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tutorial.py
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tutorial.py
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"""
Useful for:
* users learning xarray
* building tutorials in the documentation.
"""
import os
import pathlib
import numpy as np
from .backends.api import open_dataset as _open_dataset
from .backends.rasterio_ import open_rasterio as _open_rasterio
from .core.dataarray import DataArray
from .core.dataset import Dataset
_default_cache_dir_name = "xarray_tutorial_data"
base_url = "https://github.com/pydata/xarray-data"
version = "master"
def _construct_cache_dir(path):
import pooch
if isinstance(path, os.PathLike):
path = os.fspath(path)
elif path is None:
path = pooch.os_cache(_default_cache_dir_name)
return path
external_urls = {} # type: dict
external_rasterio_urls = {
"RGB.byte": "https://github.com/mapbox/rasterio/raw/1.2.1/tests/data/RGB.byte.tif",
"shade": "https://github.com/mapbox/rasterio/raw/1.2.1/tests/data/shade.tif",
}
file_formats = {
"air_temperature": 3,
"rasm": 3,
"ROMS_example": 4,
"tiny": 3,
"eraint_uvz": 3,
}
def _check_netcdf_engine_installed(name):
version = file_formats.get(name)
if version == 3:
try:
import scipy # noqa
except ImportError:
try:
import netCDF4 # noqa
except ImportError:
raise ImportError(
f"opening tutorial dataset {name} requires either scipy or "
"netCDF4 to be installed."
)
if version == 4:
try:
import h5netcdf # noqa
except ImportError:
try:
import netCDF4 # noqa
except ImportError:
raise ImportError(
f"opening tutorial dataset {name} requires either h5netcdf "
"or netCDF4 to be installed."
)
# idea borrowed from Seaborn
def open_dataset(
name,
cache=True,
cache_dir=None,
*,
engine=None,
**kws,
):
"""
Open a dataset from the online repository (requires internet).
If a local copy is found then always use that to avoid network traffic.
Available datasets:
* ``"air_temperature"``: NCEP reanalysis subset
* ``"rasm"``: Output of the Regional Arctic System Model (RASM)
* ``"ROMS_example"``: Regional Ocean Model System (ROMS) output
* ``"tiny"``: small synthetic dataset with a 1D data variable
* ``"era5-2mt-2019-03-uk.grib"``: ERA5 temperature data over the UK
* ``"eraint_uvz"``: data from ERA-Interim reanalysis, monthly averages of upper level data
Parameters
----------
name : str
Name of the file containing the dataset.
e.g. 'air_temperature'
cache_dir : path-like, optional
The directory in which to search for and write cached data.
cache : bool, optional
If True, then cache data locally for use on subsequent calls
**kws : dict, optional
Passed to xarray.open_dataset
See Also
--------
xarray.open_dataset
"""
try:
import pooch
except ImportError as e:
raise ImportError(
"tutorial.open_dataset depends on pooch to download and manage datasets."
" To proceed please install pooch."
) from e
logger = pooch.get_logger()
logger.setLevel("WARNING")
cache_dir = _construct_cache_dir(cache_dir)
if name in external_urls:
url = external_urls[name]
else:
path = pathlib.Path(name)
if not path.suffix:
# process the name
default_extension = ".nc"
if engine is None:
_check_netcdf_engine_installed(name)
path = path.with_suffix(default_extension)
elif path.suffix == ".grib":
if engine is None:
engine = "cfgrib"
url = f"{base_url}/raw/{version}/{path.name}"
# retrieve the file
filepath = pooch.retrieve(url=url, known_hash=None, path=cache_dir)
ds = _open_dataset(filepath, engine=engine, **kws)
if not cache:
ds = ds.load()
pathlib.Path(filepath).unlink()
return ds
def open_rasterio(
name,
engine=None,
cache=True,
cache_dir=None,
**kws,
):
"""
Open a rasterio dataset from the online repository (requires internet).
If a local copy is found then always use that to avoid network traffic.
Available datasets:
* ``"RGB.byte"``: TIFF file derived from USGS Landsat 7 ETM imagery.
* ``"shade"``: TIFF file derived from from USGS SRTM 90 data
``RGB.byte`` and ``shade`` are downloaded from the ``rasterio`` repository [1]_.
Parameters
----------
name : str
Name of the file containing the dataset.
e.g. 'RGB.byte'
cache_dir : path-like, optional
The directory in which to search for and write cached data.
cache : bool, optional
If True, then cache data locally for use on subsequent calls
**kws : dict, optional
Passed to xarray.open_rasterio
See Also
--------
xarray.open_rasterio
References
----------
.. [1] https://github.com/mapbox/rasterio
"""
try:
import pooch
except ImportError as e:
raise ImportError(
"tutorial.open_rasterio depends on pooch to download and manage datasets."
" To proceed please install pooch."
) from e
logger = pooch.get_logger()
logger.setLevel("WARNING")
cache_dir = _construct_cache_dir(cache_dir)
url = external_rasterio_urls.get(name)
if url is None:
raise ValueError(f"unknown rasterio dataset: {name}")
# retrieve the file
filepath = pooch.retrieve(url=url, known_hash=None, path=cache_dir)
arr = _open_rasterio(filepath, **kws)
if not cache:
arr = arr.load()
pathlib.Path(filepath).unlink()
return arr
def load_dataset(*args, **kwargs):
"""
Open, load into memory, and close a dataset from the online repository
(requires internet).
See Also
--------
open_dataset
"""
with open_dataset(*args, **kwargs) as ds:
return ds.load()
def scatter_example_dataset(*, seed=None) -> Dataset:
"""
Create an example dataset.
Parameters
----------
seed : int, optional
Seed for the random number generation.
"""
rng = np.random.default_rng(seed)
A = DataArray(
np.zeros([3, 11, 4, 4]),
dims=["x", "y", "z", "w"],
coords={
"x": np.arange(3),
"y": np.linspace(0, 1, 11),
"z": np.arange(4),
"w": 0.1 * rng.standard_normal(4),
},
)
B = 0.1 * A.x ** 2 + A.y ** 2.5 + 0.1 * A.z * A.w
A = -0.1 * A.x + A.y / (5 + A.z) + A.w
ds = Dataset({"A": A, "B": B})
ds["w"] = ["one", "two", "three", "five"]
ds.x.attrs["units"] = "xunits"
ds.y.attrs["units"] = "yunits"
ds.z.attrs["units"] = "zunits"
ds.w.attrs["units"] = "wunits"
ds.A.attrs["units"] = "Aunits"
ds.B.attrs["units"] = "Bunits"
return ds