=+ Python operator is syntactically correct

Question

I accidentally wrote:

total_acc =+ accuracy

instead of:

total_acc += accuracy

I searched the net and could not find anything. So what happened, why does Python think I mean what I am typing?

_{Computers trust us too much. :)}

Answer 1

If you are interested in catching this type of errors early, you can do that with static code analysis. For example, flake8:

$ cat test.py
total_acc = 0
accuracy = 10

total_acc =+ accuracy
$ flake8 test.py
test.py:4:12: E225 missing whitespace around operator

In this case, it is complaining about the extra space after the +, thinking that you actually meant total_acc = +accuracy. This would have helped you to discover the problem earlier.

FYI, pylint would catch that too.

Answer 2

This is the same as if you were to do like total_acc = -accuracy, except positive instead of negative. It basically is the same as total_acc = accuracy though, as adding a + before a value does not change it.

This is called an unary operator as there is only one argument (ex: +a) instead of two (ex: a+b).

This link explains it a little more.