python - pandas set one column equal to 1 but both df changes -

i'm trying df b column d 1, however, when run code, changes df a column d 1 also... why that, why variables linked? , how change df b only?

import pandas pd, os, numpy np df = pd.dataframe(np.random.randint(0,100,size=(100, 4)), columns=list('abcd')) a=df b=df b['d']=1 

output:

>>>       b   c  d 0  98  84   3  1 1  13  35  76  1 2  17  84  28  1 3  22   9  41  1 4  54   3  20  1 >>> b       b   c  d 0  98  84   3  1 1  13  35  76  1 2  17  84  28  1 3  22   9  41  1 4  54   3  20  1 >>>  

a, b , df references same object. when change b['d'], changing column of actual object. instead, looks want copy dataframe:

import pandas pd, os, numpy np df = pd.dataframe(np.random.randint(0,100,size=(100, 4)), columns=list('abcd')) a=df.copy() b=df.copy() b['d']=1 

which yields

b.head() out:        b   c  d 0  63  52  92  1 1  98  35  43  1 2  24  87  70  1 3  38   4   7  1 4  71  30  25  1  a.head() out:        b   c   d 0  63  52  92  80 1  98  35  43  78 2  24  87  70  26 3  38   4   7  48 4  71  30  25  61 

there detailed responses here.