How do I read and write files?

CIAO comes with a number of Python modules, including the pycrates module, and the I/O in Python page has more details.

As an example, we can filter an image just to read the filtered data, and then operate on the data values using NumPy methods:

import numpy as np
import pycrates  

cr = pycrates.read_file("img.fits[sky=circle(260, 2175, 60)]")
print(cr)

   Crate Type:        <IMAGECrate>
   Crate Name:        SENSITY
   Image Axes:        ['SKY', 'EQPOS']

ivals = pycrates.get_piximgvals(cr)
ngood = np.isfinite(ivals).sum()
print(f"Number of pixels: {ivals.size}   good: {ngood}")

print(f"Minimum:  {np.nanmin(ivals)}")
print(f"Maximum:  {np.nanmax(ivals)}")
print(f"Sum:      {np.nansum(ivals)}")

Number of pixels: 256   good: 247
Minimum:  0.0
Maximum:  9.246890158465249e-06
Sum:      0.00028823673187616805