Python list comprehension with conditional and double for loop syntax error

Question

I am trying to count the number of times the elements in my list 'predicted' equal the corresponding elements in my list 'actual' when said 'actual' elements equal 1 (the number of 'true positives').

Here's my code:

def F_approx(predicted, actual):
   est_tp = np.sum([int(p == a) if a for p in predicted for a in actual])
   est_fn = np.sum([int(p !=a) if a for p in predicted for a in actual])
   est_recall = est_tp / (est_tp + est_fn)
   pr_pred_1 = np.sum([int(p == 1) for p in predicted]) / len(predicted)
   est_f = np.power(est_recall, 2) / pr_pred_1
   return(est_f)

Which looks correct to my eye, but I get an error:

    File "<ipython-input-17-3e11431566d6>", line 2
       est_tp = np.sum([int(p == a) if a for p in predicted for a in actual])
                                           ^ 
    SyntaxError: invalid syntax

Thanks for the help.

Answer 1

The if goes after the looping expression:

[int(p == a) for p in predicted for a in actual if a]

---

However, it really looks like you want to zip these together:

[int(p == a) for p, a in zip(predicted, actual)]

Answer 2

the if is placed at the end of the list comprehension

[int(p == a) for p in predicted for a in actual if a]

as a side note, with your particular construct you can add a ternary operation and have an else in your list comprehension

[int(p == a) if a else '' for p in predicted for a in actual if a]

adding else to the end of the list comprehension will throw a SyntaxError