Python 在列表中查找元素并返回 true 或 false

Question

I'm in stuck with a research elements in list of strings. I take a text with numbers(string) and I try to find symbols like '+' or '-' My code:

 Lista=np.array([s for s in text]) 
 y=np.where(Lista=='+') 
 if y==[]: /*so, if it's void*/
        print("any elements")
  else:
        print("yes")

I try to do this, because I'd like to create a calculator, and for this moment I can do just + operation (in second part of my code, I use split("+") and cast string to int). So I'd like to create with if, else, elif a struct similar to switch case. Something like: if ('+') -> do this operation, else if ('-')-> do this operation, ecc. Obviously, I'd like to create 4 y=np.where(lista='+'/='-'/=' '...) and for everyone create if else. So if in thirst case I don't find '+':pass. If in second case I don't find '-' :pass. If in third case I find ' ' : do the moltiplicato. This things I try to do with y==[] or y!=[]. When I print the results of y=np.where(lista='+'), so I see that it returns array[1] or array[], but if I try to make this as a condition, it doesn't work.

Example. In my calculator I wrote 4+5. 4+5 it's saved in a var called text. I convert the var text, in Lista=np.array([s for s in text]). After I try to search in Lista the symbol '+' with y=np.where(Lista=='+'). In console I see that it's at first position, so in array[1]. So with if condition

    if y==[]: 
       print("the list it's void") 
       pass
    else: print("the elemnt it's at firt position")
    Lista=np.array([s for s in text.split('+')])
    v=[int(v) for v in Lista]
    c=sum(v)
    print(c)

But, when I wrote 4+5, with the condition y==[] it's print that the list it's void, but it doesnt true because at arrayIndex I see that in position y[1] ther're a '+'.

Example in Java code. I'd like to have the same in Python public class Main {

    public static void main(String[] args) {
        boolean findSymbol=true;

        char [] p = {31, 28, 31, 30, 31, 30, 31, '-'};
        for (char c : p) {
            if (c == '+') {
                findSymbol= true;
                System.out.println("let's do something");
            } else
                findSymbol = false;
            System.out.println("Nope");

            if (c == '-') {
                findSymbol=true;
                System.out.println("let's do something");
                
            }else
                findSymbol = false;
            System.out.println("Nope");

            }
        }

}

Answer 1

Python 3.10 has a match statement which is the pythonic version of a switch . Anyhow as you said you can get the same result with if ... elif ... else :

if s=='+':
    ##handle addition
elif s=='-':
    ##handle subtraction
elif s=='*':
    ##handle multiplication
##etc
else:
    ##did not match any previous check, raise exception or something