translating C++ for loop to python

Question

I'm having a little trouble translating C++ to python. The trouble I have is with the boolean statements in the for loop for (Nbound = 1; Nbound < (Nobs + 1) && B < Beta; Nbound++) and for (Ndm = 0;(Ndm < (i + 1) && P3 > (0)) || PP == 0; Ndm++). I'm unsure how this would work in python, I don't think python allows boolean statements in a for loop, so I think I would have to call it inside with an IF statement, but I'm not entirely sure. Thanks for your help!

also, I've noticed a lot of empty variables in this code for example, float PP is there a way of doing this in python or would I just assign it a value of 0 then change it later?

    float Pf = 0; //The complement of Beta
    float B = 0; //Beta
    float P3;
    float PP;
    float Nbound = 1;
    for (Nbound = 1; Nbound < (Nobs + 1) && B < Beta; Nbound++) {
        int Ndm = 0;
        int Nbgd = Nobs; //Setting Ndm=Nobs
        Pf = 0; //Zeroing the placeholder for the sum
        float exp; //A variable to store the exponential
        for (int i = 0; i < (Nobs + 1); i++) //Summing over Nbgd+Ndm<NObs
        {
            P3 = 1;
            PP = 0;
            if (P1[Nbgd] > 0) {

                for (Ndm = 0;(Ndm < (i + 1) && P3 > (0)) || PP == 0; Ndm++) {
                    //P3 = dist(Ndm, Nbound);
                    Pf = Pf + (P1[Nbgd] * P3); //Summing over the probability
                    PP = PP + P3;
                }

            }

        }
    }
}

python does have while loops and any for loop can be transformed to an equivalent while loop — 463035818_is_not_an_ai
– 463035818_is_not_an_ai, Commented Jun 14, 2021 at 14:55
you could use for Nbound in range(1, Nobs + 1): if B >= Beta: break — furas
– furas, Commented Jun 14, 2021 at 15:23
Aside: none of B, Beta, P3 nor PP influence the loop conditions here, so it can be for Nbound in range(1, Nobs + 1): for i in range(0, Nobs + 1): for Ndm in range(0, i + 1): — Caleth
– Caleth, Commented Jun 14, 2021 at 15:52

Niko B · Accepted Answer · 2021-06-14 15:29:56Z

5

For loops in Python are meant for iteration over objects. If you want a loop with specific exit condition then you should use the while loop.

for loops in C can be described as :

for {initialization_statement; condition_expression; update_statement)
{
    body_statement_1;
    body_statement_2;
    ...
    body_statement_n;
}

The corresponding loop in Python is :

initialization_statement
while condition_expression:
   body_statement_1
   body_statement_2
   ...
   body_statement_n
   update_statement

answered Jun 14, 2021 at 15:29

Niko B

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2 Comments

Caleth Over a year ago

Aside: The C++ standard defines a for loop in terms of a while loop (with a slightly special handling of continue)

Niko B Over a year ago

Thanks Caleth. Interesting point I did not know.

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