py: Don't try to optimise for+range when args are not simple expressions.

Addresses issue #1693.

tests/basics/for_range.py

@@ -0,0 +1,58 @@
+# test for+range, mostly to check optimisation of this pair
+
+# apply args using *
+for x in range(*(1, 3)):
+    print(x)
+for x in range(1, *(6, 2)):
+    print(x)
+
+# apply args using **
+try:
+    for x in range(**{'end':1}):
+        print(x)
+except TypeError:
+    print('TypeError')
+try:
+    for x in range(0, **{'end':1}):
+        print(x)
+except TypeError:
+    print('TypeError')
+try:
+    for x in range(0, 1, **{'step':1}):
+        print(x)
+except TypeError:
+    print('TypeError')
+
+# keyword args
+try:
+    for x in range(end=1):
+        print(x)
+except TypeError:
+    print('TypeError')
+try:
+    for x in range(0, end=1):
+        print(x)
+except TypeError:
+    print('TypeError')
+try:
+    for x in range(0, 1, step=1):
+        print(x)
+except TypeError:
+    print('TypeError')
+
+# argument is a comprehension
+try:
+    for x in range(0 for i in []):
+        print(x)
+except TypeError:
+    print('TypeError')
+try:
+    for x in range(0, (0 for i in [])):
+        print(x)
+except TypeError:
+    print('TypeError')
+try:
+    for x in range(0, 1, (0 for i in [])):
+        print(x)
+except TypeError:
+    print('TypeError')