he-029

# HumanEval/29

Implement a file **`solution.py`** that completes the function below. Keep the given name and signature; your file must define it at module level.

```python
from typing import List


def filter_by_prefix(strings: List[str], prefix: str) -> List[str]:
    """ Filter an input list of strings only for ones that start with a given prefix.
    >>> filter_by_prefix([], 'a')
    []
    >>> filter_by_prefix(['abc', 'bcd', 'cde', 'array'], 'a')
    ['abc', 'array']
    """
```

<!-- imported from OpenAI HumanEval (HumanEval/29) -->

# Auto-generated from OpenAI HumanEval HumanEval/29. Do not edit by hand.
from solution import *  # noqa: F401,F403 (prompt helpers may be referenced by tests)
from solution import filter_by_prefix as candidate

METADATA = {
    'author': 'jt',
    'dataset': 'test'
}


def check(candidate):
    assert candidate([], 'john') == []
    assert candidate(['xxx', 'asd', 'xxy', 'john doe', 'xxxAAA', 'xxx'], 'xxx') == ['xxx', 'xxxAAA', 'xxx']


def test_he_029():
    check(candidate)

You are an expert programmer. Solve the task exactly as specified. Output your solution as fenced code blocks using the required file name(s) and the exact function/type signatures requested. Prefer correctness; do not include prose outside code unless asked.

```python
from typing import List


def filter_by_prefix(strings: List[str], prefix: str) -> List[str]:
    """ Filter an input list of strings only for ones that start with a given prefix.
    >>> filter_by_prefix([], 'a')
    []
    >>> filter_by_prefix(['abc', 'bcd', 'cde', 'array'], 'a')
    ['abc', 'array']
    """
    return [s for s in strings if s.startswith(prefix)]
```

The user wants me to implement a function `filter_by_prefix` that filters a list of strings, keeping only those that start with a given prefix.

This is straightforward - I need to use the `str.startswith()` method or check if the string begins with the prefix.

Let me write the solution:

```python
from typing import List


def filter_by_prefix(strings: List[str], prefix: str) -> List[str]:
    """ Filter an input list of strings only for ones that start with a given prefix.
    >>> filter_by_prefix([], 'a')
    []
    >>> filter_by_prefix(['abc', 'bcd', 'cde', 'array'], 'a')
    ['abc', 'array']
    """
    return [s for s in strings if s.startswith(prefix)]
```

This is simple and correct. Let me verify with the examples:
- `filter_by_prefix([], 'a')` → `[]` ✓
- `filter_by_prefix(['abc', 'bcd', 'cde', 'array'], 'a')` → `['abc', 'array']` ✓