newreference: If gene is given but not found in genbank, error out

Currently, if the --gene option is used and the gene name is not found,
the script will use the entire genome which may cause some silent undesired
behaviors.

This commit changes that such that the script will error out if the gene
is not found in the GenBank file as this indicates the gene name may be
misspelled or the user may be using the wrong GenBank file.

If the --gene option is not used, the script will continue to process the
entire genome as expected.

Co-authored-by: Jover Lee <joverlee521@gmail.com>

Author: j23414

scripts/newreference.py

@@ -3,6 +3,7 @@
 from Bio.SeqFeature import SeqFeature, FeatureLocation, Seq
 import shutil
 import argparse
+import sys
 
 def new_reference(referencefile, outgenbank, outfasta, gene):
     ref = SeqIO.read(referencefile, "genbank")
@@ -17,6 +18,12 @@ def new_reference(referencefile, outgenbank, outfasta, gene):
                 startofgene = int(list(feature.location)[0])
                 endofgene =  int(list(feature.location)[-1])+1
 
+    # If user provides a --gene 'some name' is not found, print a warning and use the entire genome.
+    # Otherwise do not print a warning.
+    if(gene is not None and startofgene is None and endofgene is None):
+        print(f"ERROR: No '{gene}' was found under 'gene' or 'CDS' features in the GenBank file.", file=sys.stderr)
+        sys.exit(1)
+
     record = ref[startofgene:endofgene]
     source_feature =  SeqFeature(FeatureLocation(start=0, end=len(record)), type='source',
                                  qualifiers=ref_source_feature.qualifiers)