Return list[str] when passed multiple values from python

docs/dev-build.md

@@ -349,8 +349,72 @@ Python also often provides single functions which can receive multiple significa
         --8<-- "rust/fizzbuzzo3/src/lib.rs"
         ```
 
-!!! warning "`Union` type returns"
-    If you want to create something like: `#!python def fizzbuzz(n: int | list[int]) -> str | list[str]:` [Issue pyo3/#1637](https://github.com/PyO3/pyo3/issues/1637) suggests you may be able to do something with the `IntoPy` trait but I haven't tried (yet)
+!!! pyo3 "`Union` type returns: `#!python def fizzbuzz(n: int | list[int]) -> str | list[str]`"
+    If you would like to provide different return types for different cases:
+
+    1. Implement an `enum`, or a wrapper `struct` around an existing `enum`, that holds the different types.
+    1. Provide one or more conversion `From` traits to convert from the return of your core rust functions.
+    1. Provide a conversion [`IntoPy` trait](https://docs.rs/pyo3/latest/pyo3/conversion/trait.IntoPy.html) to convert to the relevant PyO3 types.
+    1. Use this new type as the return of your wrapped function.
+
+        In **`/rust/fizzbuzzo3/src/lib.rs`**:
+        ```rust
+        ...
+        struct FizzBuzzReturn(FizzBuzzAnswer);
+
+        impl From<FizzBuzzAnswer> for FizzBuzzReturn {
+            fn from(value: FizzBuzzAnswer) -> Self {
+                FizzBuzzReturn(value)
+            }
+        }
+
+        impl IntoPy<Py<PyAny>> for FizzBuzzReturn {
+            fn into_py(self, py: Python<'_>) -> Py<PyAny> {
+                match self.0 {
+                    FizzBuzzAnswer::One(string) => string.into_py(py),
+                    FizzBuzzAnswer::Many(list) => list.into_py(py),
+                }
+            }
+        }
+        ...
+        #[pyfunction]
+        #[pyo3(name = "fizzbuzz", text_signature = "(n)")]
+        fn py_fizzbuzz(num: FizzBuzzable) -> PyResult<FizzBuzzReturn> {
+            ...
+        ```
+
+        Thanks to the comments in [Issue pyo3/#1637](https://github.com/PyO3/pyo3/issues/1637) for pointers on how to get this working.
+
+    1. Add `@overload` hints for your IDE (see [IDE type & doc hinting](#ide-type-doc-hinting)), so that it understands the relationships between input and output types:
+
+        In **`/python/fizzbuzz/fizzbuzzo3.pyi`**:
+        ```python
+        ...
+        from typing import overload
+
+        @overload
+        def fizzbuzz(n: int) -> str:
+            ...
+
+        @overload
+        def fizzbuzz(n: list[int] | slice) -> list[str]:
+            ...
+
+        def fizzbuzz(n):
+            """
+            Returns the correct fizzbuzz answer for any number or list/range of numbers.
+            ...
+        ```
+
+    ??? pyo3 "**`rust/fizzbuzzo3/src/lib.rs`** - full source"
+        ```rust
+        --8<-- "rust/fizzbuzzo3/src/lib.rs"
+        ```
+
+    ??? python "**`python/fizzbuzz/fizzbuzzo3.pyi`** - full source"
+        ```python
+        --8<-- "python/fizzbuzz/fizzbuzzo3.pyi"
+        ```
 
 ## IDE type & doc hinting
 

python/fizzbuzz/fizzbuzzo3.pyi

@@ -10,7 +10,17 @@ Usage:
     ```
 """
 
-def fizzbuzz(n: int | list[int] | slice) -> str:
+from typing import overload
+
+@overload
+def fizzbuzz(n: int) -> str:
+    ...
+
+@overload
+def fizzbuzz(n: list[int] | slice) -> list[str]:
+    ...
+
+def fizzbuzz(n):
     """
     Returns the correct fizzbuzz answer for any number or list/range of numbers.
 
@@ -21,8 +31,8 @@ def fizzbuzz(n: int | list[int] | slice) -> str:
         n: the number(s) to fizzbuzz
 
     Returns:
-        A `str` with the correct fizzbuzz answer(s).
-        In the case of a list or range of inputs the answers will be separated by `, `
+        In the case of a single number: a `str` with the correct fizzbuzz answer.
+        In the case of a list or range of inputs: a `list` of `str` with the correct fizzbuzz answers.
 
     Examples:
         a single `int`:
@@ -37,18 +47,21 @@ def fizzbuzz(n: int | list[int] | slice) -> str:
         ```
         from fizzbuzz.fizzbuzzo3 import fizzbuzz
         >>> fizzbuzz([1,3])
-        '1, fizz'
+        ['1', 'fizz']
         ```
         a `slice` representing a range:
         ```
         from fizzbuzz.fizzbuzzo3 import fizzbuzz
         >>> fizzbuzz(slice(1,4,2))
-        '1, fizz'
+        ['1', 'fizz']
         >>> fizzbuzz(slice(1,4))
-        '1, 2, fizz'
+        ['1', '2', 'fizz']
         >>> fizzbuzz(slice(4,1,-1))
-        '4, fizz, 2'
+        ['4', 'fizz', '2']
+        >>> fizzbuzz(slice(1,5,-1))
+        []
         ```
         Note: Slices are inclusive on the left, exclusive on the right and can contain an optional step.
-        Negative steps require start > stop.
+        Negative steps require start > stop, positive steps require stop > start; other combinations return `[]`.
+        A step of zero is invalid and will raise a `ValueError`.
     """

rust/fizzbuzzo3/src/lib.rs

@@ -1,6 +1,6 @@
 use std::ops::Neg;
 
-use fizzbuzz::{FizzBuzz, MultiFizzBuzz};
+use fizzbuzz::{FizzBuzz, FizzBuzzAnswer, MultiFizzBuzz};
 use pyo3::{exceptions::PyValueError, prelude::*, types::PySlice};
 use rayon::iter::{IndexedParallelIterator, IntoParallelIterator, ParallelIterator};
 
@@ -25,6 +25,24 @@ impl IntoPy<Py<PyAny>> for MySlice {
     }
 }
 
+/// A wrapper struct for FizzBuzzAnswer to provide a custom implementation of `IntoPy`.
+struct FizzBuzzReturn(FizzBuzzAnswer);
+
+impl From<FizzBuzzAnswer> for FizzBuzzReturn {
+    fn from(value: FizzBuzzAnswer) -> Self {
+        FizzBuzzReturn(value)
+    }
+}
+
+impl IntoPy<Py<PyAny>> for FizzBuzzReturn {
+    fn into_py(self, py: Python<'_>) -> Py<PyAny> {
+        match self.0 {
+            FizzBuzzAnswer::One(string) => string.into_py(py),
+            FizzBuzzAnswer::Many(list) => list.into_py(py),
+        }
+    }
+}
+
 /// Returns the correct fizzbuzz answer for any number or list/range of numbers.
 ///
 /// This is an optimised algorithm compiled in rust. Large lists will utilise multiple CPU cores for processing.
@@ -34,8 +52,8 @@ impl IntoPy<Py<PyAny>> for MySlice {
 ///     n: the number(s) to fizzbuzz
 ///
 /// Returns:
-///     A `str` with the correct fizzbuzz answer(s).
-///     In the case of a list or range of inputs the answers will be separated by `, `
+///     In the case of a single number: a `str` with the correct fizzbuzz answer.
+///     In the case of a list or range of inputs: a `list` of `str` with the correct fizzbuzz answers.
 ///
 /// Examples:
 ///     a single `int`:
@@ -50,23 +68,27 @@ impl IntoPy<Py<PyAny>> for MySlice {
 ///     ```
 ///     from fizzbuzz.fizzbuzzo3 import fizzbuzz
 ///     >>> fizzbuzz([1,3])
-///     '1, fizz'
+///     ['1', 'fizz']
 ///     ```
 ///     a `slice` representing a range:
 ///     ```
 ///     from fizzbuzz.fizzbuzzo3 import fizzbuzz
 ///     >>> fizzbuzz(slice(1,4,2))
-///     '1, fizz'
+///     ['1', 'fizz']
 ///     >>> fizzbuzz(slice(1,4))
-///     '1, 2, fizz'
+///     ['1', '2', 'fizz']
 ///     >>> fizzbuzz(slice(4,1,-1))
-///     '4, fizz, 2'
+///     ['4', 'fizz', '2']
+///     >>> fizzbuzz(slice(1,5,-1))
+///     []
 ///     ```
 ///     Note: Slices are inclusive on the left, exclusive on the right and can contain an optional step.
-///     Negative steps require start > stop.
+///     Note: Slices are inclusive on the left, exclusive on the right and can contain an optional step.
+///     Negative steps require start > stop, positive steps require stop > start; other combinations return `[]`.
+///     A step of zero is invalid and will raise a `ValueError`.
 #[pyfunction]
 #[pyo3(name = "fizzbuzz", text_signature = "(n)")]
-fn py_fizzbuzz(num: FizzBuzzable) -> PyResult<String> {
+fn py_fizzbuzz(num: FizzBuzzable) -> PyResult<FizzBuzzReturn> {
     match num {
         FizzBuzzable::Int(n) => Ok(n.fizzbuzz().into()),
         FizzBuzzable::Float(n) => Ok(n.fizzbuzz().into()),
@@ -141,8 +163,15 @@ mod tests {
     #[pyo3import(py_fizzbuzzo3: from fizzbuzzo3 import fizzbuzz)]
     fn test_fizzbuzz_vec() {
         let input = vec![1, 2, 3, 4, 5];
-        let result: String = fizzbuzz!(input);
-        assert_eq!(result, "1, 2, fizz, 4, buzz");
+        let expected = vec![
+            "1".to_string(),
+            "2".to_string(),
+            "fizz".to_string(),
+            "4".to_string(),
+            "buzz".to_string(),
+        ];
+        let result: Vec<String> = fizzbuzz!(input);
+        assert_eq!(result, expected);
     }
 
     #[pyo3test]
@@ -160,8 +189,15 @@ mod tests {
             stop: 6,
             step: Some(1),
         };
-        let result: String = fizzbuzz!(input);
-        assert_eq!(result, "1, 2, fizz, 4, buzz");
+        let expected = vec![
+            "1".to_string(),
+            "2".to_string(),
+            "fizz".to_string(),
+            "4".to_string(),
+            "buzz".to_string(),
+        ];
+        let result: Vec<String> = fizzbuzz!(input);
+        assert_eq!(result, expected);
     }
 
     #[pyo3test]
@@ -172,8 +208,15 @@ mod tests {
             stop: 6,
             step: None,
         };
-        let result: String = fizzbuzz!(input);
-        assert_eq!(result, "1, 2, fizz, 4, buzz");
+        let expected = vec![
+            "1".to_string(),
+            "2".to_string(),
+            "fizz".to_string(),
+            "4".to_string(),
+            "buzz".to_string(),
+        ];
+        let result: Vec<String> = fizzbuzz!(input);
+        assert_eq!(result, expected);
     }
 
     #[pyo3test]
@@ -184,8 +227,9 @@ mod tests {
             stop: 6,
             step: Some(2),
         };
-        let result: String = fizzbuzz!(input);
-        assert_eq!(result, "1, fizz, buzz");
+        let expected = vec!["1".to_string(), "fizz".to_string(), "buzz".to_string()];
+        let result: Vec<String> = fizzbuzz!(input);
+        assert_eq!(result, expected);
     }
 
     #[pyo3test]
@@ -196,8 +240,9 @@ mod tests {
             stop: 0,
             step: Some(1),
         };
-        let result: String = fizzbuzz!(input);
-        assert_eq!(result, "");
+        let result: Vec<String> = fizzbuzz!(input);
+        let expected: Vec<String> = vec![];
+        assert_eq!(result, expected);
     }
 
     #[pyo3test]
@@ -208,8 +253,9 @@ mod tests {
             stop: 0,
             step: Some(-2),
         };
-        let result: String = fizzbuzz!(input);
-        assert_eq!(result, "buzz, fizz, 1");
+        let expected = vec!["buzz".to_string(), "fizz".to_string(), "1".to_string()];
+        let result: Vec<String> = fizzbuzz!(input);
+        assert_eq!(result, expected);
     }
 
     #[pyo3test]
@@ -220,8 +266,14 @@ mod tests {
             stop: 1,
             step: Some(-1),
         };
-        let result: String = fizzbuzz!(input);
-        assert_eq!(result, "buzz, 4, fizz, 2");
+        let expected = vec![
+            "buzz".to_string(),
+            "4".to_string(),
+            "fizz".to_string(),
+            "2".to_string(),
+        ];
+        let result: Vec<String> = fizzbuzz!(input);
+        assert_eq!(result, expected);
     }
 
     #[pyo3test]
@@ -232,8 +284,10 @@ mod tests {
             stop: 0,
             step: Some(-2),
         };
-        let result: String = fizzbuzz!(input);
-        assert_eq!(result, "fizz, 4, 2");
+
+        let expected = vec!["fizz".to_string(), "4".to_string(), "2".to_string()];
+        let result: Vec<String> = fizzbuzz!(input);
+        assert_eq!(result, expected);
     }
     #[pyo3test]
     #[allow(unused_macros)]