Because Python automatically understands the data type when you assign a value to it and there's no need to determine whether the data type is integer or float or string.
A = 7 #No need to write int A
B = 7.5 #No need to write float B
C = "Hi" #No need to write string C
Variables generally have a data type when they are a assigned to a certain value. The data type of variable can be found by the type of value assigning to it.
eg:-We calls different variables as numeric variables as they are assigned to numeric value.(n=5.1 , n is a numeric variable as the float value is assigned to it).