The File Module (gdt.core.file)

Introduction

The File module contains, of primary importance, the FitsFileContextManager abstract class. As the name suggests, it is a context manager for accessing FITS files. While this class is intended to be inherited, we can demonstrate how this class works and is intended to be used.

Examples

Let’s assume we have the FITS file “glg_ctime_nb_bn120415958_v00.pha” in our current directory. You can access it with the following:

>>> from gdt.core import data_path
>>> from gdt.core.file import FitsFileContextManager
>>> filepath = data_path.joinpath('fermi-gbm').joinpath("glg_ctime_nb_bn120415958_v00.pha")
>>> f = FitsFileContextManager.open(filepath)
>>> f
<FitsFileContextManager(filename="glg_ctime_nb_bn120415958_v00.pha") at 0x109d25410>

The object contains some convenience functions:

>>> # number of HDUs
>>> f.num_hdus
4

>>> # get the column names in the second HDU (zero-indexed)
>>> f.get_column_names(2)
('COUNTS', 'EXPOSURE', 'QUALITY', 'TIME', 'ENDTIME')

>>> # retrieve the 'EXPOSURE' column
>>> f.column(2, 'EXPOSURE')
array([0.25506625, 0.25459924, 0.25496757, ..., 0.2551209 , 0.25507143,
       0.25600004], dtype=float32)

>>> # retrieve both the 'TIME' and 'ENDTIME' columns in a single array
>>> f.columns_as_array(2, ['TIME', 'ENDTIME'])
array([[3.56222662e+08, 3.56222662e+08],
       [3.56222662e+08, 3.56222662e+08],
       [3.56222662e+08, 3.56222663e+08],
       ...,
       [3.56224561e+08, 3.56224561e+08],
       [3.56224561e+08, 3.56224562e+08],
       [3.56224562e+08, 3.56224562e+08]])

The underlying Astropy HDUList can be accessed directly:

>>> f.hdulist
<astropy.io.fits.hdu.image.PrimaryHDU object at 0x103d31dd0>,
<astropy.io.fits.hdu.table.BinTableHDU object at 0x108b294d0>,
<astropy.io.fits.hdu.table.BinTableHDU object at 0x108af4810>,
<astropy.io.fits.hdu.table.BinTableHDU object at 0x108b300d0>]

Whenever we access the file this way, we must remember to close it:

>>> f.close()

The power behind using a context manager is that we can open the file in a with block and the file is closed properly when we exit the block or hit an error:

>>> with FitsFileContextManager(filepath) as f:
>>>     times = f.column(2, 'TIME')
>>>
>>> print(times)
array([3.56222662e+08, 3.56222662e+08, 3.56222662e+08, ...,
       3.56224561e+08, 3.56224561e+08, 3.56224562e+08])

Reference/API

gdt.core.file Module

Classes

FileContextManager(file_path[, mode])
FitsFileContextManager()	A context manager for FITS files.

Class Inheritance Diagram