Optimize _parse_and_collect_imports

The optimization achieves a **68% runtime improvement** (23.5ms → 14.0ms) by replacing the expensive `ast.walk()` traversal with a targeted recursive collection strategy.

**Key Performance Improvement:**

The original code uses `ast.walk(tree)` which visits **every single node** in the AST tree (12,947 hits shown in line profiler), consuming 71.7% of total runtime. This includes unnecessary nodes like expressions, literals, and operators that can never contain `ImportFrom` statements.

The optimized version implements a custom `collect_imports()` function that:
1. **Only traverses module body and control flow structures** where imports can legally appear (function/class definitions, if/while/for blocks, try/except)
2. **Skips irrelevant AST nodes** like expressions, literals, and operators entirely
3. **Recursively processes nested bodies** (body, orelse, finalbody, handlers) in a depth-first manner

**Why This Works:**

In Python, `from X import Y` statements can only appear:
- At module level
- Inside function/class definitions
- Within control flow blocks (if/while/for/try)

By checking `isinstance()` for only these container node types and recursively descending into their body attributes, we avoid traversing the entire AST subtree for each construct. This dramatically reduces the number of nodes visited while maintaining correctness.

**Test Case Performance:**

The optimization excels across all scales:
- **Small imports** (single statements): 60-77% faster
- **Large import lists** (100-500 items): 74-104% faster  
- **Many code blocks** (500-1000 lines): 70-77% faster
- **Mixed code/imports** at scale: 70% faster

The performance gain is particularly pronounced when the AST contains large amounts of non-import code (functions, classes, expressions), as shown by the `test_mixed_imports_and_code_large_scale` case improving from 9.31ms to 5.45ms (70.8% faster).

**Impact on Workloads:**

Given the function_references show this is used in code context extraction benchmarks, this optimization will significantly speed up any workflow that analyzes Python imports from large codebases or performs repeated import analysis during development workflows.

Author: codeflash-ai[bot]

codeflash/languages/python/context/code_context_extractor.py

@@ -553,12 +553,31 @@ def _parse_and_collect_imports(code_context: CodeStringsMarkdown) -> tuple[ast.M
     except SyntaxError:
         return None
     imported_names: dict[str, str] = {}
-    for node in ast.walk(tree):
-        if isinstance(node, ast.ImportFrom) and node.module:
-            for alias in node.names:
-                if alias.name != "*":
-                    imported_name = alias.asname if alias.asname else alias.name
-                    imported_names[imported_name] = node.module
+    
+    # Directly iterate over the module body and nested structures instead of ast.walk
+    # This avoids traversing every single node in the tree
+    def collect_imports(nodes):
+        for node in nodes:
+            if isinstance(node, ast.ImportFrom) and node.module:
+                for alias in node.names:
+                    if alias.name != "*":
+                        imported_name = alias.asname if alias.asname else alias.name
+                        imported_names[imported_name] = node.module
+            # Recursively check nested structures (function defs, class defs, if statements, etc.)
+            elif isinstance(node, (ast.FunctionDef, ast.AsyncFunctionDef, ast.ClassDef, 
+                                   ast.If, ast.For, ast.AsyncFor, ast.While, ast.With, 
+                                   ast.AsyncWith, ast.Try, ast.ExceptHandler)):
+                if hasattr(node, 'body'):
+                    collect_imports(node.body)
+                if hasattr(node, 'orelse'):
+                    collect_imports(node.orelse)
+                if hasattr(node, 'finalbody'):
+                    collect_imports(node.finalbody)
+                if hasattr(node, 'handlers'):
+                    for handler in node.handlers:
+                        collect_imports(handler.body)
+    
+    collect_imports(tree.body)
     return tree, imported_names