if：实现对空间的划分（partition）；if 与随机数相结合表达概率；
1. 分段函数与 if else
例1：对[0, 1]区间均匀分布 cdf 函数的模拟
def uniform_cdf(x):if x < 0: return 0 # x < 0elif x < 1: return x # 0 <= x < 1else: return 1# x >= 1
2. while (A && B)
双条件满足才执行，单个条件不满足就退出；
epochs, done_looping = 1000, Falseepoch = 0while (epoch < epochs) and (not done_looping):epoch += 1...if ...:done_looping = Truebreak...
3. 阈值与双重 if
比如，如果这次的改进较上次优化了 %5 以上，则：
best_valid_loss = np.infimprovement_thresh = 0.95patience, patience_inc = 5000, 2for iter in range(n_iters):... if this_valid_loss < best_valid_loss:if this_valid_loss < best_valid_loss * improvement_thresh:patience = max(patience, iter*patience_inc)best_valid_loss = this_valid_loss
