How can I get the number of the row in a dataframe that contains a certain value in a certain column using Pandas? For example, I have the following dataframe:

     ClientID  LastName
0    34        Johnson
1    67        Smith
2    53        Brows  

How can I find the number of the row that has 'Smith' in 'LastName' column?

To get all indices that matches 'Smith'

>>> df[df['LastName'] == 'Smith'].index
Int64Index([1], dtype='int64')

or as a numpy array

>>> df[df['LastName'] == 'Smith'].index.to_numpy()  # .values on older versions
array([1])

or if there is only one and you want the integer, you can subset

>>> df[df['LastName'] == 'Smith'].index[0]
1

You could use the same boolean expressions with .loc, but it is not needed unless you also want to select a certain column, which is redundant when you only want the row number/index.