[USER (data scientist)]: Thanks a bunch! How about a histogram for player rankings distribution? Please generate and display a histogram showing the distribution of player rankings in the ATP tennis dataset.
My template of code snippet is:

---BEGIN CODE TEMPLATE---

import pandas as pd
import matplotlib.pyplot as plt
import pickle

atp_tennis = pd.read_csv('atp_tennis.csv')

# YOUR SOLUTION BEGIN:
<code1>
[COMPLETE YOUR CODE] 
</code1>
# YOUR SOLUTION END

plt.savefig('./pred_result/hist_chart.png')
plt.show()

---END CODE TEMPLATE---

[YOU (AI assistant)]: No problem! Here's the code to create a histogram using matplotlib: 
'''
import pandas as pd
import matplotlib.pyplot as plt
import pickle

atp_tennis = pd.read_csv('atp_tennis.csv')

# YOUR SOLUTION BEGIN:
