How to slice and loop through a netCDF variable in Python?

Question

I have a netCDF variable with 372 time-steps, I need to slice this variable to read in each individual time-step for subsequent processing.

I have used glob. to read in my 12 netCDF files and then defined the variables.

 NAME_files = glob.glob('RGL*nc') NAME_files = NAME_files[0:12] for n in (NAME_files): RGL = Dataset(n, mode='r') footprint = RGL.variables['fp'][:] lons = RGL.variables['lon'][:] lats = RGL.variables['lat'][:] 

I now need to repeat the code below in a loop for each of the 372 time-steps of the variable 'footprint'.

 footprint_2 = RGL.variables['fp'][:,:,1:2] 

I'm new to Python and have a poor grasp of looping. Any help would be appreciated, including better explanation/description of my issue.

Answer 1

You need to determine both the dimensions and shape of the fp variable in order to access it properly.

I'm making assumptions here about those values.

Your code implies 3 dimensions: time,lon,lat. Again just assuming.

footprint_2 =  RGL.variables['fp'][:,:,1:2]

But the code above gets all the times, all the lons, for 1 latitude. Slice 1:2 selects 1 value.

fp_dims = RGL.variables['fp'].dimensions
print(fp_dims)
# a tuple of dimesions names
 (u'time', u'lon', u'lat')

fp_shape = RGL.variables['fp'].shape

# a tuple of dimesions sizes or lengths
print(fp_shape)
 (372, 30, 30)

len = fp_shape[0]

for time_idx in range(0,len)):
  # you don't say if you want a single lon,lat or all the lon,lat's for a given time step.
  test = RGL.variables['fp'][time_idx,:,:]
  # or if you really want this:
  test = RGL.variables['fp'][time_idx,:,1:2]
  # or a single lon, lat
  test = RGL.variables['fp'][time_idx,8,8]