c-style of assigning variable in the if-statement for python

Question

in c/c++, I can "assign a value to a variable" in if-statement as follows:

   int a;

   if ( (a = foo()) > 0)
   {
      printf("%d\n", a);
   }

Is there any equivalent statement for python?

Answer 1

Not really. In Python, an assignment is a statement, whereas in C it is an expression. The condition in the if statement must be an expression in both languages.

Answer 2

In Python the assignment in the if condition is forbidden so you end up with a syntax error, this design decision was done to protect against error like this:

in C you can easily do:

if (a = 1) {
  ...
}

while you mean:

if (a == 1) {
 ...
}

Answer 3

Until today, I believe the answer was no.

I thought that to be unfortunate, so I wrote a little Python module, which I call let , which allows you to do this kind of thing.

Install it like this:

pip install let

I believe the following will accomplish what you're looking for:

from let import let

if let(a = foo()):
    print(a)

I dropped the > 0 from your answer, making the assumption that foo will either return 0 or a positive integer. If I'm incorrect and you really do want to check if the return value is greater than 0, then this works too:

if let(a = foo()) > 0:
    print(a)

let also couples well with while loops, if you have a function which returns something different each time until eventually it returns something False . IE, IBM's DB2 module requires you to repeatedly call a fetch method to get each row from the database. You could use let to simplify the logic of looping over everything in it like this:

while let(result = db.fetch_results()):
    # do whatever with result here

Answer 4

No you can't do this and a good job too. This style of coding leads to complex and hard to read code.