refactor: optimize KEEP action performance by caching field contenders & fix SyntaxWarning for invalid escape sequences (#295)

* refactor: optimize KEEP action performance by caching field contenders

When multiple KEEP actions are present in a deid recipe, the
`expand_field_expression` function was internally calling
`get_fields_with_lookup(dicom)` for each KEEP action. This function
iterates through all DICOM fields and builds lookup tables, which is
an expensive operation.

This commit modifies the `keep` property to build the field contenders
once on the first KEEP action and pass it explicitly to all subsequent
`expand_field_expression` calls via the `contenders` parameter. This
avoids redundant field enumeration and lookup table construction.

This optimization significantly reduces processing time for recipes
with multiple KEEP actions, especially for DICOM files with many
fields or nested sequences.

* fix: resolve SyntaxWarning for invalid escape sequences

Convert regex patterns to raw strings (r"") in config/utils.py to
eliminate SyntaxWarning about invalid escape sequences.
This follows Python best practices for regular expressions and avoids potential issues with
escape sequences.

Author: Simlomb

CHANGELOG.md

@@ -14,6 +14,7 @@ and **Merged pull requests**. Critical items to know are:
 Referenced versions in headers are tagged on Github, in parentheses are for pypi.
 
 ## [vxx](https://github.com/pydicom/deid/tree/master) (master)
+- Optimize KEEP action performance by caching field contenders & fix SyntaxWarning for invalid escape sequences [#293](https://github.com/pydicom/deid/pull/295) (0.4.10)
 - Fix field removal and blanking to clean up child UID references [#293](https://github.com/pydicom/deid/pull/293) (0.4.9)
 - Fix UID lookup for nested sequence fields in DICOM datasets [#292](https://github.com/pydicom/deid/pull/292) (0.4.8)
 - Allow saving with a compressed transfer syntax [#290](https://github.com/pydicom/deid/pull/290) (0.4.7)

deid/config/utils.py

@@ -130,7 +130,7 @@ def load_deid(path=None):
             parts = line.split(" ")
             if len(parts) > 1:
                 section_name = " ".join(parts[1:])
-            section = re.sub("[%]|(\s+)", "", parts[0]).lower()  # noqa
+            section = re.sub(r"[%]|(\s+)", "", parts[0]).lower()  # noqa
             if section not in sections:
                 bot.exit("%s is not a valid section." % section)
 
@@ -219,7 +219,7 @@ def parse_format(line):
     ==========
     line: the line that starts with format.
     """
-    fmt = re.sub("FORMAT|(\s+)", "", line).lower()  # noqa
+    fmt = re.sub(r"FORMAT|(\s+)", "", line).lower()  # noqa
     if fmt not in formats:
         bot.exit("%s is not a valid format." % fmt)
     bot.debug("FORMAT set to %s" % fmt)

deid/dicom/parser.py

@@ -320,10 +320,18 @@ def keep(self):
         """
         keeps = []
         if self.recipe.deid is not None:
+            # Build field contenders ONCE and reuse for all KEEP actions
+            contenders = None
             for action in self.recipe.get_actions(action="KEEP"):
                 if action and action.get("field"):
+                    # Only build contenders on first iteration
+                    if contenders is None:
+                        contenders = get_fields_with_lookup(self.dicom)
+
                     fields = expand_field_expression(
-                        field=action.get("field"), dicom=self.dicom
+                        field=action.get("field"),
+                        dicom=self.dicom,
+                        contenders=contenders,  # Reuse the same contenders
                     )
                     # keys are in the format "(1234,5678)"
                     keeps.extend(fields.keys())

deid/version.py

@@ -2,7 +2,7 @@
 __copyright__ = "Copyright 2016-2025, Vanessa Sochat"
 __license__ = "MIT"
 
-__version__ = "0.4.9"
+__version__ = "0.4.10"
 AUTHOR = "Vanessa Sochat"
 AUTHOR_EMAIL = "vsoch@users.noreply.github.com"
 NAME = "deid"