Tools as Context-managers

Many marvin tools, e.g. Cube, or Maps, act as a means of accessing an underlying data-file. When data_origin == 'file', unless you delete the specific tool instance, the underlying file-handler will remain active. Therefore, if you expect to be creating many tool instances (by looping through a list of galaxies, for instance), you may create more open files than your system can handle. By using the tool as a context manager, the underlying data file is closed precisely when it is no longer relevant.

Any subclass of MarvinToolsClass can be used as a context manager. This includes the following tools:

The following example shows how to open a Cube as a context manager, but the same is true for any of the other tools.

>>> with Cube(filename='/Users/Brian/Work/Manga/redux/v2_3_1/8485/stack/manga-8485-1901-LOGCUBE.fits.gz') as cube:
>>>     # can access contents of file inside context
No.    Name      Ver    Type      Cards   Dimensions   Format
  0  PRIMARY       1 PrimaryHDU      75   ()
  1  FLUX          1 ImageHDU       100   (34, 34, 4563)   float32
 22  ICORREL       1 BinTableHDU     32   21213R x 5C   [J, J, J, J, D]
 23  ZCORREL       1 BinTableHDU     32   21458R x 5C   [J, J, J, J, D]

>>> # once context ceases to be active, the file is closed, and data are inaccessible
>>> cube.spectral_resolution
ValueError: I/O operation on closed file

While this can be inconvenient when acting on a single Cube, it can save you from having to manually close files when working with many Cubes in sequence, such as when running the same analysis on many Cubes in a loop.

>>> for plateifu in plateifus:
>>>     with Cube(plateifu) as cube:
>>>         cube_fit_stars_gas(l=cube.wave, f=cube.flux, w=cube.ivar)