python - Pandas, Fill Boolean Value compare two row -

my data

             b 1   false   true 2   false   true 3   false   true 4   false   true 5    true  false 6    true  false 7   false   true 8    true  false 9    true   true 10  false   true 11  false   true 12  false   true 13   true  false 14   true  false 15  false  false 16  false  false 17  false  false 

my code

data.loc[(data['b']== false) & (data['b'].shift(1) == true), 'a'] = true data.loc[(data['a'].shift(1)== true) & (data['b'].shift(1) == false),'a'] = true 

my desire result row no. 15,16,17 true,

             b 1   false   true 2   false   true 3   false   true 4   false   true 5    true  false 6    true  false 7   false   true 8    true  false 9    true   true 10  false   true 11  false   true 12  false   true 13   true  false 14   true  false 15  **true**  false 16  **true**  false 17  **true**  false 

once 'a' "true" "true" before meet "b" "true" , "b" become "true" "a" turn "false"

is there simple solution solving this? in advance!!