List index out of range even when I have bounded the value (python)-CodePudding

I have the following code and it works most of the time when I run it:


marvel_heroes = ['Wolverine','Spider-Man','Thor','Iron Man','Hulk','Captain America','Deadpool',
'Daredevil','Cyclops','Mr Fantastic','Professor X', 'Doctor Strange','Thing','Black Panther','Black Widow','Hawkeye','Vision','Shang-Chi', 'Ant-Man','Quicksilver','Star Lord',
'Rocket Raccoon','Drax','War Machine','Falcon']

marvel_heroes.append('Captain Marvel')
#print(marvel_heroes)

length = len(marvel_heroes)
print(length)
team = [marvel_heroes[random.randint(0, length)],marvel_heroes[random.randint(0, length)], marvel_heroes[random.randint(0, length)] ]


print('My team is:')
print(team)
print("\n")

Occasionally I get this error though:

Traceback (most recent call last):
  File "main.py", line 12, in <module>
    team = [marvel_heroes[random.randint(0, length)],marvel_heroes[random.randint(0, length)], marvel_heroes[random.randint(0, length)] ]
IndexError: list index out of range

I don't really understand how it can be out of range when I have bounded it by the length variable, is this some sort of memory overflow issue or maybe a problem with having duplicate values sometimes?

CodePudding user response：

The upper boundary of random.randint is inclusive, so you'd have to do

random.randint(0, length - 1)

That being said, I'd recommend you use

team  = random.sample(marvel_heroes, 3)

CodePudding user response：

The docs on randint() are clear:

Return a random integer N such that a <= N <= b. Alias for randrange(a, b 1).

Notice this includes the possibility that both a and b can be returned. So with a length of 5, randint can produce 5, which will be out of bounds for zero indexed lists.random.choices() or random.sample() might be better functions for this.

team = random.sample(marvel_heroes, 3)

choices() will replicate your current behavior, but sample() will give you a random unique selection which seem like what you want.

CodePudding user response：

According to the official documentation, randint(a,b) will return a value x so that a <= x <= b is true.

You could go for randrange() instead to get a <= x < b instead.