Add validation of SPDX license identifiers

Currently this only checks the dcterms.license field and the result
will only be a warning.

README.md

@@ -103,7 +103,6 @@ This currently uses the [Python langid](https://github.com/saffsd/langid.py) lib
 - Better logging, for example with INFO, WARN, and ERR levels
 - Verbose, debug, or quiet options
 - Warn if an author is shorter than 3 characters?
-- Validate dc.rights field against SPDX? Perhaps with an option like `-m spdx` to enable the spdx module?
 - Validate DOIs? Normalize to https://doi.org format? Or use just the DOI part: 10.1016/j.worlddev.2010.06.006
 - Warn if two items use the same file in `filename` column
 - Add an option to drop invalid AGROVOC subjects?

csv_metadata_quality/app.py

@@ -150,6 +150,11 @@ def run(argv):
         if column == "filename":
             df[column] = df[column].apply(check.filename_extension)
 
+        # Check: SPDX license identifier
+        match = re.match(r"dcterms\.license.*$", column)
+        if match is not None:
+            df[column] = df[column].apply(check.spdx_license_identifier)
+
     ##
     # Perform some checks on rows so we can consider items as a whole rather
     # than simple on a field-by-field basis. This allows us to check whether

csv_metadata_quality/check.py

@@ -3,6 +3,7 @@ from datetime import datetime, timedelta
 import pandas as pd
 import requests
 import requests_cache
+import spdx_license_list
 from colorama import Fore
 from pycountry import languages
 
@@ -317,3 +318,23 @@ def filename_extension(field):
             print(f"{Fore.YELLOW}Filename with uncommon extension: {Fore.RESET}{value}")
 
     return field
+
+
+def spdx_license_identifier(field):
+    """Check if a license is a valid SPDX identifier.
+
+    Prints the value if it is invalid.
+    """
+
+    # Skip fields with missing values
+    if pd.isna(field):
+        return
+
+    # Try to split multi-value field on "||" separator
+    for value in field.split("||"):
+        if value not in spdx_license_list.LICENSES:
+            print(f"{Fore.YELLOW}Non-SPDX license identifier: {Fore.RESET}{value}")
+
+            pass
+
+    return field

pyproject.toml

@@ -20,6 +20,7 @@ requests-cache = "^0.5.2"
 pycountry = "^19.8.18"
 langid = "^1.1.6"
 colorama = "^0.4.4"
+spdx-license-list = "^0.5.2"
 
 [tool.poetry.dev-dependencies]
 pytest = "^6.1.1"