Use pooch.Decompress to load sample grids (#118)

The new pooch processor class removes the need for our custom
function that loads the xz compressed sample grids of global gravity,
geoid, and topography.

harmonica/datasets/sample_data.py

@@ -2,9 +2,6 @@
 Functions to load sample datasets used in the Harmonica docs.
 """
 import os
-import tempfile
-import lzma
-import shutil
 
 import xarray as xr
 import pandas as pd
@@ -42,8 +39,8 @@ def fetch_geoid_earth():
  The geoid grid (in meters). Coordinates are geodetic latitude and longitude.
 
  """
- fname = POOCH.fetch("geoid-earth-0.5deg.nc.xz")
- data = _load_xz_compressed_grid(fname, engine="scipy").astype("float64")
+ fname = POOCH.fetch("geoid-earth-0.5deg.nc.xz", processor=pooch.Decompress())
+ data = xr.open_dataset(fname, engine="scipy").astype("float64")
  return data
 
 
@@ -68,10 +65,10 @@ def fetch_gravity_earth():
  (``height_over_ell``). Coordinates are geodetic latitude and longitude.
 
  """
- fname = POOCH.fetch("gravity-earth-0.5deg.nc.xz")
+ fname = POOCH.fetch("gravity-earth-0.5deg.nc.xz", processor=pooch.Decompress())
  # The heights are stored as ints and data as float32 to save space on the data file.
  # Cast them to float64 to avoid integer division errors.
- data = _load_xz_compressed_grid(fname, engine="scipy").astype("float64")
+ data = xr.open_dataset(fname, engine="scipy").astype("float64")
  return data
 
 
@@ -98,10 +95,10 @@ def fetch_topography_earth():
  latitude and longitude.
 
  """
- fname = POOCH.fetch("etopo1-0.5deg.nc.xz")
+ fname = POOCH.fetch("etopo1-0.5deg.nc.xz", processor=pooch.Decompress())
  # The data are stored as int16 to save disk space. Cast them to floats to avoid
  # integer division problems when processing.
- data = _load_xz_compressed_grid(fname, engine="scipy").astype("float64")
+ data = xr.open_dataset(fname, engine="scipy").astype("float64")
  return data
 
 
@@ -172,25 +169,6 @@ def fetch_britain_magnetic():
  return pd.read_csv(POOCH.fetch("britain-magnetic.csv.xz"), compression="xz")
 
 
-def _load_xz_compressed_grid(fname, **kwargs):
- """
- Load a netCDF grid that has been xz compressed. Keyword arguments are passed to
- :func:`xarray.open_dataset`.
- """
- decompressed = tempfile.NamedTemporaryFile(suffix=".nc", delete=False)
- try:
- with decompressed:
- with lzma.open(fname, "rb") as compressed:
- shutil.copyfileobj(compressed, decompressed)
- # Call load to make sure the data are loaded into memory and not linked to file
- grid = xr.open_dataset(decompressed.name, **kwargs).load()
- # Close any files associated with this dataset to make sure can delete them
- grid.close()
- finally:
- os.remove(decompressed.name)
- return grid
-
-
 def fetch_south_africa_gravity():
  """
  Fetch gravity station data from South Africa