MRG: avoid compressing sig files in directory output twice (#2752)

Fixes #2751

src/sourmash/save_load.py

@@ -348,7 +348,7 @@ def add(self, ss):
                     break
                 i += 1
 
-        with gzip.open(outname, "wb") as fp:
+        with open(outname, "wb") as fp:
             sigmod.save_signatures([ss], fp, compression=1)
 
 

tests/test_sourmash_args.py

@@ -11,6 +11,7 @@
 import csv
 import argparse
 import shutil
+import json
 
 import sourmash_tst_utils as utils
 import sourmash
@@ -363,6 +364,29 @@ def test_save_signatures_to_location_1_dirout(runtmp):
     assert len(saved) == 2
 
 
+def test_save_signatures_to_location_1_dirout_bug_2751(runtmp):
+    # check for 2x compressed sig files
+    sig2 = utils.get_test_data('2.fa.sig')
+    ss2 = sourmash.load_one_signature(sig2, ksize=31)
+    sig47 = utils.get_test_data('47.fa.sig')
+    ss47 = sourmash.load_one_signature(sig47, ksize=31)
+
+    outloc = runtmp.output('sigout/')
+    with sourmash_args.SaveSignaturesToLocation(outloc) as save_sig:
+        print(save_sig)
+        save_sig.add(ss2)
+        save_sig.add(ss47)
+
+    assert os.path.isdir(outloc)
+    print(os.listdir(outloc))
+
+    outloc2 = runtmp.output('sigout/09a08691ce52952152f0e866a59f6261.sig.gz')
+    with gzip.open(outloc2, "r") as fp:
+        data = fp.read()
+        print(data)
+        _ = json.loads(data)
+
+
 def test_save_signatures_to_location_1_dirout_duplicate(runtmp):
     # save to sigout/ (directory)
     sig2 = utils.get_test_data('2.fa.sig')