Please the linter

- Do not use lambda
 - Replace assert with raise
 - Minor fixes

techrec/forge.py

@@ -70,13 +70,16 @@ def mp3_join(named_intervals):
     for (filename, start_cut, end_cut) in named_intervals:
         # this happens only one time, and only at the first iteration
         if start_cut:
-            assert startskip is None
+            if startskip is not None:
+                raise Exception("error in first cut iteration")
             startskip = start_cut
-        # this happens only one time, and only at the first iteration
+        # this happens only one time, and only at the last iteration
         if end_cut:
-            assert endskip is None
+            if endskip is not None:
+                raise Exception("error in last iteration")
             endskip = end_cut
-        assert "|" not in filename
+        if "|" in filename:
+            raise Exception(f"'|' in {filename}")
         files.append(filename)
 
     cmdline = [ffmpeg, "-i", "concat:%s" % "|".join(files)]
@@ -96,10 +99,13 @@ def create_mp3(
     outfile: str,
     options={},
     validator: Optional[Validator] = None,
-    **kwargs
+    **kwargs,
 ):
     if validator is None:
-        validator = lambda s, e, f: True
+
+        def validator(s, e, f):
+            return True
+
     intervals = [
         (get_timefile(begin), start_cut, end_cut)
         for begin, start_cut, end_cut in get_files_and_intervals(start, end)
@@ -162,7 +168,7 @@ def create_mp3(
         os.kill(p.pid, 15)
         try:
             os.remove(tmp_file.name)
-        except:
+        except Exception:
             pass
         raise Exception("timeout")  # TODO: make a specific TimeoutError
     if p.returncode != 0: