我想排除所有不能被 7 整除且不是 (0,300) 范围内的 5 倍数的数字

Question

basically I have to get a list of numbers that are divisible by 7 but not multiples of 5. but for some reason when i put the conditions it tells me i have error.

for i in [x for x in xrange(0,100) if x%7 ==0 and if x%5 !=0 ]:
    print i

Answer 1

I know you posted something along the lines of a list comprehension but it's a bit hard to read. So a few things...

1. I would try writing this as a multi-line for loop before condensing it down to a list comprehension.
2. I'm not sure why you have an 'x' in here, and 'xrange' doesn't make sense. Edit: Just realized why I don't recognize xrange and it's because I never worked with Python 2.x

So thinking through this, you are basically looking for any number from 0-300 that is divisible by 7 but is not a multiple of 5.

Means we have a few things...

• range(0,301): Since range is not inclusive of our last value we want n+1
• Our number, let's say "i" is both... "i%7==0" and "i%5!=0"

So let's look line-by-line

for i in range(0,301):

Okay cool, now you don't need a nested for loop list comprehension like you did in your example. Now, you need to know "if" i is ____... So we need an if statement.

if i%7==0 and i%5!=0:

See the logic? And of course that if statement is inside of our for loop to loop over all the values in our range.

Finally, if our "i" meets our criteria, then we can print all the values.

print(i)

So, our final code looks like...

for i in range(0,301):
    if (i % 7 == 0) and (i % 5 != 0):
        print(i)

Of course, there are ways you can make this more elegant, but this is the general idea.

List Comprehension:

party = [i for i in range(0,301) if i%7==0 and i%5!=0]
print(party)

That stores them all in a list so you can access them whenever. Or you can print it without assigning it of course.

Edit: The title and then what you say in the body are kind of conflicting. After reading over my own answer, I'm not completely sure if that's what you're looking for, but that is how it came across to me. Hope it helps!

Answer 2

Your list comprehension is incorrect. It should be something similar to:

[x for x in xrange(100) if x%5 and not x%7]

Even better (more efficient) will be something similar to

[x for x in xrange (7, 100, 7) if x%5]

Even better will be ... Nah, we'll just stop here for now.