我想知道在Python中创建决策树（ID3）的步骤是什么？看起来如下的东西？ （如果不是其他的话，或者它比那更好吗？）另外，为了创建像下面这样的ID3树，我应该计算熵？怎么样？
thal = fixed_defect [4 6]
| ca <= 0.500000 [4 0]: negative
| ca > 0.500000 [0 6]: positive
thal = normal [84 19]
| thalach <= 111.500000 [0 4]: positive
| thalach > 111.500000 [84 15]
| | age <= 55.500000 [56 4]
| | | trestbps <= 113.500000 [9 3]
| | | | oldpeak <= 0.300000 [3 3]
| | | | | cp = typ_angina [0 0]: negative
| | | | | cp = asympt [0 2]: positive
| | | | | cp = non_anginal [1 1]
| | | | | | age <= 44.000000 [1 0]: negative
| | | | | | age > 44.000000 [0 1]: positive
| | | | | cp = atyp_angina [2 0]: negative
| | | | oldpeak > 0.300000 [6 0]: negative
| | | trestbps > 113.500000 [47 1]
| | | | oldpeak <= 3.550000 [47 0]: negative
| | | | oldpeak > 3.550000 [0 1]: positive
| | age > 55.500000 [28 11]
| | | chol <= 248.500000 [14 1]
| | | | oldpeak <= 2.800000 [14 0]: negative
| | | | oldpeak > 2.800000 [0 1]: positive
| | | chol > 248.500000 [14 10]
| | | | sex = female [13 3]
| | | | | cp = typ_angina [1 0]: negative
| | | | | cp = asympt [3 3]
| | | | | | age <= 58.000000 [2 0]: negative
| | | | | | age > 58.000000 [1 3]
| | | | | | | chol <= 362.000000 [0 3]: positive
| | | | | | | chol > 362.000000 [1 0]: negative
| | | | | cp = non_anginal [7 0]: negative
| | | | | cp = atyp_angina [2 0]: negative
| | | | sex = male [1 7]
| | | | | age <= 65.500000 [0 5]: positive
| | | | | age > 65.500000 [1 2]
| | | | | | age <= 66.500000 [1 0]: negative
| | | | | | age > 66.500000 [0 2]: positive
thal = reversable_defect [20 67]
| cp = typ_angina [3 1]
| | oldpeak <= 0.700000 [0 1]: positive
| | oldpeak > 0.700000 [3 0]: negative
| cp = asympt [5 53]
| | oldpeak <= 0.650000 [5 10]
| | | chol <= 240.500000 [5 2]
| | | | chol <= 192.000000 [1 2]
| | | | | age <= 62.000000 [0 2]: positive
| | | | | age > 62.000000 [1 0]: negative
| | | | chol > 192.000000 [4 0]: negative
| | | chol > 240.500000 [0 8]: positive
| | oldpeak > 0.650000 [0 43]: positive
| cp = non_anginal [9 10]
| | oldpeak <= 1.900000 [9 5]
| | | trestbps <= 122.500000 [6 0]: negative
| | | trestbps > 122.500000 [3 5]
| | | | chol <= 232.500000 [3 1]
| | | | | trestbps <= 129.000000 [0 1]: positive
| | | | | trestbps > 129.000000 [3 0]: negative
| | | | chol > 232.500000 [0 4]: positive
| | oldpeak > 1.900000 [0 5]: positive
| cp = atyp_angina [3 3]
| | age <= 47.000000 [2 0]: negative
| | age > 47.000000 [1 3]
| | | trestbps <= 109.000000 [1 0]: negative
| | | trestbps > 109.000000 [0 3]: positive