1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
// Copyright (c) 2017-present PyO3 Project and Contributors
//
// based on Daniel Grunwald's https://github.com/dgrunwald/rust-cpython

use crate::{ffi, AsPyPointer, PyAny, PyDowncastError, PyErr, PyNativeType, PyResult, Python};

/// A Python iterator object.
///
/// Unlike other Python objects, this class includes a `Python<'p>` token
/// so that `PyIterator` can implement the Rust `Iterator` trait.
///
/// # Example
///
/// ```rust
/// # use pyo3::prelude::*;
/// use pyo3::types::PyIterator;
///
/// # fn main() -> PyResult<()> {
/// let gil = Python::acquire_gil();
/// let py = gil.python();
/// let list = py.eval("iter([1, 2, 3, 4])", None, None)?;
/// let numbers: PyResult<Vec<usize>> = list.iter()?.map(|i| i.and_then(PyAny::extract::<usize>)).collect();
/// let sum: usize = numbers?.iter().sum();
/// assert_eq!(sum, 10);
/// # Ok(())
/// # }
/// ```
pub struct PyIterator<'p>(&'p PyAny);

impl<'p> PyIterator<'p> {
    /// Constructs a `PyIterator` from a Python iterator object.
    pub fn from_object<T>(py: Python<'p>, obj: &T) -> Result<PyIterator<'p>, PyDowncastError>
    where
        T: AsPyPointer,
    {
        unsafe {
            let ptr = ffi::PyObject_GetIter(obj.as_ptr());
            // Returns NULL if an object cannot be iterated.
            if ptr.is_null() {
                PyErr::fetch(py);
                return Err(PyDowncastError);
            }

            if ffi::PyIter_Check(ptr) != 0 {
                // This looks suspicious, but is actually correct. Even though ptr is an owned
                // reference, PyIterator takes ownership of the reference and decreases the count
                // in its Drop implementation.
                //
                // Therefore we must use from_borrowed_ptr instead of from_owned_ptr so that the
                // GILPool does not take ownership of the reference.
                Ok(PyIterator(py.from_borrowed_ptr(ptr)))
            } else {
                Err(PyDowncastError)
            }
        }
    }
}

impl<'p> Iterator for PyIterator<'p> {
    type Item = PyResult<&'p PyAny>;

    /// Retrieves the next item from an iterator.
    ///
    /// Returns `None` when the iterator is exhausted.
    /// If an exception occurs, returns `Some(Err(..))`.
    /// Further `next()` calls after an exception occurs are likely
    /// to repeatedly result in the same exception.
    fn next(&mut self) -> Option<Self::Item> {
        let py = self.0.py();

        match unsafe { py.from_owned_ptr_or_opt(ffi::PyIter_Next(self.0.as_ptr())) } {
            Some(obj) => Some(Ok(obj)),
            None => {
                if PyErr::occurred(py) {
                    Some(Err(PyErr::fetch(py)))
                } else {
                    None
                }
            }
        }
    }
}

/// Dropping a `PyIterator` instance decrements the reference count on the object by 1.
impl<'p> Drop for PyIterator<'p> {
    fn drop(&mut self) {
        unsafe { ffi::Py_DECREF(self.0.as_ptr()) }
    }
}

#[cfg(test)]
mod tests {
    use crate::gil::GILPool;
    use crate::instance::AsPyRef;
    use crate::types::{PyDict, PyList};
    use crate::GILGuard;
    use crate::Python;
    use crate::ToPyObject;
    use indoc::indoc;

    #[test]
    fn vec_iter() {
        let gil_guard = Python::acquire_gil();
        let py = gil_guard.python();
        let obj = vec![10, 20].to_object(py);
        let inst = obj.as_ref(py);
        let mut it = inst.iter().unwrap();
        assert_eq!(10, it.next().unwrap().unwrap().extract().unwrap());
        assert_eq!(20, it.next().unwrap().unwrap().extract().unwrap());
        assert!(it.next().is_none());
    }

    #[test]
    fn iter_refcnt() {
        let obj;
        let count;
        {
            let gil_guard = Python::acquire_gil();
            let py = gil_guard.python();
            obj = vec![10, 20].to_object(py);
            count = obj.get_refcnt(py);
        }

        {
            let gil_guard = Python::acquire_gil();
            let py = gil_guard.python();
            let inst = obj.as_ref(py);
            let mut it = inst.iter().unwrap();

            assert_eq!(10, it.next().unwrap().unwrap().extract().unwrap());
        }
        assert_eq!(count, obj.get_refcnt(Python::acquire_gil().python()));
    }

    #[test]
    fn iter_item_refcnt() {
        let gil_guard = Python::acquire_gil();
        let py = gil_guard.python();

        let obj;
        let none;
        let count;
        {
            let _pool = unsafe { GILPool::new() };
            let l = PyList::empty(py);
            none = py.None();
            l.append(10).unwrap();
            l.append(&none).unwrap();
            count = none.get_refcnt(py);
            obj = l.to_object(py);
        }

        {
            let _pool = unsafe { GILPool::new() };
            let inst = obj.as_ref(py);
            let mut it = inst.iter().unwrap();

            assert_eq!(10, it.next().unwrap().unwrap().extract().unwrap());
            assert!(it.next().unwrap().unwrap().is_none());
        }
        assert_eq!(count, none.get_refcnt(py));
    }

    #[test]
    fn fibonacci_generator() {
        let fibonacci_generator = indoc!(
            r#"
            def fibonacci(target):
                a = 1
                b = 1
                for _ in range(target):
                    yield a
                    a, b = b, a + b
        "#
        );

        let gil = GILGuard::acquire();
        let py = gil.python();

        let context = PyDict::new(py);
        py.run(fibonacci_generator, None, Some(context)).unwrap();

        let generator = py.eval("fibonacci(5)", None, Some(context)).unwrap();
        for (actual, expected) in generator.iter().unwrap().zip(&[1, 1, 2, 3, 5]) {
            let actual = actual.unwrap().extract::<usize>().unwrap();
            assert_eq!(actual, *expected)
        }
    }
}