Generate Descriptive Statistics For Each Row Value And Transpose Dynamically

I have a dataframe like as shown below

df = pd.DataFrame({
'subject_id':[1,1,1,1,2,2,2,2,3,3,4,4,4,4,4],
'readings' : ['READ_1','READ_2','READ_1','READ_3','READ_1','READ_5','READ_6','READ_8','READ_10','READ_12','READ_11','READ_14','READ_09','READ_08','READ_07'],
'val' :[5,6,7,11,5,7,16,12,13,56,32,13,45,43,46],
})

What I would like to do is get the descriptive statistics/summarized form of existing columns instead of having the original columns. I expect to see (min,max,25%,75%,std,var) as new columns for each subject

I tried the below but the output isn't exact

df.groupby(['subject_id','readings']).describe().reset_index()   #this gives some output but it isn't exact
df.groupby(['subject_id','readings']).pivot_table(values='val', index='subject_id', columns='readings').describe()  # this throws error

I expect my output to be like as shown below. Basically it will be a wide and sparse matrix. Since the screenshot is wide, I couldn't enlarge it further. If you click on the image, you will have a better display of the expected output

Use Series.unstack for reshape after describe, then DataFrame.swaplevel and for order like in original add DataFrame.reindex:

df = (df.groupby(['subject_id','readings'])['val']
        .describe()
        .unstack()
        .swaplevel(0,1,axis=1)
        .reindex(df['readings'].unique(), axis=1, level=0))
df.columns = df.columns.map('_'.join)
df = df.reset_index()
print (df)

   subject_id  READ_1_count  READ_1_mean  READ_1_std  READ_1_min  READ_1_25%  \
0           1           2.0          6.0    1.414214         5.0         5.5   
1           2           1.0          5.0         NaN         5.0         5.0   
2           3           NaN          NaN         NaN         NaN         NaN   
3           4           NaN          NaN         NaN         NaN         NaN   

   READ_1_50%  READ_1_75%  READ_1_max  READ_2_count  ...  READ_08_75%  \
0         6.0         6.5         7.0           1.0  ...          NaN   
1         5.0         5.0         5.0           NaN  ...          NaN   
2         NaN         NaN         NaN           NaN  ...          NaN   
3         NaN         NaN         NaN           NaN  ...         43.0   

   READ_08_max  READ_07_count  READ_07_mean  READ_07_std  READ_07_min  \
0          NaN            NaN           NaN          NaN          NaN   
1          NaN            NaN           NaN          NaN          NaN   
2          NaN            NaN           NaN          NaN          NaN   
3         43.0            1.0          46.0          NaN         46.0   

   READ_07_25%  READ_07_50%  READ_07_75%  READ_07_max  
0          NaN          NaN          NaN          NaN  
1          NaN          NaN          NaN          NaN  
2          NaN          NaN          NaN          NaN  
3         46.0         46.0         46.0         46.0  

[4 rows x 105 columns]