无法将熊猫系列转换为DateTime

Question

我正在尝试将熊猫系列转换为Datetime格式，但是出现以下错误。

AttributeError: 'DataFrame' object has no attribute 'to_datetime'

我当前的代码是：

  import pandas as pd
    import numpy as np
    from datetime import datetime
    import matplotlib.pyplot as plt
    import matplotlib.dates as dates

    file = pd.ExcelFile('/Users/saif/Dropbox/Personal Health/Mega Sleep Data/Merged Database.xlsx')
    Sleep= file.parse('Sheet 1')  


Sleep.rename(columns={'levels/summary/deep/minutes': 'TotalDeepSleep', 'levels/summary/deep/thirtyDayAvgMinutes': 'AverageDeepSleep'}, inplace=True)

    ### converting dates to DateTime

    **Ω**

日期当前存储为：

print(Sleep['dateOfSleep'].head())
0    2018-07-02
1    2018-07-03
2    2018-07-04
3    2018-07-05
4    2018-07-07
Name: dateOfSleep, dtype: object