Update mc4-sampling.py

mc4-sampling.py

@@ -5,7 +5,16 @@ import gzip
 import json
 
 import datasets
-import kenlm  # pip install https://github.com/kpu/kenlm/archive/master.zip
+try:
+    import kenlm  # pip install https://github.com/kpu/kenlm/archive/master.zip
+except ImportError:
+    import warnings
+    KENLM_IMPORT = (
+        "To be able to use bertin-project/mc4-sampling, you need to install the following dependency: kenlm.\n"
+        "Please install it using 'pip install https://github.com/kpu/kenlm/archive/master.zip' for instance."
+    )
+    kenlm = None
+    warnings.warn(KENLM_IMPORT)
 import numpy as np
 from numpy.random import default_rng
 
@@ -302,6 +311,8 @@ class Mc4Sampling(datasets.GeneratorBasedBuilder):
                 # http://dl.fbaipublicfiles.com/cc_net/lm/es.arpa.bin
                 logger.info("loading model = %s", str(self.perplexity_model))
                 if isinstance(self.perplexity_model, str):
+                    if not kenlm:
+                        raise ImportError(KENLM_IMPORT)
                     self.pp_model = kenlm.Model(self.perplexity_model)
                 else:
                     self.pp_model = self.perplexity_model