Commenting print() breaks the Python code-CodePudding

I was faced with a very strange problem. With print() this code works.

def max_pairwise_product(numbers):
    max_1 = max(numbers)
    numbers.remove(max_1)
    max_2 = max(numbers)
    return max_1 * max_2


if __name__ == '__main__':
    input_n = int(input())
    print()              # <- comment of this line breaks the code
    input_numbers = [int(x) for x in input().split()]
    print(max_pairwise_product(input_numbers))

If I comment or delete the 10-th line with print() I got an error:

Traceback (most recent call last):
  File "C:\Users\...\maximum_pairwise_product_fast.py", line 12, in <module>
    print(max_pairwise_product(input_numbers))
  File "C:\Users\...\maximum_pairwise_product_fast.py", line 2, in max_pairwise_product
    max_1 = max(numbers)
ValueError: max() arg is an empty sequence*

Process finished with exit code 1

I use Python 3.9. PyCharm. I tried to launch with different virtual environments with Python 3.8 and 3.10 – the same error. When I launch in Jupyter and Colab – it is fane – no error.

There are no issues with any other Python script. I used the installation for several months and there was nothing strange.

It is so strange that I have no idea. Could you please help me?

CodePudding user response：

Try checking if your python interpreter is working correctly and is the latest python It might fix it or there's probably a problem with your ide.

CodePudding user response：

Back in 2018 or so, I found a similar strange issue in a Python program I downloaded that solved Rubik's cubes. Basically, the program ran just fine under Linux, but under Windows it was erroring out at a certain line that looked fine.

I ran "pyflakes" on that program, but pyflakes reported that nothing was wrong. Odd.

The line that supposedly contained the error was a list comprehension, much like your line here:

input_numbers = [int(x) for x in input().split()]

I replaced the list comprehension with a normal for-loop, and then the code ran fine with no errors. Basically, if I were to rewrite your line, I would replace it with the following three lines:

input_numbers = []
for x in input().split():
    input_numbers.append(int(x))

I have no idea why the error was happening in the first place, and only on Windows. (The version of Python3 I was using certainly supported list comprehensions; I checked.) But once I replaced the list comprehensions with a for-loop, the code worked.

So my advice is to replace your list-comprehension with a for-loop and see if that solves anything.

I don't know if that will work, but it's worth a shot.

P.S. I'm curious: Which operating system(s) does the error happen on?

P.P.S. I recommend adding input text to your input() calls (such as input("Type some space-separated numbers: "), even if just for posting here. Otherwise, when stackoverflow users run your code, it looks like your code is hanging.

CodePudding user response：

Thank you all for helping to refer me in the right direction. The reason for the error was a bug in PyCharm. It sent not was typed. The issue disappeared after the PyCharm update from version 2022.1.1 to 2022.1.2.