--- a/rql/stmts.py	Wed Feb 13 18:36:40 2019 +0100
+++ b/rql/stmts.py	Wed Feb 13 18:41:43 2019 +0100
@@ -272,7 +272,8 @@
           returning a string
         """
         if tr is None:
-            tr = lambda x, **k: x
+            def tr(x, **k):
+                return x
         return [c.get_description(mainindex, tr) for c in self.children]
 
     # repr / as_string / copy #################################################
@@ -490,7 +491,8 @@
         if userepr:
             as_string = repr
         else:
-            as_string = lambda x: x.as_string(kwargs=kwargs)
+            def as_string(x):
+                return x.as_string(kwargs=kwargs)
         s = [','.join(as_string(term) for term in self.selection)]
         if self.groupby:
             s.append('GROUPBY ' + ','.join(as_string(term)

--- a/tox.ini	Wed Feb 13 18:36:40 2019 +0100
+++ b/tox.ini	Wed Feb 13 18:41:43 2019 +0100
@@ -11,7 +11,7 @@
 basepython = python3
 deps =
   flake8
-commands = flake8 {posargs:--ignore=E501,E731,E741,F401,F401,F403,F405,F811,F821,F841,E123,E226,W503,E241,W504,E126,E121}
+commands = flake8 {posargs:--ignore=E501,E741,F401,F401,F403,F405,F811,F821,F841,E123,E226,W503,E241,W504,E126,E121}
 
 [pytest]
 python_files = *test_*.py