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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"py/with macro doesn't bind the return value of __enter__ method","articleBody":"The `py/with` macro implementation doesn't correctly follow Python's `with` statement semantics. According to the [Python documentation](https://docs.python.org/3/reference/compound_stmts.html#the-with-statement), the value bound in a `with` statement should be the return value of calling `__enter__()` on the context manager:\n\n```python\nmanager = (EXPRESSION)\nenter = type(manager).__enter__\nexit = type(manager).__exit__\nvalue = enter(manager)  # This value should be bound to TARGET\nhit_except = False\n\ntry:\n    TARGET = value  # TARGET gets the return value of enter(manager)\n    SUITE\n...\n```\n\n**Current Implementation**\n\nThe current macro ([with.clj#L45-L63](https://github.com/clj-python/libpython-clj/blob/7f572215a96ac6fb14b5928ee6258b889cdee375/src/libpython_clj2/python/with.clj#L45C1-L63C60)) calls `__enter__` but discards its return value:\n\n```clojure\n(py-fn/call-attr ~varname \"__enter__\" nil)  ; Return value is ignored\n(try\n  (let [retval# (do ~@body)]\n    ...\n```\n\n**Expected Behavior**\n\nThe bound variable should receive the return value of `__enter__()`, not the context manager itself:\n\n```clojure\n(let [enter-result# (py-fn/call-attr ~varname \"__enter__\" nil)]\n  (try\n    (let [~varname enter-result#  ; Rebind to __enter__'s return value\n          retval# (do ~@body)]\n      ...\n```\n\n**Why Current Tests Pass**\n\nThe existing test in [python_test.clj#L167](https://github.com/clj-python/libpython-clj/blob/master/test/libpython_clj2/python_test.clj#L167) uses a `WithObjClass` where `__enter__()` returns `None` (implicitly), and the test methods are called on the original object. This masks the bug.\n\n**Real-World Example**\n\nA common Python pattern that fails with the current implementation:\n\n```python\nwith open('file.txt', 'r') as f:\n    content = f.read()  # f should be the file object returned by __enter__\n```\n\nWith the current macro, `f` would be bound to the unopened file path/manager rather than the file object returned by `__enter__()`.\n\n**Next Steps**\n\n1. Add test cases that verify this behavior (e.g., update `WithObjClass.__enter__` to return a different object, or test with Python's built-in file context manager)\n2. Update the macro to correctly bind the return value of `__enter__()`","author":{"url":"https://github.com/lidorcg","@type":"Person","name":"lidorcg"},"datePublished":"2025-11-10T16:57:54.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":0},"url":"https://github.com/273/libpython-clj/issues/273"}