MAINT: avoid modifying mutable default values

2 files changed, 9 insertions, 4 deletions

diff --git a/numpy/distutils/command/config_compiler.py b/numpy/distutils/command/config_compiler.py
index 5e638fecc..bf170063e 100644
--- a/numpy/distutils/command/config_compiler.py
+++ b/numpy/distutils/command/config_compiler.py
@@ -5,9 +5,12 @@ from numpy.distutils import log
 
 #XXX: Linker flags
 
-def show_fortran_compilers(_cache=[]):
-    # Using cache to prevent infinite recursion
-    if _cache: return
+def show_fortran_compilers(_cache=None):
+    # Using cache to prevent infinite recursion.
+    if _cache:
+        return
+    elif _cache is None:
+        _cache = []
     _cache.append(1)
     from numpy.distutils.fcompiler import show_fcompilers
     import distutils.core
diff --git a/numpy/distutils/core.py b/numpy/distutils/core.py
index d9e125368..70cc37caa 100644
--- a/numpy/distutils/core.py
+++ b/numpy/distutils/core.py
@@ -71,12 +71,14 @@ def _dict_append(d, **kws):
         else:
             raise TypeError(repr(type(dv)))
 
-def _command_line_ok(_cache=[]):
+def _command_line_ok(_cache=None):
     """ Return True if command line does not contain any
     help or display requests.
     """
     if _cache:
         return _cache[0]
+    elif _cache is None:
+        _cache = []
     ok = True
     display_opts = ['--'+n for n in Distribution.display_option_names]
     for o in Distribution.display_options: