Support TSV as a "dialect" of CSV

csv_diff/__init__.py

@@ -4,8 +4,17 @@
 import hashlib
 
 
-def load_csv(fp, key=None):
-    fp = csv.reader(fp)
+def load_csv(fp, key=None, dialect=None):
+    if dialect is None and fp.seekable():
+        # Peek at first 1MB to sniff the delimiter and other dialect details
+        peek = fp.read(1024**2)
+        fp.seek(0)
+        try:
+            dialect = csv.Sniffer().sniff(peek, delimiters=",\t")
+        except csv.Error:
+            # Oh well, we tried. Fallback to the default.
+            pass
+    fp = csv.reader(fp, dialect=(dialect or 'excel'))
     headings = next(fp)
     rows = [dict(zip(headings, line)) for line in fp]
     if key:

csv_diff/cli.py

@@ -16,6 +16,9 @@
 @click.option(
     "--key", type=str, default=None, help="Column to use as a unique ID for each row"
 )
+@click.option(
+    "--format", type=click.Choice(["csv", "tsv"]), default=None, help="Explicitly specify input format (csv, tsv) instead of auto-detecting"
+)
 @click.option(
     "--json", type=bool, default=False, help="Output changes as JSON", is_flag=True
 )
@@ -31,9 +34,15 @@
     default=None,
     help="Plural word to use, e.g. 'trees' for '2 trees'",
 )
-def cli(previous, current, key, json, singular, plural):
+def cli(previous, current, key, format, json, singular, plural):
     "Diff two CSV files"
-    diff = compare(load_csv(open(previous), key=key), load_csv(open(current), key=key))
+    dialect = {
+        "csv": "excel",
+        "tsv": "excel-tab",
+    }
+    def load(filename):
+        return load_csv(open(filename, newline=""), key=key, dialect=dialect.get(format))
+    diff = compare(load(previous), load(current))
     if json:
         print(std_json.dumps(diff, indent=4))
     else:

tests/test_csv_diff.py

@@ -9,6 +9,10 @@
 1,Cleo,5
 2,Pancakes,2"""
 
+TWO_TSV = """id\tname\tage
+1\tCleo\t5
+2\tPancakes\t2"""
+
 THREE = """id,name,age
 1,Cleo,5"""
 
@@ -86,3 +90,16 @@ def test_columns_changed():
         "columns_added": ["weight"],
         "columns_removed": ["age"],
     } == diff
+
+
+def test_tsv():
+    diff = compare(
+        load_csv(io.StringIO(ONE), key="id"), load_csv(io.StringIO(TWO_TSV), key="id")
+    )
+    assert {
+        "added": [],
+        "removed": [],
+        "changed": [{"key": "1", "changes": {"age": ["4", "5"]}}],
+        "columns_added": [],
+        "columns_removed": [],
+    } == diff