Working with the PAVICS THREDDS server

# Define some useful variables for following steps
import os

PAVICS_HOST = os.getenv("PAVICS_HOST", "pavics.ouranos.ca")
if PAVICS_HOST == "":
    raise ValueError("Invalid PAVICS HOST value.")

THREDDS_URL = f"https://{PAVICS_HOST}/twitcher/ows/proxy/thredds"
print("THREDDS URL:", THREDDS_URL)

THREDDS URL: https://pavics.ouranos.ca/twitcher/ows/proxy/thredds

# NBVAL_IGNORE_OUTPUT

import xarray as xr

PUBLIC_URL = f"{THREDDS_URL}/dodsC/birdhouse/testdata/ta_Amon_MRI-CGCM3_decadal1980_r1i1p1_199101-200012.nc"
ds = xr.open_dataset(PUBLIC_URL)
ds

<xarray.Dataset> Size: 565MB
Dimensions:    (time: 120, bnds: 2, lat: 160, lon: 320, plev: 23)
Coordinates:
  * time       (time) datetime64[ns] 960B 1991-01-16T12:00:00 ... 2000-12-16T...
  * lat        (lat) float64 1kB -89.14 -88.03 -86.91 ... 86.91 88.03 89.14
  * lon        (lon) float64 3kB 0.0 1.125 2.25 3.375 ... 356.6 357.8 358.9
  * plev       (plev) float64 184B 1e+05 9.25e+04 8.5e+04 ... 200.0 100.0 40.0
Dimensions without coordinates: bnds
Data variables:
    time_bnds  (time, bnds) datetime64[ns] 2kB ...
    lat_bnds   (lat, bnds) float64 3kB ...
    lon_bnds   (lon, bnds) float64 5kB ...
    ta         (time, plev, lat, lon) float32 565MB ...
Attributes: (12/28)
    institution:                     MRI (Meteorological Research Institute, ...
    institute_id:                    MRI
    experiment_id:                   decadal1980
    source:                          MRI-CGCM3 2011 atmosphere: GSMUV (gsmuv-...
    model_id:                        MRI-CGCM3
    forcing:                         GHG, SA, Oz, LU, Sl, Vl, BC, OC (GHG inc...
    ...                              ...
    title:                           MRI-CGCM3 model output prepared for CMIP...
    parent_experiment:               N/A
    modeling_realm:                  atmos
    realization:                     1
    cmor_version:                    2.7.1
    DODS_EXTRA.Unlimited_Dimension:  time

# NBVAL_IGNORE_OUTPUT

from webob.exc import HTTPError

SECURED_URL = f"{THREDDS_URL}/dodsC/birdhouse/testdata/secure/tasmax_Amon_MPI-ESM-MR_rcp45_r2i1p1_200601-200612.nc"
try:
    ds = xr.open_dataset(SECURED_URL, decode_cf=False)
# depending on 'xarray' version, different errors are raised when failing authentication according to how they handle it
except OSError as exc:
    # "NetCDF: Access failure" xarray >= 0.20
    # "Authorization failure" xarray < 0.17
    assert "NetCDF: Access failure" in str(exc) or "Authorization failure" in str(exc)
except HTTPError as exc:  # xarray >= 0.17
    # note: raised error is 500 with 'message' Unauthorized instead of directly raising HTTPUnauthorized
    assert "401 Unauthorized" in str(exc)
else:
    raise RuntimeError(
        "Expected unauthorized response, but dataset open operation did not raise!"
    )

print("Unauthorized was raised as expected.")

Unauthorized was raised as expected.

syntax error, unexpected WORD_WORD, expecting SCAN_ATTR or SCAN_DATASET or SCAN_ERROR
context: <?xml^ version="1.0" encoding="utf-8"?><ExceptionReport version="1.0.0" xmlns="http://www.opengis.net/ows/1.1" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.opengis.net/ows/1.1 http://schemas.opengis.net/ows/1.1.0/owsExceptionReport.xsd"> <Exception exceptionCode="NoApplicableCode" locator="AccessForbidden"> <ExceptionText>Access to service is forbidden.</ExceptionText> </Exception></ExceptionReport>

# NBVAL_IGNORE_OUTPUT

import requests
from requests_magpie import MagpieAuth, MagpieAuthenticationError

BAD_USR = "an-invalid-user"
BAD_PWD = "or-bad-password"

try:
    with requests.session() as session:
        session.auth = MagpieAuth(f"https://{PAVICS_HOST}/magpie", BAD_USR, BAD_PWD)
        xr.open_dataset(
            SECURED_URL, decode_cf=False
        )  # Attributes are problematic with this file.
# specific error depends on what raises (unauthorized, forbidden, login failure) and 'xarray' version
except (OSError, HTTPError, MagpieAuthenticationError) as exc:
    print("Access with invalid credentials was not permitted as expected.")
else:
    raise RuntimeError(
        "Expected authentication failure response, but login operation did not raise!"
    )

Access with invalid credentials was not permitted as expected.

syntax error, unexpected WORD_WORD, expecting SCAN_ATTR or SCAN_DATASET or SCAN_ERROR
context: <?xml^ version="1.0" encoding="utf-8"?><ExceptionReport version="1.0.0" xmlns="http://www.opengis.net/ows/1.1" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.opengis.net/ows/1.1 http://schemas.opengis.net/ows/1.1.0/owsExceptionReport.xsd"> <Exception exceptionCode="NoApplicableCode" locator="AccessForbidden"> <ExceptionText>Access to service is forbidden.</ExceptionText> </Exception></ExceptionReport>

# NBVAL_IGNORE_OUTPUT

AUTH_USR = os.getenv("TEST_MAGPIE_AUTHTEST_USERNAME", "authtest")
AUTH_PWD = os.getenv("TEST_MAGPIE_AUTHTEST_PASSWORD", "authtest1234")

# Open session
with requests.Session() as session:
    session.auth = MagpieAuth(f"https://{PAVICS_HOST}/magpie", AUTH_USR, AUTH_PWD)
    # Open a PyDAP data store and pass it to xarray
    store = xr.backends.PydapDataStore.open(SECURED_URL, session=session)
    ds = xr.open_dataset(
        store, decode_cf=False
    )  # Attributes are problematic with this file.
ds

Working with the PAVICS THREDDS server¶

PAVICS data access¶