Python and Dataframe

Hi. I am a new Python user. I want to create a new variable New_variable in the following dataset. The rule for the New_variable is: if a consequential row started within 1 or less from any previous rows' Start or End variables' values, then it should have value the same otherwise incrementally increase by 1. ID Start End New_variable A 1 1 1 A 0.8 8 1 A 4 4 1 A 18 19 2 B 1 1 1 B 4 6 2 Next when add new observations, it also should have the same rule as above, but it should not change the previous New_variable-s values, but add consequentially even the Start value is smaller than the very first start value, see below the desired output. ID Start End A -5 0 A 6 6 A 10 11 A 23 23 C 1 2 The desired output should be as below: ID Start End New_variable A -5 0 3 A 1 1 1 A 0.8 8 1 A 4 4 1 A 6 6 1 A 10 11 4 A 18 19 2 A 23 23 5 B 1 1 1 B 4 6 2 C 1 2 1