How to mutate the dataframe to add item mean and sd to each row

import pandas as pd

sample = pd.read_csv('./sampledata.csv')
sample.head(3)

	Movement	Island_Type	Island	Distance	Item	Sentence	Subj_id	List	Score
0	WH	whe	non	sh	1	Who thinks that Paul stole the necklace?	1	1	6
1	WH	whe	non	sh	2	Who thinks that Matt chased the bus?	1	1	2
2	WH	whe	non	sh	3	Who thinks that Tom sold the television?	1	1	3

I want to create new columns Score_mean and Score_sd, which show the mean and standard deviation of a particular item’s scores given by different subjects. Think group_by followed by mutate in R. Here’s one way to accomplish it.

sample = sample.assign(
    Score_mean = sample.groupby(['Sentence'])['Score'].transform('mean'),
    Score_sd = sample.groupby(['Sentence'])['Score'].transform('std'))

sample.head(3)

	Movement	Island_Type	Island	Distance	Item	Sentence	Subj_id	List	Score	Score_mean	Score_sd
0	WH	whe	non	sh	1	Who thinks that Paul stole the necklace?	1	1	6	4.875	1.543805
1	WH	whe	non	sh	2	Who thinks that Matt chased the bus?	1	1	2	4.250	1.914854
2	WH	whe	non	sh	3	Who thinks that Tom sold the television?	1	1	3	4.250	1.693123