def make_ewm_features(cols_roll, ewm_alpha, df_input):
	"""
	Make mean ewm features based on cols_roll, ewm_alpha.
	Make std ewm features for 'playMin'. 
	Return list of column names containing all the ewm features created.

	Parameters:
	-----------
	cols_roll -- (list) a list of column names used to make ewm features
	ewm_alpha -- (list) a list of numbers used as the alpha for makign ewm features
	df_input -- (pd DataFrame) the input dataframe which contains the features used for making ewm features
	
	Return:
	-----------
	cols_created_ewm -- (list) a list of column names of the created ewm features
	df_output -- (pd DataFrame) the output dataframe containing all the ewm features
	"""
	cols_created_ewm = []
	df_output = df_input.copy()
	for col in cols_roll:
		for alpha in ewm_alpha:
			new_col_mean = col+'_ewm_0'+str(alpha-int(alpha))[2:] # create ewm feature name
			cols_created_ewm.append(new_col_mean)
			df_output.loc[:, new_col_mean] = df_input[col].ewm(alpha=alpha, min_periods=1).mean()
			
			if col == 'playMin':
				new_col_std = col+'_ewm_std_0'+str(alpha-int(alpha))[2:] # create ewm feature name
				df_output.loc[:, new_col_std] = df_input[col].ewm(alpha=alpha, min_periods=1).std()
				cols_created_ewm.append(new_col_std)
	
	return cols_created_ewm, df_output