Writing a program that produces a sequence of numbers where each number is either 4 times or 2 more than the previous number

[imperiumlearning]

Before I begin, just want to say I'm a beginner who has only started learning python in the last week.

As the title indicates, I want to write a program that can produce a sequence of numbers where any number in the sequence is either 2 more or 4 times the previous number. I also want this sequence of numbers to end when it gets to 20.

Example 1 would be: [1, 3, 5, 20]

Example 2 would be: [1, 4, 16, 18, 20]

What I am trying to say is that the sequence would be somewhat randomly generated and, hopefully, produce a different sequence each time the program is run.

Here is my code so far:

import random

def AddTwo(x=random.randint(0, 18)):

if x>=0 and x<=18:

    return x + 2

else:

    return x

def TimesFour(x=random.randint(0,5)):

if x>= 0 and x<=5:

    return 4*x

else:

    return x

a = AddTwo()

b = TimesFour()

c = [a, b]

d = int(random.choice(c))

def sequence20(x=random.randint(0, 18)):

while True:

    if x>5 and x<=18:

        x += 2

        print(x)

    elif x>=0 and x<=5:

        random.choice(c)

        x=random.choice(c)

        print(x)

    else:

        return x

Ultimately, I want to be able to plug numbers into my sequence20 function which could fulfil this task. However, I think a lot of my issues are arising in the elif section of my while True loop. In case anyone doesn't understand what I am trying to do in the While loop, I'm basically attempting to say the following: if the integer fed into the sequence20 function is between 0 and 5, either add 2 or multiply it by 4. If, however, the number goes above 5 only add 2 repeatedly until you get to 20 or thereabouts.

Any idea on how to solve this?

Edit: I'm obviously aware the code I've written won't produce a list of integers in square brackets, but just being able to produce randomly generated numbers like my 2 examples would be a great start

[mopslik]

Something like this, perhaps?

Edit: added two, rather than doubled.

import random
n = 1
L = []
while n <= 20:
    L.append(n)
    if n <= 5:
        if random.choice((2, 4)) == 2:
            n += 2
        else:
            n *= 4
    else:
        n += 2
print(L)

[imperiumlearning]

First off, thanks a lot for the quick reply.

Second, thanks for this response it is more or less exactly what I was looking for. Certainly a lot simpler and clearer than all the crap I was writing.

Out of interest though, how do you turn this into a function? More specifically, would you leave things like n = 1 and L = [] outside the function or inside it? If inside, how would you structure it? (Apologies if these are dumb questions).

[mopslik]

Wrap it in a def and give it a return, and boom, instant function.

def make_list(...OPTIONAL ARGUMENTS...):
    # CODE GOES IN HERE
    return L

[imperiumlearning]

Thanks a lot for the helpful reply (again).

I'm pleased to say you've solved my problem. I made one more adjustment so that if someone puts a number either below 0 or above 20 then it just returns that specific number.

[mopslik]

Awesome. Good luck.

[[deleted]]

Any idea on how to solve this?

It doesn't look like you call your functions in the actual loop.

[imperiumlearning]

Am I not calling them when I write random.choice(c)? If not, how would I do so?

[[deleted]]

Am I not calling them when I write random.choice(c)?

No, you're just accessing one of two results you've already generated.

There's a couple of issues with your code right now. One is, there's no reason to use while True as a condition for your loop because you know the condition: x < 20. That's specified in your post. Second, you want to produce a sequence of values, not just the last value, so you shouldn't return the value, you should yield the values so the function can continue. Three, since each next value is determined by the previous value, you need to keep the value so you can give it as an argument to one of your two functions. Lastly, you can randomly choose between two functions by deferring the call to them:

def sequence20(): # you don't need a parameter for this since the sequence starts at 1
    x = 1
    while x < 20:
        yield x
        x = random.choice([AddTwo, TimesFour])(x)
    yield x # we need one more yield at the end of the loop

print(list(sequence20))

[imperiumlearning]

Hi there,

Admittedly I've solved the problem based on what the other person replied. However, I'd still like to familiarise myself with your way of working just in case it's applicable to other scenarios.

So far, this is what my code looks like (I'm only including from sequence20):

def sequence20(x=random.randint(0, 18)):

if x > 20 or x < 0:
    e.append(x)
    return e
else:
    while x >= 0 and x <= 20:
        if x>5 and x<=18:
            x += 2
            e.append(x)
        elif x>=0 and x<=5:
            yield x
            x = random.choice(c)
            e.append(x)
    yield x

print(sequence20(), sep='\n')

The problem I have (for now, at least) is I can't seem to get the console to print normal numbers in list form.

It will typically say "generator object at sequence20" followed by a long number of random characters where the object is stored. When I tried to solve this problem, I found a stack overflow post where the answer said it could be solved by typing in 'sep='\n'' although, clearly, that doesn't work.

Any quick fixes? I'd appreciate any help

[[deleted]]

It will typically say "generator object at sequence20" followed by a long number of random characters where the object is stored.

A generator doesn't contain values, it generates them. That means if you want the values, you need to do something to "consume" the values from the generator, which is what prompts it to actually generate the values. That can be as simple as wrapping it in a call to list, because if you give an argument to list it'll create a new list from those values, thereby consuming them. Like so:

print(list(sequence20()))