.

      nrows `python:int`

        Number of rows in the new table. If the input columns have data associated with them, the size of the largest input column is used. Otherwise the default is 0.

      fill bool

        If `True`, will fill all cells with zeros or blanks. If `False`, copy the data from input, undefined cells will still be filled with zeros/blanks.

      character_as_bytes bool

        Whether to return bytes for string columns when accessed from the HDU. By default this is `False` and (unicode) strings are returned, but for large tables this may use up a lot of memory.

    Notes

    Any additional keyword arguments accepted by the HDU class’s `__init__` may also be passed in as keyword arguments.

  classmethod fromstring(data, checksum=False, ignore_missing_end=False, **kwargs)

    Creates a new HDU object of the appropriate type from a string containing the HDU’s entire header and, optionally, its data.

    Note: When creating a new HDU from a string without a backing file object, the data of that HDU may be read-only. It depends on whether the underlying string was an immutable Python str/bytes object, or some kind of read-write memory buffer such as a `memoryview`.

    Parameters:
      data `python:str`, `bytearray`, `memoryview`, `ndarray`

        A byte string containing the HDU’s header and data.

      checksum bool, optional

        Check the HDU’s checksum and/or datasum.

      ignore_missing_end bool, optional

        Ignore a missing end card in the header data. Note that without the end card the end of the header may be ambiguous and resulted in a corrupt HDU. In this case the assumption is that the first 2880 block that does not begin with valid FITS header data is the beginning of the data.

      **kwargs optional

        May consist of additional keyword arguments specific to an HDU type–these correspond to keywords recognized by the constructors of different HDU classes such as `PrimaryHDU`, `ImageHDU`, or `BinTableHDU`. Any unrecognized keyword arguments are simply ignored.

  classmethod load(datafile, cdfile=None, hfile=None, replace=False, header=None)

    Create a table from the input ASCII files. The input is from up to three separate files, one containing column definitions, one containing header parameters, and one containing column data.

    The column definition and header parameters files are not required. When absent the column definitions and/or header parameters are taken from the header object given in the header argument; otherwise sensible defaults are inferred (though this mode is not recommended).

    Parameters:
      datafile python:path-like object or python:file-like object

        Input data file containing the table data in ASCII format.

      cdfile python:path-like object or python:file-like object, optional

        Input column definition file containing the names, formats, display formats, physical units, multidimensional array dimensions, undefined values, scale factors, and offsets associated with the columns in the table. If `None`, the column definitions are taken from the current values in this object.

      hfile python:path-like object or python:file-like object, optional

        Input parameter definition file containing the header parameter definitions to be associated with the table. If `None`, the header parameter definitions are taken from the current values in this objects header.

      replace bool, optional

        When `True`, indicates that the entire header should be replaced with the contents of the ASCII file instead of just updating the current header.

      header `Header`, optional

        When the cdfile and hfile are missing, use this Header object in the creation of the new table and HDU. Otherwise this Header supersedes the keywords from hfile, which is only used to update values not present in this Header, unless `replace=True` in which this Header’s values are completely replaced with the values from hfile.

    Notes

    The primary use for the `load` method is to allow the input of ASCII data that was edited in a standard text editor of the table data and parameters. The `dump` method can be used to create the initial ASCII files.

    - datafile: Each line of the data file represents one row of table data. The data is output one column at a time in column order. If a column contains an array, each element of the column array in the current row is output before moving on to the next column. Each row ends with a new line.

      Integer data is output right-justified in a 21-character field followed by a blank. Floating point data is output right justified using ‘g’ format in a 21-character field with 15 digits of precision, followed by a blank. String data that does not contain whitespace is output left-justified in a field whose width matches the width specified in the `TFORM` header parameter for the column, followed by a blank. When the string data contains whitespace characters, the string is enclosed in quotation marks (`""`). For the last data element in a row, the trailing blank in the field is replaced by a new line character.

      For column data containing variable length arrays (‘P’ format), the array data is preceded by the string `'VLA_Length= '` and the integer length of the array for that row, left-justified in a 21-character field, followed by a blank.

      Note

      This format does not support variable length arrays using the (‘Q’ format) due to difficult to overcome ambiguities. What this means is that this file format cannot support VLA columns in tables stored in files that are over 2 GB in size.

      For column data representing a bit field (‘X’ format), each bit value in the field is output right-justified in a 21-character field as 1 (for true) or 0 (for false).

    - cdfile: Each line of the column definitions file provides the definitions for one column in the table. The line is broken up into 8, sixteen-character fields. The first field provides the column name (`TTYPEn`). The second field provides the column format (`TFORMn`). The third field provides the display format (`TDISPn`). The fourth field provides the physical units (`TUNITn`). The fifth field provides the dimensions for a multidimensional array (`TDIMn`). The sixth field provides the value that signifies an undefined value (`TNULLn`). The seventh field provides the scale factor (`TSCALn`). The eighth field provides the offset value (`TZEROn`). A field value of `""` is used to represent the case where no value is provided.

    - hfile: Each line of the header parameters file provides the definition of a single HDU header card as represented by the card image.

  classmethod match_header(header)

    This is an abstract type that implements the shared functionality of the ASCII and Binary Table HDU types, which should be used instead of this.

  classmethod readfrom(fileobj, checksum=False, ignore_missing_end=False, **kwargs)

    Read the HDU from a file. Normally an HDU should be opened with `open()` which reads the entire HDU list in a FITS file. But this method is still provided for symmetry with `writeto()`.

    Parameters:
      fileobj python:file-like object

        Input FITS file. The file’s seek pointer is assumed to be at the beginning of the HDU.

      checksum bool

        If `True`, verifies that both `DATASUM` and `CHECKSUM` card values (when present in the HDU header) match the header and data of all HDU’s in the file.

      ignore_missing_end bool

        Do not issue an exception when opening a file that is missing an `END` card in the last header.

  req_cards(keyword, pos, test, fix_value, option, errlist)

    Check the existence, location, and value of a required `Card`.

    Parameters:
      keyword `python:str`

        The keyword to validate

      pos `python:int`, `python:callable()`

        If an `int`, this specifies the exact location this card should have in the header. Remember that Python is zero-indexed, so this means `pos=0` requires the card to be the first card in the header. If given a callable, it should take one argument–the actual position of the keyword–and return `True` or `False`. This can be used for custom evaluation. For example if `pos=lambda idx: idx > 10` this will check that the keyword’s index is greater than 10.

      test `python:callable()`

        This should be a callable (generally a function) that is passed the value of the given keyword and returns `True` or `False`. This can be used to validate the value associated with the given keyword.

      fix_value `python:str`, `python:int`, `python:float`, `complex`, bool, `python:None`

        A valid value for a FITS keyword to to use if the given `test` fails to replace an invalid value. In other words, this provides a default value to use as a replacement if the keyword’s current value is invalid. If `None`, there is no replacement value and the keyword is unfixable.

      option `python:str`

        Output verification option. Must be one of `"fix"`, `"silentfix"`, `"ignore"`, `"warn"`, or `"exception"`. May also be any combination of `"fix"` or `"silentfix"` with `"+ignore"`, `+warn`, or `+exception" (e.g. ``"fix+warn"`). See Verification Options for more info.

      errlist `python:list`

        A list of validation errors already found in the FITS file; this is used primarily for the validation system to collect errors across multiple HDUs and multiple calls to `req_cards`.

    Notes

    If `pos=None`, the card can be anywhere in the header. If the card does not exist, the new card will have the `fix_value` as its value when created. Also check the card’s value by using the `test` argument.

  run_option(option='warn', err_text='', fix_text='Fixed.', fix=None, fixable=True)

    Execute the verification with selected option.

  property size

    Size (in bytes) of the data portion of the HDU.

  update()

    Update header keywords to reflect recent changes of columns.

  verify(option='warn')

    Verify all values in the instance.

    Parameters:
      option `python:str`

        Output verification option. Must be one of `"fix"`, `"silentfix"`, `"ignore"`, `"warn"`, or `"exception"`. May also be any combination of `"fix"` or `"silentfix"` with `"+ignore"`, `"+warn"`, or `"+exception"` (e.g. `"fix+warn"`). See Verification Options for more info.

  verify_checksum()

    Verify that the value in the `CHECKSUM` keyword matches the value calculated for the current HDU CHECKSUM.

    Returns:
      valid `python:int`

        - 0 - failure

        - 1 - success

        - 2 - no `CHECKSUM` keyword present

  verify_datasum()

    Verify that the value in the `DATASUM` keyword matches the value calculated for the `DATASUM` of the current HDU data.

    Returns:
      valid `python:int`

        - 0 - failure

        - 1 - success

        - 2 - no `DATASUM` keyword present

  writeto(name, output_verify='exception', overwrite=False, checksum=False)

    Works similarly to the normal writeto(), but prepends a default `PrimaryHDU` are required by extension HDUs (which cannot stand on their own).

## `TableHDU`

class astropy.io.fits.TableHDU(data=None, header=None, name=None, ver=None, character_as_bytes=False)

  Bases: `_TableBaseHDU`

  FITS ASCII table extension HDU class.

  Parameters:
    data `array` or `FITS_rec`

      Data to be used.

    header `Header`

      Header to be used.

    name `python:str`

      Name to be populated in `EXTNAME` keyword.

    ver `python:int` > 0 or `python:None`, optional

      The ver of the HDU, will be the value of the keyword `EXTVER`. If not given or None, it defaults to the value of the `EXTVER` card of the `header` or 1. (default: None)

    character_as_bytes bool

      Whether to return bytes for string columns. By default this is `False` and (unicode) strings are returned, but this does not respect memory mapping and loads the whole column in memory when accessed.

  add_checksum(when=None, override_datasum=False, checksum_keyword='CHECKSUM', datasum_keyword='DATASUM')

    Add the `CHECKSUM` and `DATASUM` cards to this HDU with the values set to the checksum calculated for the HDU and the data respectively. The addition of the `DATASUM` card may be overridden.

    Parameters:
      when `python:str`, optional

        comment string for the cards; by default the comments will represent the time when the checksum was calculated

      override_datasum bool, optional

        add the `CHECKSUM` card only

      checksum_keyword `python:str`, optional

        The name of the header keyword to store the checksum value in; this is typically ‘CHECKSUM’ per convention, but there exist use cases in which a different keyword should be used

      datasum_keyword `python:str`, optional

        See `checksum_keyword`

    Notes

    For testing purposes, first call `add_datasum` with a `when` argument, then call `add_checksum` with a `when` argument and `override_datasum` set to `True`. This will provide consistent comments for both cards and enable the generation of a `CHECKSUM` card with a consistent value.

  add_datasum(when=None, datasum_keyword='DATASUM')

    Add the `DATASUM` card to this HDU with the value set to the checksum calculated for the data.

    Parameters:
      when `python:str`, optional

        Comment string for the card that by default represents the time when the checksum was calculated

      datasum_keyword `python:str`, optional

        The name of the header keyword to store the datasum value in; this is typically ‘DATASUM’ per convention, but there exist use cases in which a different keyword should be used

    Returns:
      checksum `python:int`

        The calculated datasum

    Notes

    For testing purposes, provide a `when` argument to enable the comment value in the card to remain consistent. This will enable the generation of a `CHECKSUM` card with a consistent value.

  property columns

    The `ColDefs` objects describing the columns in this table.

  copy()

    Make a copy of the table HDU, both header and data are copied.

  filebytes()

    Calculates and returns the number of bytes that this HDU will write to a file.

  fileinfo()

    Returns a dictionary detailing information about the locations of this HDU within any associated file. The values are only valid after a read or write of the associated file with no intervening changes to the `HDUList`.

    Returns:
      `python:dict` or `python:None`

        The dictionary details information about the locations of this HDU within an associated file. Returns `None` when the HDU is not associated with a file.

        Dictionary contents:

        Key | Value
        --- | ---
        file | File object associated with the HDU
        filemode | Mode in which the file was opened (readonly, copyonwrite, update, append, ostream)
        hdrLoc | Starting byte location of header in file
        datLoc | Starting byte location of data block in file
        datSpan | Data size including padding

  classmethod from_columns(columns, header=None, nrows=0, fill=False, character_as_bytes=False, **kwargs)

    Given either a `ColDefs` object, a sequence of `Column` objects, or another table HDU or table data (a `FITS_rec` or multi-field `numpy.ndarray` or `numpy.recarray` object, return a new table HDU of the class this method was called on using the column definition from the input.

    See also `FITS_rec.from_columns`.

    Parameters:
      columns python:sequence of `Column`, `ColDefs` astropy:-like

        The columns from which to create the table data, or an object with a column-like structure from which a `ColDefs` can be instantiated. This includes an existing `BinTableHDU` or `TableHDU`, or a `numpy.recarray` to give some examples.

        If these columns have data arrays attached that data may be used in initializing the new table. Otherwise the input columns will be used as a template for a new table with the requested number of rows.

      header `Header`

        An optional `Header` object to instantiate the new HDU yet. Header keywords specifically related to defining the table structure (such as the “TXXXn” keywords like TTYPEn) will be overridden by the supplied column definitions, but all other informational and data model-specific keywords are kept.

      nrows `python:int`

        Number of rows in the new table. If the input columns have data associated with them, the size of the largest input column is used. Otherwise the default is 0.

      fill bool

        If `True`, will fill all cells with zeros or blanks. If `False`, copy the data from input, undefined cells will still be filled with zeros/blanks.

      character_as_bytes bool

        Whether to return bytes for string columns when accessed from the HDU. By default this is `False` and (unicode) strings are returned, but for large tables this may use up a lot of memory.

    Notes

    Any additional keyword arguments accepted by the HDU class’s `__init__` may also be passed in as keyword arguments.

  classmethod fromstring(data, checksum=False, ignore_missing_end=False, **kwargs)

    Creates a new HDU object of the appropriate type from a string containing the HDU’s entire header and, optionally, its data.

    Note: When creating a new HDU from a string without a backing file object, the data of that HDU may be read-only. It depends on whether the underlying string was an immutable Python str/bytes object, or some kind of read-write memory buffer such as a `memoryview`.

    Parameters:
      data `python:str`, `bytearray`, `memoryview`, `ndarray`

        A byte string containing the HDU’s header and data.

      checksum bool, optional

        Check the HDU’s checksum and/or datasum.

      ignore_missing_end bool, optional

        Ignore a missing end card in the header data. Note that without the end card the end of the header may be ambiguous and resulted in a corrupt HDU. In this case the assumption is that the first 2880 block that does not begin with valid FITS header data is the beginning of the data.

      **kwargs optional

        May consist of additional keyword arguments specific to an HDU type–these correspond to keywords recognized by the constructors of different HDU classes such as `PrimaryHDU`, `ImageHDU`, or `BinTableHDU`. Any unrecognized keyword arguments are simply ignored.

  classmethod match_header(header)

    This is an abstract type that implements the shared functionality of the ASCII and Binary Table HDU types, which should be used instead of this.

  classmethod readfrom(fileobj, checksum=False, ignore_missing_end=False, **kwargs)

    Read the HDU from a file. Normally an HDU should be opened with `open()` which reads the entire HDU list in a FITS file. But this method is still provided for symmetry with `writeto()`.

    Parameters:
      fileobj python:file-like object

        Input FITS file. The file’s seek pointer is assumed to be at the beginning of the HDU.

      checksum bool

        If `True`, verifies that both `DATASUM` and `CHECKSUM` card values (when present in the HDU header) match the header and data of all HDU’s in the file.

      ignore_missing_end bool

        Do not issue an exception when opening a file that is missing an `END` card in the last header.

  req_cards(keyword, pos, test, fix_value, option, errlist)

    Check the existence, location, and value of a required `Card`.

    Parameters:
      keyword `python:str`

        The keyword to validate

      pos `python:int`, `python:callable()`

        If an `int`, this specifies the exact location this card should have in the header. Remember that Python is zero-indexed, so this means `pos=0` requires the card to be the first card in the header. If given a callable, it should take one argument–the actual position of the keyword–and return `True` or `False`. This can be used for custom evaluation. For example if `pos=lambda idx: idx > 10` this will check that the keyword’s index is greater than 10.

      test `python:callable()`

        This should be a callable (generally a function) that is passed the value of the given keyword and returns `True` or `False`. This can be used to validate the value associated with the given keyword.

      fix_value `python:str`, `python:int`, `python:float`, `complex`, bool, `python:None`

        A valid value for a FITS keyword to to use if the given `test` fails to replace an invalid value. In other words, this provides a default value to use as a replacement if the keyword’s current value is invalid. If `None`, there is no replacement value and the keyword is unfixable.

      option `python:str`

        Output verification option. Must be one of `"fix"`, `"silentfix"`, `"ignore"`, `"warn"`, or `"exception"`. May also be any combination of `"fix"` or `"silentfix"` with `"+ignore"`, `+warn`, or `+exception" (e.g. ``"fix+warn"`). See Verification Options for more info.

      errlist `python:list`

        A list of validation errors already found in the FITS file; this is used primarily for the validation system to collect errors across multiple HDUs and multiple calls to `req_cards`.

    Notes

    If `pos=None`, the card can be anywhere in the header. If the card does not exist, the new card will have the `fix_value` as its value when created. Also check the card’s value by using the `test` argument.

  run_option(option='warn', err_text='', fix_text='Fixed.', fix=None, fixable=True)

    Execute the verification with selected option.

  property size

    Size (in bytes) of the data portion of the HDU.

  update()

    Update header keywords to reflect recent changes of columns.

  verify(option='warn')

    Verify all values in the instance.

    Parameters:
      option `python:str`

        Output verification option. Must be one of `"fix"`, `"silentfix"`, `"ignore"`, `"warn"`, or `"exception"`. May also be any combination of `"fix"` or `"silentfix"` with `"+ignore"`, `"+warn"`, or `"+exception"` (e.g. `"fix+warn"`). See Verification Options for more info.

  verify_checksum()

    Verify that the value in the `CHECKSUM` keyword matches the value calculated for the current HDU CHECKSUM.

    Returns:
      valid `python:int`

        - 0 - failure

        - 1 - success

        - 2 - no `CHECKSUM` keyword present

  verify_datasum()

    Verify that the value in the `DATASUM` keyword matches the value calculated for the `DATASUM` of the current HDU data.

    Returns:
      valid `python:int`

        - 0 - failure

        - 1 - success

        - 2 - no `DATASUM` keyword present

  writeto(name, output_verify='exception', overwrite=False, checksum=False)

    Works similarly to the normal writeto(), but prepends a default `PrimaryHDU` are required by extension HDUs (which cannot stand on their own).

## `Column`

class astropy.io.fits.Column(name=None, format=None, unit=None, null=None, bscale=None, bzero=None, disp=None, start=None, dim=None, array=None, ascii=None, coord_type=None, coord_unit=None, coord_ref_point=None, coord_ref_value=None, coord_inc=None, time_ref_pos=None)

  Bases: `NotifierMixin`

  Class which contains the definition of one column, e.g. `ttype`, `tform`, etc. and the array containing values for the column.

  Construct a `Column` by specifying attributes. All attributes except `format` can be optional; see Column Creation and Creating an ASCII Table for more information regarding `TFORM` keyword.

  Parameters:
    name `python:str`, optional

      column name, corresponding to `TTYPE` keyword

    format `python:str`

      column format, corresponding to `TFORM` keyword

    unit `python:str`, optional

      column unit, corresponding to `TUNIT` keyword

    null `python:str`, optional

      null value, corresponding to `TNULL` keyword

    bscale int-like, optional

      bscale value, corresponding to `TSCAL` keyword

    bzero int-like, optional

      bzero value, corresponding to `TZERO` keyword

    disp `python:str`, optional

      display format, corresponding to `TDISP` keyword

    start `python:int`, optional

      column starting position (ASCII table only), corresponding to `TBCOL` keyword

    dim `python:str`, optional

      column dimension corresponding to `TDIM` keyword

    array python:iterable, optional

      a `list`, `numpy.ndarray` (or other iterable that can be used to initialize an ndarray) providing initial data for this column. The array will be automatically converted, if possible, to the data format of the column. In the case were non-trivial `bscale` and/or `bzero` arguments are given, the values in the array must be the physical values–that is, the values of column as if the scaling has already been applied (the array stored on the column object will then be converted back to its storage values).

    ascii bool, optional

      set `True` if this describes a column for an ASCII table; this may be required to disambiguate the column format

    coord_type `python:str`, optional

      coordinate/axis type corresponding to `TCTYP` keyword

    coord_unit `python:str`, optional

      coordinate/axis unit corresponding to `TCUNI` keyword

    coord_ref_point int-like, optional

      pixel coordinate of the reference point corresponding to `TCRPX` keyword

    coord_ref_value int-like, optional

      coordinate value at reference point corresponding to `TCRVL` keyword

    coord_inc int-like, optional

      coordinate increment at reference point corresponding to `TCDLT` keyword

    time_ref_pos `python:str`, optional

      reference position for a time coordinate column corresponding to `TRPOS` keyword

  property array

    The Numpy `ndarray` associated with this `Column`.

    If the column was instantiated with an array passed to the `array` argument, this will return that array. However, if the column is later added to a table, such as via `BinTableHDU.from_columns` as is typically the case, this attribute will be updated to reference the associated field in the table, which may no longer be the same array.

  property ascii

    Whether this `Column` represents a column in an ASCII table.

  copy()

    Return a copy of this `Column`.

## `ColDefs`

class astropy.io.fits.ColDefs(input, ascii=False)

  Bases: `NotifierMixin`

  Column definitions class.

  It has attributes corresponding to the `Column` attributes (e.g. `ColDefs` has the attribute `names` while `Column` has `name`). Each attribute in `ColDefs` is a list of corresponding attribute values from all `Column` objects.

  Parameters:
    input python:sequence of `Column` or `ColDefs` or `ndarray` or `recarray`

      An existing table HDU, an existing `ColDefs`, or any multi-field Numpy array or `numpy.recarray`.

    ascii bool

      Use True to ensure that ASCII table columns are used.

  add_col(column)

    Append one `Column` to the column definition.

  change_attrib(col_name, attrib, new_value)

    Change an attribute (in the `KEYWORD_ATTRIBUTES` list) of a `Column`.

    Parameters:
      col_name `python:str` or `python:int`

        The column name or index to change

      attrib `python:str`

        The attribute name

      new_value `object`

        The new value for the attribute

  change_name(col_name, new_name)

    Change a `Column`’s name.

    Parameters:
      col_name `python:str`

        The current name of the column

      new_name `python:str`

        The new name of the column

  change_unit(col_name, new_unit)

    Change a `Column`’s unit.

    Parameters:
      col_name `python:str` or `python:int`

        The column name or index

      new_unit `python:str`

        The new unit for the column

  del_col(col_name)

    Delete (the definition of) one `Column`.

    col_namestr or int

      The column’s name or index

  info(attrib='all', output=None)

    Get attribute(s) information of the column definition.

    Parameters:
      attrib `python:str`

        Can be one or more of the attributes listed in `astropy.io.fits.column.KEYWORD_ATTRIBUTES`. The default is `"all"` which will print out all attributes. It forgives plurals and blanks. If there are two or more attribute names, they must be separated by comma(s).

      output python:file-like object, optional

        File-like object to output to. Outputs to stdout by default. If `False`, returns the attributes as a `dict` instead.

    Notes

    This function doesn’t return anything by default; it just prints to stdout.

## `FITS_rec`

class astropy.io.fits.FITS_rec(input)

  Bases: `recarray`

  FITS record array class.

  `FITS_rec` is the data part of a table HDU’s data part. This is a layer over the `recarray`, so we can deal with scaled columns.

  It inherits all of the standard methods from `numpy.ndarray`.

  Construct a FITS record array from a recarray.

  property columns

    A user-visible accessor for the coldefs.

  copy(order='C')

    The Numpy documentation lies; `numpy.ndarray.copy` is not equivalent to `numpy.copy`. Differences include that it re-views the copied array as self’s ndarray subclass, as though it were taking a slice; this means `__array_finalize__` is called and the copy shares all the array attributes (including `._converted`!). So we need to make a deep copy of all those attributes so that the two arrays truly do not share any data.

  field(key)

    A view of a `Column`’s data as an array.

  property formats

    List of column FITS formats.

  classmethod from_columns(columns, nrows=0, fill=False, character_as_bytes=False)

    Given a `ColDefs` object of unknown origin, initialize a new `FITS_rec` object.

    Note

    This was originally part of the `new_table` function in the table module but was moved into a class method since most of its functionality always had more to do with initializing a `FITS_rec` object than anything else, and much of it also overlapped with `FITS_rec._scale_back`.

    Parameters:
      columns python:sequence of `Column` or `a` `ColDefs`

        The columns from which to create the table data. If these columns have data arrays attached that data may be used in initializing the new table. Otherwise the input columns will be used as a template for a new table with the requested number of rows.

      nrows `python:int`

        Number of rows in the new table. If the input columns have data associated with them, the size of the largest input column is used. Otherwise the default is 0.

      fill bool

        If `True`, will fill all cells with zeros or blanks. If `False`, copy the data from input, undefined cells will still be filled with zeros/blanks.

  property names

    List of column names.

  tolist()

    Return the array as an `a.ndim`-levels deep nested list of Python scalars.

    Return a copy of the array data as a (nested) Python list. Data items are converted to the nearest compatible builtin Python type, via the `item` function.

    If `a.ndim` is 0, then since the depth of the nested list is 0, it will not be a list at all, but a simple Python scalar.

    Parameters:
      none
    Returns:
      y `object`, or `python:list` of `object`, or `python:list` of `python:list` of `object`, or …

        The possibly nested list of array elements.

    Notes

    The array may be recreated via `a = np.array(a.tolist())`, although this may sometimes lose precision.

    Examples

    For a 1D array, `a.tolist()` is almost the same as `list(a)`, except that `tolist` changes numpy scalars to Python scalars:

        >>> a = np.uint32([1, 2])
        >>> a_list = list(a)
        >>> a_list
        [1, 2]
        >>> type(a_list[0])
        <class 'numpy.uint32'>
        >>> a_tolist = a.tolist()
        >>> a_tolist
        [1, 2]
        >>> type(a_tolist[0])
        <class 'int'>

    Additionally, for a 2D array, `tolist` applies recursively:

        >>> a = np.array([[1, 2], [3, 4]])
        >>> list(a)
        [array([1, 2]), array([3, 4])]
        >>> a.tolist()
        [[1, 2], [3, 4]]

    The base case for this recursion is a 0D array:

        >>> a = np.array(1)
        >>> list(a)
        Traceback (most recent call last):
          ...
        TypeError: iteration over a 0-d array
        >>> a.tolist()
        1

## `FITS_record`

class astropy.io.fits.FITS_record(input, row=0, start=None, end=None, step=None, base=None, **kwargs)

  Bases: `object`

  FITS record class.

  `FITS_record` is used to access records of the `FITS_rec` object. This will allow us to deal with scaled columns. It also handles conversion/scaling of columns in ASCII tables. The `FITS_record` class expects a `FITS_rec` object as input.

  Parameters:
    input `array`

      The array to wrap.

    row `python:int`, optional

      The starting logical row of the array.

    start `python:int`, optional

      The starting column in the row associated with this object. Used for subsetting the columns of the `FITS_rec` object.

    end `python:int`, optional

      The ending column in the row associated with this object. Used for subsetting the columns of the `FITS_rec` object.

  field(field)

    Get the field data of the record.

  setfield(field, value)

    Set the field data of the record.

## Table Functions

### `tabledump()`

astropy.io.fits.tabledump(filename, datafile=None, cdfile=None, hfile=None, ext=1, overwrite=False)

  Dump a table HDU to a file in ASCII format. The table may be dumped in three separate files, one containing column definitions, one containing header parameters, and one for table data.

  Parameters:
    filename python:path-like object or python:file-like object

      Input fits file.

    datafile python:path-like object or python:file-like object, optional

      Output data file. The default is the root name of the input fits file appended with an underscore, followed by the extension number (ext), followed by the extension `.txt`.

    cdfile python:path-like object or python:file-like object, optional

      Output column definitions file. The default is `None`, no column definitions output is produced.

    hfile python:path-like object or python:file-like object, optional

      Output header parameters file. The default is `None`, no header parameters output is produced.

    ext `python:int`

      The number of the extension containing the table HDU to be dumped.

    overwrite bool, optional

      If `True`, overwrite the output file if it exists. Raises an `OSError` if `False` and the output file exists. Default is `False`.

  Notes

  The primary use for the `tabledump` function is to allow editing in a standard text editor of the table data and parameters. The `tableload` function can be used to reassemble the table from the three ASCII files.

  - datafile: Each line of the data file represents one row of table data. The data is output one column at a time in column order. If a column contains an array, each element of the column array in the current row is output before moving on to the next column. Each row ends with a new line.

    Integer data is output right-justified in a 21-character field followed by a blank. Floating point data is output right justified using ‘g’ format in a 21-character field with 15 digits of precision, followed by a blank. String data that does not contain whitespace is output left-justified in a field whose width matches the width specified in the `TFORM` header parameter for the column, followed by a blank. When the string data contains whitespace characters, the string is enclosed in quotation marks (`""`). For the last data element in a row, the trailing blank in the field is replaced by a new line character.

    For column data containing variable length arrays (‘P’ format), the array data is preceded by the string `'VLA_Length= '` and the integer length of the array for that row, left-justified in a 21-character field, followed by a blank.

    Note

    This format does not support variable length arrays using the (‘Q’ format) due to difficult to overcome ambiguities. What this means is that this file format cannot support VLA columns in tables stored in files that are over 2 GB in size.

    For column data representing a bit field (‘X’ format), each bit value in the field is output right-justified in a 21-character field as 1 (for true) or 0 (for false).

  - cdfile: Each line of the column definitions file provides the definitions for one column in the table. The line is broken up into 8, sixteen-character fields. The first field provides the column name (`TTYPEn`). The second field provides the column format (`TFORMn`). The third field provides the display format (`TDISPn`). The fourth field provides the physical units (`TUNITn`). The fifth field provides the dimensions for a multidimensional array (`TDIMn`). The sixth field provides the value that signifies an undefined value (`TNULLn`). The seventh field provides the scale factor (`TSCALn`). The eighth field provides the offset value (`TZEROn`). A field value of `""` is used to represent the case where no value is provided.

  - hfile: Each line of the header parameters file provides the definition of a single HDU header card as represented by the card image.

### `tableload()`

astropy.io.fits.tableload(datafile, cdfile, hfile=None)

  Create a table from the input ASCII files. The input is from up to three separate files, one containing column definitions, one containing header parameters, and one containing column data. The header parameters file is not required. When the header parameters file is absent a minimal header is constructed.

  Parameters:
    datafile python:path-like object or python:file-like object

      Input data file containing the table data in ASCII format.

    cdfile python:path-like object or python:file-like object

      Input column definition file containing the names, formats, display formats, physical units, multidimensional array dimensions, undefined values, scale factors, and offsets associated with the columns in the table.

    hfile python:path-like object or python:file-like object, optional

      Input parameter definition file containing the header parameter definitions to be associated with the table. If `None`, a minimal header is constructed.

  Notes

  The primary use for the `tableload` function is to allow the input of ASCII data that was edited in a standard text editor of the table data and parameters. The tabledump function can be used to create the initial ASCII files.

  - datafile: Each line of the data file represents one row of table data. The data is output one column at a time in column order. If a column contains an array, each element of the column array in the current row is output before moving on to the next column. Each row ends with a new line.

    Integer data is output right-justified in a 21-character field followed by a blank. Floating point data is output right justified using ‘g’ format in a 21-character field with 15 digits of precision, followed by a blank. String data that does not contain whitespace is output left-justified in a field whose width matches the width specified in the `TFORM` header parameter for the column, followed by a blank. When the string data contains whitespace characters, the string is enclosed in quotation marks (`""`). For the last data element in a row, the trailing blank in the field is replaced by a new line character.

    For column data containing variable length arrays (‘P’ format), the array data is preceded by the string `'VLA_Length= '` and the integer length of the array for that row, left-justified in a 21-character field, followed by a blank.

    Note

    This format does not support variable length arrays using the (‘Q’ format) due to difficult to overcome ambiguities. What this means is that this file format cannot support VLA columns in tables stored in files that are over 2 GB in size.

    For column data representing a bit field (‘X’ format), each bit value in the field is output right-justified in a 21-character field as 1 (for true) or 0 (for false).

  - cdfile: Each line of the column definitions file provides the definitions for one column in the table. The line is broken up into 8, sixteen-character fields. The first field provides the column name (`TTYPEn`). The second field provides the column format (`TFORMn`). The third field provides the display format (`TDISPn`). The fourth field provides the physical units (`TUNITn`). The fifth field provides the dimensions for a multidimensional array (`TDIMn`). The sixth field provides the value that signifies an undefined value (`TNULLn`). The seventh field provides the scale factor (`TSCALn`). The eighth field provides the offset value (`TZEROn`). A field value of `""` is used to represent the case where no value is provided.

  - hfile: Each line of the header parameters file provides the definition of a single HDU header card as represented by the card image.

### `table_to_hdu()`

astropy.io.fits.table_to_hdu(table, character_as_bytes=False)

  Convert an `Table` object to a FITS `BinTableHDU`.

  Parameters:
    table `astropy.table.Table`

      The table to convert.

    character_as_bytes bool

      Whether to return bytes for string columns when accessed from the HDU. By default this is `False` and (unicode) strings are returned, but for large tables this may use up a lot of memory.

  Returns:
    table_hdu `BinTableHDU`

      The FITS binary table HDU.