he-007

# HumanEval/7

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_substring(strings: List[str], substring: str) -> List[str]:
    """ Filter an input list of strings only for ones that contain given substring
    >>> filter_by_substring([], 'a')
    []
    >>> filter_by_substring(['abc', 'bacd', 'cde', 'array'], 'a')
    ['abc', 'bacd', 'array']
    """
```

<!-- imported from OpenAI HumanEval (HumanEval/7) -->

# Auto-generated from OpenAI HumanEval HumanEval/7. Do not edit by hand.
from solution import *  # noqa: F401,F403 (prompt helpers may be referenced by tests)
from solution import filter_by_substring 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']
    assert candidate(['xxx', 'asd', 'aaaxxy', 'john doe', 'xxxAAA', 'xxx'], 'xx') == ['xxx', 'aaaxxy', 'xxxAAA', 'xxx']
    assert candidate(['grunt', 'trumpet', 'prune', 'gruesome'], 'run') == ['grunt', 'prune']


def test_he_007():
    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_substring(strings: List[str], substring: str) -> List[str]:
    """ Filter an input list of strings only for ones that contain given substring
    >>> filter_by_substring([], 'a')
    []
    >>> filter_by_substring(['abc', 'bacd', 'cde', 'array'], 'a')
    ['abc', 'bacd', 'array']
    """
    return [s for s in strings if substring in s]
```

The task is to implement a function that filters a list of strings to only include those that contain a given substring.

Looking at the examples:
- `filter_by_substring([], 'a')` returns `[]` (empty list)
- `filter_by_substring(['abc', 'bacd', 'cde', 'array'], 'a')` returns `['abc', 'bacd', 'array']`

So I need to:
1. Iterate through the list of strings
2. Check if each string contains the substring
3. Return a new list with only the strings that contain the substring

The simplest way to check if a string contains a substring in Python is using the `in` operator.

Let me write the solution:

```python
from typing import List


def filter_by_substring(strings: List[str], substring: str) -> List[str]:
    """ Filter an input list of strings only for ones that contain given substring
    >>> filter_by_substring([], 'a')
    []
    >>> filter_by_substring(['abc', 'bacd', 'cde', 'array'], 'a')
    ['abc', 'bacd', 'array']
    """
    return [s for s in strings if substring in s]
```

This is a clean, Pythonic solution using list comprehension. It checks if the substring is in each string and includes it in the result if true.