笛卡尔积（评估表达式实现）

A × B = ( < x , y > ∣ x ∈ A ∧ y ∈ B ) A \times B = \left( <x,y> | x \in A ∧ y \in B \right) A×B=(<x,y>∣x∈A∧y∈B)

考虑到递归也好，还是别的方法，没办法在效率方面达到一个比较好的均衡，于是用推符号语句然后评估表达式的方式实现了这样的笛卡尔积

A = list(range(4))
B = [chr(i) for i in range(65,65+4)]
A,B

def productExpr(*D,typekey='python'):
    m = len(D)
    symbol_index = {i:chr(i) for i in range(97,97+m)}
    symbol1 = "".join(["{}{}{}{}{}".format(" for " ,symbol_index[i]," in D[" ,i-97,"] ") for i in symbol_index])
    symbol2 = "".join(["{}{}".format(",",symbol_index[i]) for i in symbol_index])[1:]
    temp_expression = "{}{}{}{}{}{}".format("{","(",symbol2,")",symbol1,"}").replace("D",str(D))
    if typekey == "numpy": 
        expression = "{}{}{}".format("np.array(list(",temp_expression,"))")
    elif typekey == "python":
        expression = temp_expression
    expr = eval(expression)
    return expr

python set结构

numpy 结构

本文地址：https://blog.csdn.net/weixin_43069769/article/details/107158272