diff --git a/setup.cfg b/setup.cfg
index 8d1258d..d638129 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -19,7 +19,8 @@ warn_redundant_casts = True
 
 
 [tool:isort]
-known_third_party = click,pathlib2
+known_first_party = pycalver,pycalver2
+known_third_party = click,pathlib2,lexid
 force_single_line = True
 length_sort = True
 
@@ -161,3 +162,8 @@ disable =
     missing-class-docstring,
     missing-function-docstring,
     raise-missing-from,
+    duplicate-code,
+
+generated-members =
+    # members of typing.NamedTuple
+    "(_replace|_asdict|_fields)",
diff --git a/src/pycalver/__main__.py b/src/pycalver/__main__.py
index 7149fc2..2f10642 100755
--- a/src/pycalver/__main__.py
+++ b/src/pycalver/__main__.py
@@ -15,10 +15,10 @@ import logging
 import subprocess as sp
 
 import click
-import pycalver2.version as v2version
 
 import pycalver.cli as v1cli
 import pycalver.version as v1version
+import pycalver2.version as v2version
 from pycalver import vcs
 from pycalver import config
 
diff --git a/src/pycalver/rewrite.py b/src/pycalver/rewrite.py
index ddc5146..fffdc52 100644
--- a/src/pycalver/rewrite.py
+++ b/src/pycalver/rewrite.py
@@ -13,12 +13,11 @@ import logging
 
 import pathlib2 as pl
 
+import pycalver.version as v1version
+import pycalver.patterns as v1patterns
 from pycalver import parse
 from pycalver import config
 
-from . import version
-from . import patterns
-
 logger = logging.getLogger("pycalver.rewrite")
 
 
@@ -78,12 +77,12 @@ def iter_file_paths(
 
 def rewrite_lines(
     pattern_strs: typ.List[str],
-    new_vinfo   : version.VersionInfo,
+    new_vinfo   : v1version.VersionInfo,
     old_lines   : typ.List[str],
 ) -> typ.List[str]:
     """Replace occurances of pattern_strs in old_lines with new_vinfo.
 
-    >>> new_vinfo = version.parse_version_info("v201811.0123-beta")
+    >>> new_vinfo = v1version.parse_version_info("v201811.0123-beta")
     >>> pattern_strs = ['__version__ = "{pycalver}"']
     >>> rewrite_lines(pattern_strs, new_vinfo, ['__version__ = "v201809.0002-beta"'])
     ['__version__ = "v201811.0123-beta"']
@@ -97,7 +96,7 @@ def rewrite_lines(
 
     for match in parse.iter_matches(old_lines, pattern_strs):
         found_patterns.add(match.pattern)
-        replacement = version.format_version(new_vinfo, match.pattern)
+        replacement = v1version.format_version(new_vinfo, match.pattern)
         span_l, span_r = match.span
         new_line = match.line[:span_l] + replacement + match.line[span_r:]
         new_lines[match.lineno] = new_line
@@ -106,7 +105,7 @@ def rewrite_lines(
     if non_matched_patterns:
         for non_matched_pattern in non_matched_patterns:
             logger.error(f"No match for pattern '{non_matched_pattern}'")
-            compiled_pattern_str = patterns.compile_pattern_str(non_matched_pattern)
+            compiled_pattern_str = v1patterns.compile_pattern_str(non_matched_pattern)
             logger.error(f"Pattern compiles to regex '{compiled_pattern_str}'")
         raise NoPatternMatch("Invalid pattern(s)")
     else:
@@ -115,19 +114,19 @@ def rewrite_lines(
 
 def rfd_from_content(
     pattern_strs: typ.List[str],
-    new_vinfo   : version.VersionInfo,
+    new_vinfo   : v1version.VersionInfo,
     content     : str,
 ) -> RewrittenFileData:
     r"""Rewrite pattern occurrences with version string.
 
-    >>> new_vinfo = version.parse_version_info("v201809.0123")
+    >>> new_vinfo = v1version.parse_version_info("v201809.0123")
     >>> pattern_strs = ['__version__ = "{pycalver}"']
     >>> content = '__version__ = "v201809.0001-alpha"'
     >>> rfd = rfd_from_content(pattern_strs, new_vinfo, content)
     >>> rfd.new_lines
     ['__version__ = "v201809.0123"']
     >>>
-    >>> new_vinfo = version.parse_version_info("v1.2.3", "v{semver}")
+    >>> new_vinfo = v1version.parse_version_info("v1.2.3", "v{semver}")
     >>> pattern_strs = ['__version__ = "v{semver}"']
     >>> content = '__version__ = "v1.2.2"'
     >>> rfd = rfd_from_content(pattern_strs, new_vinfo, content)
@@ -142,12 +141,12 @@ def rfd_from_content(
 
 def iter_rewritten(
     file_patterns: config.PatternsByGlob,
-    new_vinfo    : version.VersionInfo,
+    new_vinfo    : v1version.VersionInfo,
 ) -> typ.Iterable[RewrittenFileData]:
     r'''Iterate over files with version string replaced.
 
     >>> file_patterns = {"src/pycalver/__init__.py": ['__version__ = "{pycalver}"']}
-    >>> new_vinfo = version.parse_version_info("v201809.0123")
+    >>> new_vinfo = v1version.parse_version_info("v201809.0123")
     >>> rewritten_datas = iter_rewritten(file_patterns, new_vinfo)
     >>> rfd = list(rewritten_datas)[0]
     >>> expected = [
@@ -192,10 +191,10 @@ def diff_lines(rfd: RewrittenFileData) -> typ.List[str]:
     return list(lines)
 
 
-def diff(new_vinfo: version.VersionInfo, file_patterns: config.PatternsByGlob) -> str:
+def diff(new_vinfo: v1version.VersionInfo, file_patterns: config.PatternsByGlob) -> str:
     r"""Generate diffs of rewritten files.
 
-    >>> new_vinfo = version.parse_version_info("v201809.0123")
+    >>> new_vinfo = v1version.parse_version_info("v201809.0123")
     >>> file_patterns = {"src/pycalver/__init__.py": ['__version__ = "{pycalver}"']}
     >>> diff_str = diff(new_vinfo, file_patterns)
     >>> lines = diff_str.split("\n")
@@ -233,7 +232,7 @@ def diff(new_vinfo: version.VersionInfo, file_patterns: config.PatternsByGlob) -
     return full_diff
 
 
-def rewrite(file_patterns: config.PatternsByGlob, new_vinfo: version.VersionInfo) -> None:
+def rewrite(file_patterns: config.PatternsByGlob, new_vinfo: v1version.VersionInfo) -> None:
     """Rewrite project files, updating each with the new version."""
     fobj: typ.IO[str]
 
diff --git a/src/pycalver/version.py b/src/pycalver/version.py
index 25afe53..e6597e0 100644
--- a/src/pycalver/version.py
+++ b/src/pycalver/version.py
@@ -12,7 +12,7 @@ import datetime as dt
 import lexid
 import pkg_resources
 
-from . import patterns
+import pycalver.patterns as v1patterns
 
 logger = logging.getLogger("pycalver.version")
 
@@ -263,7 +263,7 @@ class PatternError(Exception):
 def _parse_pattern_groups(pattern_groups: PatternGroups) -> FieldValues:
     for part_name in pattern_groups.keys():
         is_valid_part_name = (
-            part_name in patterns.COMPOSITE_PART_PATTERNS or part_name in PATTERN_PART_FIELDS
+            part_name in v1patterns.COMPOSITE_PART_PATTERNS or part_name in PATTERN_PART_FIELDS
         )
         if not is_valid_part_name:
             err_msg = f"Invalid part '{part_name}'"
@@ -318,7 +318,7 @@ def parse_version_info(version_str: str, pattern: str = "{pycalver}") -> Version
     >>> vnfo = parse_version_info("1.23.456", pattern="{semver}")
     >>> assert vnfo == _parse_version_info({'MAJOR': "1", 'MINOR': "23", 'PATCH': "456"})
     """
-    regex = patterns.compile_pattern(pattern)
+    regex = v1patterns.compile_pattern(pattern)
     match = regex.match(version_str)
     if match is None:
         err_msg = (
@@ -414,7 +414,7 @@ def format_version(vinfo: VersionInfo, pattern: str) -> str:
     'v1.02.034'
     """
     full_pattern = pattern
-    for part_name, full_part_format in patterns.FULL_PART_FORMATS.items():
+    for part_name, full_part_format in v1patterns.FULL_PART_FORMATS.items():
         full_pattern = full_pattern.replace("{" + part_name + "}", full_part_format)
 
     kwargs: typ.Dict[str, typ.Union[str, int, None]] = vinfo._asdict()
diff --git a/src/pycalver2/cli.py b/src/pycalver2/cli.py
index 23d4913..107d4b8 100644
--- a/src/pycalver2/cli.py
+++ b/src/pycalver2/cli.py
@@ -14,7 +14,6 @@ import logging
 
 import pycalver2.rewrite as v2rewrite
 import pycalver2.version as v2version
-
 from pycalver import config
 
 logger = logging.getLogger("pycalver2.cli")
diff --git a/src/pycalver2/patterns.py b/src/pycalver2/patterns.py
index 07bae57..82cc585 100644
--- a/src/pycalver2/patterns.py
+++ b/src/pycalver2/patterns.py
@@ -176,6 +176,8 @@ FULL_PART_FORMATS = {
 
 
 def _replace_pattern_parts(pattern: str) -> str:
+    # The pattern is escaped, so that everything besides the format
+    # string variables is treated literally.
     for part_name, part_pattern in PART_PATTERNS.items():
         named_part_pattern = f"(?P<{part_name}>{part_pattern})"
         placeholder        = "\u005c{" + part_name + "\u005c}"
diff --git a/src/pycalver2/rewrite.py b/src/pycalver2/rewrite.py
index c5592d7..e2baeb2 100644
--- a/src/pycalver2/rewrite.py
+++ b/src/pycalver2/rewrite.py
@@ -9,12 +9,11 @@ import io
 import typing as typ
 import logging
 
-from pycalver2 import version
-from pycalver2 import patterns
-
 from pycalver import parse
 from pycalver import config
 from pycalver import rewrite as v1rewrite
+from pycalver2 import version
+from pycalver2 import patterns
 
 logger = logging.getLogger("pycalver2.rewrite")
 
diff --git a/src/pycalver2/version.py b/src/pycalver2/version.py
index 4abaacf..ea78d3f 100644
--- a/src/pycalver2/version.py
+++ b/src/pycalver2/version.py
@@ -12,7 +12,8 @@ import datetime as dt
 import lexid
 import pkg_resources
 
-from . import patterns
+# import pycalver.patterns as v1patterns
+import pycalver2.patterns as v2patterns
 
 logger = logging.getLogger("pycalver.version")
 
@@ -300,7 +301,7 @@ class PatternError(Exception):
 def _parse_pattern_groups(pattern_groups: PatternGroups) -> FieldValues:
     for part_name in pattern_groups.keys():
         is_valid_part_name = (
-            part_name in patterns.COMPOSITE_PART_PATTERNS or part_name in PATTERN_PART_FIELDS
+            part_name in v2patterns.COMPOSITE_PART_PATTERNS or part_name in PATTERN_PART_FIELDS
         )
         if not is_valid_part_name:
             err_msg = f"Invalid part '{part_name}'"
@@ -361,7 +362,7 @@ def parse_version_info(version_str: str, pattern: str = "{pycalver}") -> Version
     >>> vnfo = parse_version_info("1.23.456", pattern="{semver}")
     >>> assert vnfo == _parse_version_info({'MAJOR': "1", 'MINOR': "23", 'PATCH': "456"})
     """
-    regex = patterns.compile_pattern(pattern)
+    regex = v2patterns.compile_pattern(pattern)
     match = regex.match(version_str)
     if match is None:
         err_msg = (
@@ -447,7 +448,7 @@ def _compile_format_template(pattern: str, kwargs: TemplateKwargs) -> str:
     # NOTE (mb 2020-09-04): Some parts are optional, we need the kwargs to
     #   determine if part is set to its zero value
     format_tmpl = pattern
-    for part_name, full_part_format in patterns.FULL_PART_FORMATS.items():
+    for part_name, full_part_format in v2patterns.FULL_PART_FORMATS.items():
         format_tmpl = format_tmpl.replace("{" + part_name + "}", full_part_format)
     return format_tmpl
 
diff --git a/test/test_cli.py b/test/test_cli.py
index fcac244..38355a2 100644
--- a/test/test_cli.py
+++ b/test/test_cli.py
@@ -8,10 +8,10 @@ import subprocess as sp
 
 import pytest
 import pathlib2 as pl
-import pycalver2.patterns as patterns
 from click.testing import CliRunner
 
 import pycalver.config as config
+import pycalver2.patterns as patterns
 from pycalver.__main__ import cli
 
 SETUP_CFG_FIXTURE = """
diff --git a/test/test_patterns.py b/test/test_patterns.py
index 89c44b2..61d8d48 100644
--- a/test/test_patterns.py
+++ b/test/test_patterns.py
@@ -1,9 +1,9 @@
 import re
 
 import pytest
-import pycalver2.patterns as v2patterns
 
 import pycalver.patterns as v1patterns
+import pycalver2.patterns as v2patterns
 
 # TODO (mb 2020-09-06): test for v2patterns
 
diff --git a/test/test_rewrite.py b/test/test_rewrite.py
index 7d2693c..1eb0dd7 100644
--- a/test/test_rewrite.py
+++ b/test/test_rewrite.py
@@ -3,12 +3,11 @@
 import copy
 from test import util
 
-from pycalver2 import rewrite as v2rewrite
-from pycalver2 import version as v2version
-
 from pycalver import config
 from pycalver import rewrite as v1rewrite
 from pycalver import version as v1version
+from pycalver2 import rewrite as v2rewrite
+from pycalver2 import version as v2version
 
 REWRITE_FIXTURE = """
 # SPDX-License-Identifier: MIT