Add support for expr.setParseAction(None) to clear all parse actions

3 files changed, 29 insertions, 3 deletions

diff --git a/CHANGES b/CHANGES
index af8a04f..c731b33 100644
--- a/CHANGES
+++ b/CHANGES
@@ -9,6 +9,10 @@ Version 2.4.1 -
   example, which makes the bug-fixing process a lot easier,
   thanks!
 
+- Modified setParseAction to accept None as an argument,
+  indicating that all previously-defined parse actions for the
+  expression should be cleared.
+
 - Modified runTests to call postParse function before dumping out
   the parsed results - allows for postParse to add further results,
   such as indications of additional validation success/failure.
diff --git a/pyparsing.py b/pyparsing.py
index 4cb96df..b94040a 100644
--- a/pyparsing.py
+++ b/pyparsing.py
@@ -96,7 +96,7 @@ classes inherit from. Use the docstrings for examples of how to:
 """
 
 __version__ = "2.4.1"
-__versionTime__ = "29 Jun 2019 05:25 UTC"
+__versionTime__ = "29 Jun 2019 06:17 UTC"
 __author__ = "Paul McGuire <ptmcg@users.sourceforge.net>"
 
 import string
@@ -1418,6 +1418,9 @@ class ParserElement(object):
         value from fn, and the modified list of tokens will replace the original.
         Otherwise, fn does not need to return any value.
 
+        If None is passed as the parse action, all previously added parse actions for this
+        expression are cleared.
+
         Optional keyword arguments:
         - callDuringTry = (default= ``False`` ) indicate if parse action should be run during lookaheads and alternate testing
 
@@ -1441,8 +1444,13 @@ class ParserElement(object):
             # note that integer fields are now ints, not strings
             date_str.parseString("1999/12/31")  # -> [1999, '/', 12, '/', 31]
         """
-        self.parseAction = list(map(_trim_arity, list(fns)))
-        self.callDuringTry = kwargs.get("callDuringTry", False)
+        if list(fns) == [None, ]:
+            self.parseAction = None
+        else:
+            if not all(callable(fn) for fn in fns):
+                raise TypeError("parse actions must be callable")
+            self.parseAction = list(map(_trim_arity, list(fns)))
+            self.callDuringTry = kwargs.get("callDuringTry", False)
         return self
 
     def addParseAction( self, *fns, **kwargs ):
diff --git a/unitTests.py b/unitTests.py
index e14016a..4c6c9ab 100644
--- a/unitTests.py
+++ b/unitTests.py
@@ -3009,6 +3009,20 @@ class TrimArityExceptionMaskingTest2(ParseTestCase):
 
         K()
 
+
+class ClearParseActionsTest(ParseTestCase):
+    def runTest(self):
+        import pyparsing as pp
+        ppc = pp.pyparsing_common
+
+        realnum = ppc.real()
+        self.assertEqual(realnum.parseString("3.14159")[0], 3.14159, "failed basic real number parsing")
+
+        # clear parse action that converts to float
+        realnum.setParseAction(None)
+        self.assertEqual(realnum.parseString("3.14159")[0], "3.14159", "failed clearing parse action")
+
+
 class OneOrMoreStopTest(ParseTestCase):
     def runTest(self):
         from pyparsing import (Word, OneOrMore, alphas, Keyword, CaselessKeyword,