---
id: 5e9a093a74c4063ca6f7c15d
title: Data Cleaning Introduction
challengeType: 11
isHidden: true
videoId: ovYNhnltVxY
---

## Description
<section id='description'>
</section>

## Tests
<section id='tests'>

```yml
question:
  text: |
    What will the following code print out?:

    ```py
    import pandas as pd
    import numpy as np

    s = pd.Series(['a', 3, np.nan, 1, np.nan])

    print(s.notnull().sum())
    ```

  answers:
    - '3'
    - |
      ```
      0     True
      1     True
      2    False
      3     True
      4    False
      dtype: bool
      ```
    - |
      ```
      0    False
      1    False
      2     True
      3    False
      4     True
      dtype: bool
      ```
  solution: 1
```

</section>