Pandas - How to replace string values in a column with integer numbers

I found this nice solution on StackOverflow to the problem of replacing strings in the columns of a dataframe. Lets assume that a column named labels contains the label strings [A,B,C] and we want to replace them with [0,1,2]. Then we can do the following,

labels = df['labels'].unique().tolist()
mapping = dict( zip(labels,range(len(labels))) )
df.replace({'labels': mapping},inplace=True)

This code first creates a list of the unique labels, after that it creates a dictionary mapping from label value to a numeric value, and finally does a in place replacing of the label values with the numerical values.