Question

[community edit: original title was “python conditionals”, OP is asking what is wrong with code below]

I made a function that’s supposed to determine if three sides can theoretically form a triangle. It works fine in my opinion , but when i input the code in pyschools.com website, it tells that in some test cases it doesn’t work (unfortunately it doesn’t show me the cases it didn’t work). Is something missing from my code, so in some special cases my logic breas down? Thank you very much for your help.
Here’s the function:

import math
def isTriangle(x, y, z):
    if x > 0 and y > 0 and z > 0:
        if x > y and x > z:
            c = x
        elif y > x and y > z:
            c = y
        else:
            c = z
        if c == math.sqrt(x**2 + y**2):
            return True
        else:
            return False
    else:
        return False

Answer 1

It is easier to just do:

def isTriangle(sides):
    smallest,medium,biggest = sorted(sides)
    return smallest+medium>=biggest and all(s>0 for s in sides)

(edit: I have decided to say that 2,2,4 is technically a triangle, but a degenerate triangle; change >= to > if you do not consider it to be a triangle.)

This is exactly what you’re doing. You are calculating c = largest = max(x,y,z) correctly, but then doing return math.sqrt(x**2+y**2) which checks if it is a right triangle.

Demo:

>>> isTriangle([2,2,6])
False
>>> isTriangle((5,5,9))
True
>>> isTriangle([-1,2,2])
False

Below I mention how your code can be simplified:

import math               # from math import * for such common functions
def isTriangle(x, y, z):  # better to pass in a tuple or object, but this works
    if x>0 and y>0 and z>0:  # (then you could do all(s>0 for s in sides))
                             # (you could also do isTriangle(*sides))
                             # (you might need to add checks len(sides)==3
                             #  if your input data might include e.g. squares)
        if x > y and x > z:    # \
            c = x              #  |
        elif y > x and y > z:  #  > This is the same as c = max(x,y,z)
            c = y              #  |
        else:                  #  |
            c = z              # /
        if c == math.sqrt(x**2 + y**2): # \
            return True                 #  | Same as return c==sqrt(x**2+y**2)
        else:                           #  |  
            return False                # /   
    else:
        return False

“if bool return True else return False” is the SAME as “return bool” in any almost any modern programming language. The former is unnecessarily verbose and should never be used.