Python Hanging on Length and Split functions

Question

I have a bit of code and it is hanging when I run it. I have narrowed it down to the following line. When I remove this line, my code does not hang.

However, there is nothing in this line which would make me think it could hang. There is no loops. Is there any known issues where string functions can hang given unknown input?

Here is the line causing the problem:

len(body.split("
")[-1]) >= 67

Here is the full function. Notice I have commented things out trying to narrow this down:

    def __str__(self):
        body = ""
        for i in range(0, self.height):
            for j in range (0, self.width):
                body += str(clamp(self.canvas[j][i]).red)
                if len(body.split("
")[-1]) >= 67 and j != self.width - 1:
                    body += "
"
                else:
                    body += " "
                #body += str(clamp(self.canvas[j][i]).green)
                #if len(body.split("
")[-1]) >= 67 and j != self.width - 1:
                #    body += "
"
                #else:
                #    body += " "
                #body += str(clamp(self.canvas[j][i]).blue)
                #if len(body.split("
")[-1]) >= 67 and j != self.width - 1:
                #    body += "
"
                #elif j != self.width - 1:
                #    body += " "
            if i != self.height - 1:
                body += "
"
        return body

question from:https://stackoverflow.com/questions/65643580/python-hanging-on-length-and-split-functions

Answer 1

After adding some print statements printing i and j in the for loop, I found that it was running, but slowing down at an almost exponential speed as i increased. Because of this continued exponential slow down, it seemed as if it will never finish.

I rewrote the str function and sped up the total time to write_file() to 12 seconds for a canvas of size 900 by 550.

Here is the new speedier function:

    def __str__(self):
        body = ""
        for i in range(0, self.height):
            cur = ""
            for j in range (0, self.width):
                clamped = clamp(self.canvas[j][i])
                print(str(i) + " " + str(j))
                cur += str(clamped.red)
                if len(cur) >= 67 and j != self.width - 1:
                    cur += "
"
                    body += cur
                    cur = ""
                else:
                    cur += " "
                cur += str(clamped.green)
                if len(cur) >= 67 and j != self.width - 1:
                    cur += "
"
                    body += cur
                    cur = ""
                else:
                    cur += " "
                cur += str(clamped.blue)
                if len(cur) >= 67 and j != self.width - 1:
                    cur += "
"
                    body += cur
                    cur = ""
                elif j != self.width - 1:
                    cur += " "
            body += cur
            if i != self.height - 1:
                body += "
"
        return body