freeCodeCamp/curriculum/challenges/chinese/08-data-analysis-with-python/data-analysis-with-python-course/data-cleaning-introduction.md

id	challengeType	videoId
5e9a093a74c4063ca6f7c15d	11	ovYNhnltVxY

Description

More resources: - Notebook

Tests

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