Pandas's regular expression function result is so strange

[cools0607]

I am trying to make a regular express for df1(dataframe).
I want to remove the expression related NOPOP.NoPop and NONPOP information in 3rd column.
In order to achieve quick search, I put 3rd column as a index of dataframe.
And operated it in "df.filter" way with regex.

import pandas as pd
k=[['a','b','c','NOPOP'],['d','e','f','POP'],['g','h','i','j'],['k','l','m','Pop'],['n','o','p','NoPop_AA'],['q','r','s','NONPOP']]
df_exp=pd.DataFrame(k)
df1=df_exp.set_index([3])
df2=df1.filter(regex='[^NOPOP]|[^NoPop]|[^NONPOP]', axis=0)

Output:
Out[263]: 
          0  1  2
3                
NOPOP     a  b  c
POP       d  e  f
j         g  h  i
Pop       k  l  m
NoPop_AA  n  o  p
NONPOP    q  r  s

The result did not delete "NOPOP.NoPop and NONPOP" related information, why not?


my desire output is just like below

Output:
          0  1  2
3        
POP       d  e  f
j         g  h  i
Pop       k  l  m