moved zero division solve to _set_N_, and tests

benford/stats.py

@@ -14,8 +14,6 @@ def Z_score(frame, N):
         Series of computed Z scores, or zero if N==0, so there is no
             DivisionByZero
     """
-    if N == 0:
-        return 0
     return (frame.AbsDif - (1 / (2 * N))) / sqrt(
            (frame.Expected * (1. - frame.Expected)) / N)
 

benford/utils.py

@@ -10,13 +10,13 @@ def _set_N_(len_df, limit_N):
     """"""
     # Assigning to N the superior limit or the lenght of the series
     if limit_N is None or limit_N > len_df:
-        return len_df
+        return max(1, len_df)
     # Check on limit_N being a positive integer
     else:
         if limit_N < 0 or not isinstance(limit_N, int):
             raise ValueError("limit_N must be None or a positive integer.")
         else:
-            return limit_N
+            return max(1, limit_N)
 
 
 def get_mantissas(arr):

tests/conftest.py

@@ -9,6 +9,10 @@ def gen_N():
     return np.random.randint(0, 25000)
 
 
+@pytest.fixture
+def gen_N_lower(gen_N):
+    return np.random.randint(0, gen_N)
+
 @pytest.fixture
 def gen_array(gen_N):
     num = gen_N

tests/test_utils.py

@@ -5,13 +5,12 @@
 
 
 
-def test_set_N_Limit_None():
-    assert ut._set_N_(100, None) == 100
+def test_set_N_Limit_None(gen_N):
+    assert ut._set_N_(gen_N, None) == gen_N
 
 
-def test_set_N_Limit_greater():
-    assert ut._set_N_(100, 99) == 99
-    assert ut._set_N_(1000, 750) == 750
+def test_set_N_Limit_greater(gen_N, gen_N_lower):
+    assert ut._set_N_(gen_N, gen_N_lower) == gen_N_lower
 
 
 def test_set_N_negative():
@@ -23,12 +22,14 @@ def test_set_N_float():
     with pytest.raises(ValueError) as context:
         ut._set_N_(127.8, -100)
 
+def test_set_N_zero(gen_N):
+    assert ut._set_N_(0, None) == 1
+    assert ut._set_N_(0, gen_N) == 1
 
 def test_get_mantissas_less_than_1(gen_array):
     assert sum(ut.get_mantissas(gen_array) > 1) == 0
 
 
-
 def test_get_mantissas_less_than_0(gen_array):
     assert sum(ut.get_mantissas(gen_array) < 0) == 0