Escape regex special characters in FITS keyword values used for IFC filtering

CHANGES.rst

@@ -10,6 +10,10 @@ Other Changes and Additions
 Bug Fixes
 ^^^^^^^^^
 
+- When filtering an ``ImageFileCollection`` by keyword value, and not
+  explicitly using a regex search pattern (``regex_match=True``), escape all
+  special characters in the keyword value for a successful search. [#770]
+
 2.1.1 (2021-03-15)
 ------------------
 

ccdproc/image_collection.py

@@ -710,6 +710,8 @@ def _find_keywords_by_values(self, **kwd):
                         pattern = re.compile(value,
                                              flags=re.IGNORECASE)
                     else:
+                        # Escape all special characters that might be present
+                        value = re.escape(value)
                         # This pattern matches the prior behavior.
                         pattern = re.compile('^' + value + '$',
                                              flags=re.IGNORECASE)

ccdproc/tests/test_image_collection.py

@@ -1100,3 +1100,28 @@ def test_filtered_collection_with_no_files(self, triage_setup):
         ifc = ImageFileCollection(triage_setup.test_dir)
 
         ifc_no_files = ifc.filter(object='really fake object')
+
+    def test_filter_on_regex_escape_characters(self, triage_setup):
+        # Test for implementation of bugfix at
+        #
+        #    https://github.com/astropy/ccdproc/issues/770
+        #
+        # which escapes regex special characters in keyword values used for
+        # filtering a collection, when option `regex_match=False`.
+
+        # For a few different special characters, make test files with FILTER
+        # keyword containing these
+
+        special_kwds = ['CO+', 'GG420 (1)', 'V|R|I', 'O[III]', 'NaD^2']
+        for i,kw in enumerate(special_kwds,1):
+            hdu = fits.PrimaryHDU()
+            hdu.data = np.zeros((5, 5))
+            hdu.header['REGEX_FL'] = kw
+            hdu.writeto(os.path.join(triage_setup.test_dir,
+                        'regex_special_{:d}.fits'.format(i)))
+
+        ic = ImageFileCollection(triage_setup.test_dir)
+        for kw in special_kwds:
+            new_ic = ic.filter(regex_fl=kw)
+            assert len(new_ic.files) == 1
+            assert kw in new_ic.summary['regex_fl']