feat: use math.prod instead of a for loop

.grit/patterns/importing.md

@@ -100,12 +100,14 @@ pattern ensure_import_from($source) {
 
 pattern ensure_imported() {
     $name where {
-      and {
-        $program <: not contains python_import(source=$source) where {
-          $source = $name,
-        },
-        $GLOBAL_BARE_IMPORTS += [$name]
-      }
+        and {
+            $program <: not contains python_import(source=$name),
+            if ($GLOBAL_BARE_IMPORTS <: not some $name) {
+                $GLOBAL_BARE_IMPORTS += [$name]
+            } else {
+                true
+            }
+        }
     }
 }
 

.grit/patterns/math_prod.md

@@ -0,0 +1,100 @@
+---
+title: Use `math.prod` instead of multiplying in a loop
+---
+
+This pattern transforms a loop that computes the product of a list of numbers into a call to `math.prod` (introduced in Python 3.8).
+
+
+```grit
+engine marzano(0.1)
+language python
+
+pattern prod_init($accum) {
+    or {
+        `$accum = 1`,
+        `$accum = 1.0`,
+    }
+}
+
+pattern prod_accum($accum, $factor) {
+    or {
+        `$accum *= $factor`,
+        `$accum = $accum * $factor`,
+        `$accum = $factor * $accum`,
+    }
+}
+
+for_statement(body=block(statements=[prod_accum(accum = $var, factor = $left)]), $left, $right) as $for where {
+    $for <: after prod_init(accum = $var) => .,
+    $left <: identifier(),
+    $import = `math`,
+    $import <: ensure_imported(),
+} => `math.prod($right)`
+```
+
+## Transforms for loop to `math.prod`
+
+
+```python
+n = 1
+for x in range(10):
+    n *= x
+
+n = 1.0
+for x in range(10):
+    n = n * x
+
+n = 1
+for x in range(10):
+    n = x * n
+
+prod = 1
+for x in [4, 5, 6]:
+    prod *= x
+
+# Left as is
+
+n = 1
+for x in range(10):
+    y = n * x
+
+n = 1
+for x in range(10):
+    n = y * x
+
+n = 1
+for x in range(10):
+    n *= x
+    print("multiplied")
+```
+
+```python
+import math
+
+
+math.prod(range(10))
+
+
+math.prod(range(10))
+
+
+math.prod(range(10))
+
+
+math.prod([4, 5, 6])
+
+# Left as is
+
+n = 1
+for x in range(10):
+    y = n * x
+
+n = 1
+for x in range(10):
+    n = y * x
+
+n = 1
+for x in range(10):
+    n *= x
+    print("multiplied")
+```