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Use size_hint in PyArray::from_iter. #121

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Merged
merged 1 commit into from
Nov 16, 2019
Merged

Use size_hint in PyArray::from_iter. #121

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12 changes: 7 additions & 5 deletions src/array.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -743,8 +743,8 @@ impl<T: TypeNum> PyArray<T, Ix1> {
/// Construct one-dimension PyArray from a type which implements
/// [`IntoIterator`](https://doc.rust-lang.org/std/iter/trait.IntoIterator.html).
///
/// This method can allocate memory multiple times and not fast.
/// When you can use [from_exact_iter](method.from_exact_iter.html), we recommend to use it.
/// If no reliable [`size_hint`](https://doc.rust-lang.org/std/iter/trait.Iterator.html#method.size_hint) is available,
/// this method can allocate memory multiple time, which can hurt performance.
///
/// # Example
/// ```
Expand All @@ -758,13 +758,15 @@ impl<T: TypeNum> PyArray<T, Ix1> {
/// # }
/// ```
pub fn from_iter(py: Python<'_>, iter: impl IntoIterator<Item = T>) -> &Self {
let mut capacity = 512 / mem::size_of::<T>();
let iter = iter.into_iter();
let (min_len, max_len) = iter.size_hint();
let mut capacity = max_len.unwrap_or(min_len.max(512 / mem::size_of::<T>()));
let array = Self::new(py, [capacity], false);
let mut length = 0;
unsafe {
for (i, item) in iter.into_iter().enumerate() {
for (i, item) in iter.enumerate() {
length += 1;
if length >= capacity {
if length > capacity {
capacity *= 2;
array
.resize(capacity)
Expand Down