PrimaryHDU¶
- class pyfits.PrimaryHDU(data=None, header=None, do_not_scale_image_data=False, uint=False)¶
Bases: pyfits.hdu.image._ImageBaseHDU
FITS primary HDU class.
Construct a primary HDU.
Parameters: data : array or DELAYED, optional
The data in the HDU.
header : Header instance, optional
do_not_scale_image_data : bool, optional
If True, image data is not scaled using BSCALE/BZERO values when read.
uint : bool, optional
Interpret signed integer data where BZERO is the central value and BSCALE == 1 as unsigned integer data. For example, int16 data with BZERO = 32768 and BSCALE = 1 would be treated as uint16 data.
- add_checksum(when=None, override_datasum=False, blocking='standard')¶
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 : 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
blocking: str, optional :
“standard” or “nonstandard”, compute sum 2880 bytes at a time, or not
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, blocking='standard')¶
Add the DATASUM card to this HDU with the value set to the checksum calculated for the data.
Parameters: when : str, optional
Comment string for the card that by default represents the time when the checksum was calculated
blocking: str, optional :
“standard” or “nonstandard”, compute sum 2880 bytes at a time, or not
Returns: checksum : 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.
- copy()¶
Make a copy of the HDU, both header and data are copied.
- filebytes()¶
Calculates and returns the number of bytes that this HDU will write to a file.
Parameters: None : Returns: Number of bytes :
- 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.
Parameters: None :
Returns: dictionary or 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 fromstring(data, fileobj=None, offset=0, 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.
Parameters: data : str
A byte string contining the HDU’s header and, optionally, its data. If fileobj is not specified, and the length of data extends beyond the header, then the trailing data is taken to be the HDU’s data. If fileobj is specified then the trailing data is ignored.
fileobj : file, optional
The file-like object that this HDU was read from.
offset : int, optional
If fileobj is specified, the offset into the file-like object at which this HDU begins.
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 can’t be found, so the entire data is just assumed to be the header.
kwargs : optional
May contain additional keyword arguments specific to an HDU type. Any unrecognized kwargs are simply ignored.
- classmethod match_header(header)¶
- classmethod readfrom(fileobj, checksum=False, ignore_missing_end=False, **kwargs)¶
Read the HDU from a file. Normally an HDU should be opened with fitsopen() which reads the entire HDU list in a FITS file. But this method is still provided for symmetry with writeto().
Parameters: fileobj : file object or 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.
- classmethod register_hdu(hducls)¶
- req_cards(keyword, pos, test, fix_value, option, errlist)¶
Check the existence, location, and value of a required Card.
TODO: Write about parameters
If pos = None, it can be anywhere. 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.
- scale(type=None, option='old', bscale=1, bzero=0)¶
Scale image data by using BSCALE/BZERO.
Call to this method will scale data and update the keywords of BSCALE and BZERO in _header. This method should only be used right before writing to the output file, as the data will be scaled and is therefore not very usable after the call.
Parameters: type : str, optional
destination data type, use a string representing a numpy dtype name, (e.g. 'uint8', 'int16', 'float32' etc.). If is None, use the current data type.
option : str
How to scale the data: if "old", use the original BSCALE and BZERO values when the data was read/created. If "minmax", use the minimum and maximum of the data to scale. The option will be overwritten by any user specified bscale/bzero values.
bscale, bzero : int, optional
User-specified BSCALE and BZERO values.
- size()¶
Size (in bytes) of the data portion of the HDU.
- classmethod unregister_hdu(hducls)¶
- update_ext_name(value, comment=None, before=None, after=None, savecomment=False)¶
Update the extension name associated with the HDU.
If the keyword already exists in the Header, it’s value and/or comment will be updated. If it does not exist, a new card will be created and it will be placed before or after the specified location. If no before or after is specified, it will be appended at the end.
Parameters: value : str
value to be used for the new extension name
comment : str, optional
to be used for updating, default=None.
before : str or int, optional
name of the keyword, or index of the Card before which the new card will be placed in the Header. The argument before takes precedence over after if both specified.
after : str or int, optional
name of the keyword, or index of the Card after which the new card will be placed in the Header.
savecomment : bool, optional
When True, preserve the current comment for an existing keyword. The argument savecomment takes precedence over comment if both specified. If comment is not specified then the current comment will automatically be preserved.
- update_ext_version(value, comment=None, before=None, after=None, savecomment=False)¶
Update the extension version associated with the HDU.
If the keyword already exists in the Header, it’s value and/or comment will be updated. If it does not exist, a new card will be created and it will be placed before or after the specified location. If no before or after is specified, it will be appended at the end.
Parameters: value : str
value to be used for the new extension version
comment : str, optional
to be used for updating, default=None.
before : str or int, optional
name of the keyword, or index of the Card before which the new card will be placed in the Header. The argument before takes precedence over after if both specified.
after : str or int, optional
name of the keyword, or index of the Card after which the new card will be placed in the Header.
savecomment : bool, optional
When True, preserve the current comment for an existing keyword. The argument savecomment takes precedence over comment if both specified. If comment is not specified then the current comment will automatically be preserved.
- update_header()¶
- verify(option='warn')¶
Verify all values in the instance.
Parameters: option : str
Output verification option. Must be one of "fix", "silentfix", "ignore", "warn", or "exception". See Verification options for more info.
- verify_checksum(blocking='standard')¶
Verify that the value in the CHECKSUM keyword matches the value calculated for the current HDU CHECKSUM.
- blocking: str, optional
- “standard” or “nonstandard”, compute sum 2880 bytes at a time, or not
Returns: valid : int
- 0 - failure
- 1 - success
- 2 - no CHECKSUM keyword present
- verify_datasum(blocking='standard')¶
Verify that the value in the DATASUM keyword matches the value calculated for the DATASUM of the current HDU data.
- blocking: str, optional
- “standard” or “nonstandard”, compute sum 2880 bytes at a time, or not
Returns: valid : int
- 0 - failure
- 1 - success
- 2 - no DATASUM keyword present
- writeto(*args, **kwargs)¶
Write the HDU to a new file. This is a convenience method to provide a user easier output interface if only one HDU needs to be written to a file.
Parameters: name : file path, file object or file-like object
Output FITS file. If opened, must be opened for append (“ab+”)).
output_verify : str
Output verification option. Must be one of "fix", "silentfix", "ignore", "warn", or "exception". See Verification options for more info.
clobber : bool
Overwrite the output file if exists.
classExtensions : dict
A dictionary that maps pyfits classes to extensions of those classes. When present in the dictionary, the extension class will be constructed in place of the pyfits class.
checksum : bool
When True adds both DATASUM and CHECKSUM cards to the header of the HDU when written to the file.
- ImgCode = {'uint64': 64, 'uint16': 16, 'int16': 16, 'int64': 64, 'int32': 32, 'float64': -64, 'uint8': 8, 'float32': -32, 'uint32': 32}¶
- NumCode = {-64: 'float64', -32: 'float32', 32: 'int32', 8: 'uint8', 64: 'int64', 16: 'int16'}¶
- data¶
Works similarly to property(), but computes the value only once.
Adapted from the recipe at http://code.activestate.com/recipes/363602-lazy-property-evaluation
- header¶
- is_image¶
- name¶
- section¶
Access a section of the image array without loading the entire array into memory. The Section object returned by this attribute is not meant to be used directly by itself. Rather, slices of the section return the appropriate slice of the data, and loads only that section into memory.
Sections are mostly obsoleted by memmap support, but should still be used to deal with very large scaled images. See the Data Sections section of the PyFITS documentation for more details.
- shape¶
Shape of the image array–should be equivalent to self.data.shape.
- standard_keyword_comments = {'BITPIX': 'array data type', 'XTENSION': 'Image extension', 'SIMPLE': 'conforms to FITS standard', 'NAXIS': 'number of array dimensions', 'PCOUNT': 'number of parameters', 'GROUPS': 'has groups', 'GCOUNT': 'number of groups'}¶