[Tutor] Program to find if a number entered by user is a prime number or not

[Alan Gauld]

On 16/10/2020 02:30, Manprit Singh wrote:

> x = int(input("Enter any positive number"))
> a = "not prime"
> if all(x%i for i in range(2, int(x**0.5) + 1)):
>     if x < 2:
>         pass
>     else:
>         a = "prime"
> else:
>     pass
> print(x,"is",a)

This is bad on several counts.
The biggest issue is that you do the call to all() before checking if
the no is <2 which is a huge wasted effort.
Much better to put the check for <2 before calling all()

Also pass does nothing so there is no need to have
else: pass
just leave off the else.

And if you have pass in an if and code in the else that means you should
probably invert the if condition.


> Just need to know if my way of implementing the problem is correct ? Can
> this program be further optimised ?

Its very convoluted. I notice you have now pasted two better solutions.
I'll comment on them separately.


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Alan G
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