diff --git a/gcgen/api/__init__.py b/gcgen/api/__init__.py
index 6dae04d..5edfee2 100644
--- a/gcgen/api/__init__.py
+++ b/gcgen/api/__init__.py
@@ -14,5 +14,5 @@
     "generator",
     "get_snippet",
     "write_file",
-    "Json"
+    "Json",
 ]
diff --git a/gcgen/generate.py b/gcgen/generate.py
index 8be4c01..ea23492 100644
--- a/gcgen/generate.py
+++ b/gcgen/generate.py
@@ -106,7 +106,12 @@ def scope(self, scope: Scope) -> None:
         self._scope = scope
 
     def on_snippet(
-        self, snippet_prefix: str, snippet_name: str, snippet_arg: Json, src_path: Path, fh: TextIOWrapper
+        self,
+        snippet_prefix: str,
+        snippet_name: str,
+        snippet_arg: Json,
+        src_path: Path,
+        fh: TextIOWrapper,
     ):
         logger.debug(f"on_snippet {snippet_name!r} called")
         snippet_fn: Union[SnippetFn, None] = self._snippets_scope.get(
diff --git a/gcgen/snippetparser.py b/gcgen/snippetparser.py
index 1f92186..6503d0e 100644
--- a/gcgen/snippetparser.py
+++ b/gcgen/snippetparser.py
@@ -69,7 +69,14 @@ def printerr(self) -> None:
 
 
 class SnippetJsonValueError(SnippetParseError):
-    def __init__(self, file: Path, snippet: str, value: str, json_err: JSONDecodeError, line_start: int):
+    def __init__(
+        self,
+        file: Path,
+        snippet: str,
+        value: str,
+        json_err: JSONDecodeError,
+        line_start: int,
+    ):
         self.file = file
         self.snippet = snippet
         self.line_start = line_start
@@ -81,15 +88,13 @@ def __init__(self, file: Path, snippet: str, value: str, json_err: JSONDecodeErr
             file,
             snippet,
             line_start,
-            line_start
+            line_start,
         )
 
     def printerr(self) -> None:
         print("Snippet argument parse error:")
         print("")
-        print(
-            "Error parsing argument as JSON value"
-        )
+        print("Error parsing argument as JSON value")
         print("")
         print("Details:")
         print(f"  File: {self.file}")
@@ -105,7 +110,12 @@ def __init__(self, snippet_start: str, snippet_end: str):
         self.snippet_end = snippet_end
 
     def on_snippet(
-        self, snippet_prefix: str, snippet_name: str, snippet_arg: Json, src_path: Path, fh: TextIOWrapper
+        self,
+        snippet_prefix: str,
+        snippet_name: str,
+        snippet_arg: Json,
+        src_path: Path,
+        fh: TextIOWrapper,
     ):
         pass
 
@@ -133,7 +143,9 @@ def parse(self, fpath: Path, dpath: Path):
                         if ndx != -1:
                             cont = True
                             prefix = line[0:ndx]
-                            parts = line[ndx + len(snippet_start):].strip().split(" ", 1)
+                            parts = (
+                                line[ndx + len(snippet_start) :].strip().split(" ", 1)
+                            )
                             if len(parts) == 1:
                                 snippet_name = parts[0]
                                 snippet_arg = None
@@ -148,7 +160,11 @@ def parse(self, fpath: Path, dpath: Path):
                                         snippet_arg = json.loads(snippet_arg)
                                     except JSONDecodeError as e:
                                         raise SnippetJsonValueError(
-                                            fpath, snippet_name, snippet_arg_raw, e, lineno
+                                            fpath,
+                                            snippet_name,
+                                            snippet_arg_raw,
+                                            e,
+                                            lineno,
                                         ) from e
                             break
 
@@ -174,7 +190,9 @@ def parse(self, fpath: Path, dpath: Path):
                     for line in src:
                         lineno += 1
                         if line.startswith(s_end):
-                            self.on_snippet(snippet_prefix, snippet_name, snippet_arg, fpath, dst)
+                            self.on_snippet(
+                                snippet_prefix, snippet_name, snippet_arg, fpath, dst
+                            )
                             dst.write(line)  # retain the snippet end line
                             cont = True
                             break
diff --git a/tests/test_gentests.py b/tests/test_gentests.py
index 1243502..979da5f 100644
--- a/tests/test_gentests.py
+++ b/tests/test_gentests.py
@@ -6,7 +6,11 @@
 from setuptools._distutils.dir_util import copy_tree
 from typing import Dict, List
 from gcgen import generate
-from gcgen.snippetparser import UnclosedSnippetError, NestedSnippetsError, SnippetJsonValueError
+from gcgen.snippetparser import (
+    UnclosedSnippetError,
+    NestedSnippetsError,
+    SnippetJsonValueError,
+)
 import pytest
 import logging
 
@@ -155,9 +159,7 @@ def test_bb_snippets_calling_snippets():
 
 
 def test_bb_snippets_json_args():
-    gentest_test_eql(
-        "bb-snippets-json-args", ["example.txt"]
-    )
+    gentest_test_eql("bb-snippets-json-args", ["example.txt"])
 
 
 def test_bb_snippets_json_args_err():
diff --git a/tests/test_parser.py b/tests/test_parser.py
index 84fe003..59a0716 100644
--- a/tests/test_parser.py
+++ b/tests/test_parser.py
@@ -42,13 +42,16 @@ def parse(self, fpath: Path, dpath: Path):
         super().parse(fpath, dpath)
 
     def on_snippet(
-        self, snippet_prefix: str, snippet_name: str, snippet_arg: snippetparser.Json, src_path: Path, fh: TextIOWrapper
+        self,
+        snippet_prefix: str,
+        snippet_name: str,
+        snippet_arg: snippetparser.Json,
+        src_path: Path,
+        fh: TextIOWrapper,
     ):
-        self._results.append(SnippetResult(
-            name=snippet_name,
-            prefix=snippet_prefix,
-            args=snippet_arg
-        ))
+        self._results.append(
+            SnippetResult(name=snippet_name, prefix=snippet_prefix, args=snippet_arg)
+        )
         # pass
 
 
@@ -70,7 +73,7 @@ def test_prog_w_noarg_snippets():
         parser.parse(fpath, fpath)
         assert parser._results == [
             SnippetResult(name="hello", prefix="", args=None),
-            SnippetResult(name="smth", prefix="    ", args=None)
+            SnippetResult(name="smth", prefix="    ", args=None),
         ]
 
 
@@ -105,5 +108,9 @@ def test_prog_w_json_args():
             SnippetResult(name="hello", prefix="", args=None),
             SnippetResult(name="hello", prefix="", args="Jacque"),
             SnippetResult(name="print_files", prefix="    ", args=["file1", "file2"]),
-            SnippetResult(name="mk_user", prefix="    ", args={"username": "jane", "groups": ["wheel", "docker"]}),
+            SnippetResult(
+                name="mk_user",
+                prefix="    ",
+                args={"username": "jane", "groups": ["wheel", "docker"]},
+            ),
         ]