Avoid generating pydicom user warnings

bidscoin/bids.py

@@ -1770,10 +1770,10 @@ def get_dicomfield(tagname: str, dicomfile: Path) -> Union[str, int]:
                 else:
                     dicomdata = _DICOMDICT_CACHE
 
-                try:                                                    # Try Pydicom's hexadecimal tag number first
-                    value = eval(f"dicomdata[{tagname}].value")         # NB: This may generate e.g. UserWarning: Invalid value 'filepath' used with the 'in' operator: must be an element tag as a 2-tuple or int, or an element keyword
-                except (NameError, KeyError, SyntaxError):
-                    value = dicomdata.get(tagname,'') if tagname in dicomdata else ''  # Then try and see if it is an attribute name. NB: Do not use dicomdata.get(tagname, '') to avoid using its class attributes (e.g. 'filename')
+                if re.fullmatch(r'\(?0x[\dA-Z]*,?(0x)?[\dA-Z]*\)?', tagname):              # Try Pydicom's hexadecimal tag number first (must be a 2-tuple or int)
+                    value = eval(f"dicomdata[{tagname}].value")                                 # NB: This may generate e.g. UserWarning: Invalid value 'filepath' used with the 'in' operator: must be an element tag as a 2-tuple or int, or an element keyword
+                else:
+                    value = dicomdata.get(tagname,'') if tagname in dicomdata else ''       # Then try and see if it is an attribute name. NB: Do not use dicomdata.get(tagname, '') to avoid using its class attributes (e.g. 'filename')
 
                 # Try a recursive search
                 if not value and value != 0: