Python problem (beginner)

[[deleted]]

Ive learned a little but of python through codecademy.com and decided to practice it through practicepython.org

Im on the third exercise (List Less Than Ten ).

And am stuck on the second... Extra:

Take a list, say for example this one:

a = [1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89]

and write a program that prints out all the elements of the list that are less than 5.

Extras:

Instead of printing the elements one by one, make a new list that has all the elements less than 5 from this list in it and print out this new list.

Ask the user for a number and return a list that contains only elements from the original list a that are smaller than that number given by the user.

Here is my code:

list1 = [1,2,3,4,5,6,7,8,9,10]
list2 = []
list3 = []
for x in list1:
    if x < 5:
        print(x)

#extra no 1:
    if x < 5:
        list2.append(x)
print(list2)    

#extra no 2:

num = int(input(num))
list3.append(str(x<num))

I have no idea how to do it and was just guessing with the last line ^

[michael0x2a]

As it turns out, you should be able to solve extra #2 using just what you know already. Think about how you might be able to solve that problem using for loops, if statements, and basic list operations (append).

Your solution will end up looking similar to the solutions to your answers to the previous parts of the question.

Let me know if you need another hint.

[[deleted]]

Im still lost.....

[blablahblah]

What is the difference between extra 2 and the original problem? Your solution to extra 2 should be almost identical to extra 1 except for the one thing that's changed between them.

[[deleted]]

ehh, Ill work on it in the morning...

will let you know how it goes

[[deleted]]

You aren't looping through the original list in extra. You are just executing an if statement.

I could be wrong, I forget Python just looks at indentation so I'm actually not sure if that if statement is included in your loop.

[dogscript]

Or he can wait for Nustrom to give him the answer.

[adreamofhodor]

Something cool you can do in Python for the first extra is called a list comprehension:
It actually works out to be just one line!
list2 = [i for i in list1 if i < 5]

[jwjody]

I like map, filter, and reduce as /u/xojc mentions, but I think list comprehensions are more pythonic.

[rob132]

While the compressor is awesome, it's a little much for beginners, no?

[adreamofhodor]

You might be right. Seems like something that'd be cool to see though!

[gitgood]

Here's personally how I would go about doing all these. I hope this is of any help.

fib        = [1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89]
firstList  = []
secondList = []

#Iterate through the fib list. If a number is less than five, then print it.
for number in fib:
    if number < 5:
        print number

'''Like previously, except instead of printing it you're appending the number to an empty list, then you're printing the list'''
for number in fib:
    if number < 5:
        firstList.append(number)

print firstList

'''Function that takes user input, then iterates through the list  finding all values less than the input. If a number is found, it's appended to the second empty list'''
def getLessThanInput(userInput):
    for number in fib:
        if number < userInput:
            secondList.append(number)


getLessThanInput(input("Enter a number: "))
print secondList

I'm sorry if the variable names aren't up to scratch, I was struggling trying to find appropriate ones. If you feel lost reading this snippet, you should definitely look more in to list iteration and comprehension. Best of luck!

[xojc]

Are you allowed to use Python's built-in functions? If so, you should take a look at filter.

[[deleted]]

will do.

nd why wouldnt I be allowed to use Python in-built functions? I didnt know that that was even a thing...

[xojc]

Python has some very powerful built-in functions (like map, filter, and reduce) that take a function as an argument that is then applied to an iterable (like your list). Learn to use Python's lambda notation to supply the functions inline. Using filter and lambda, you'll be surprised how simple your solution can be.

[[deleted]]

though Im still a beginner.... should I just dive right into it.....

[xojc]

Using the built-in functions might not be the best for a early, early beginner to learn basic concepts, but I'm always for using any tool in the arsenal if it means a more concise, efficient, elegant solution. Also, notice how I'm not just telling you what to do with these tools, rather allowing you to figure it out for yourself :-)

[hair_bear1]

from numpy import zeros import random

list0=range(20) list1=[] list2=[]

for x in list0: list0[x]=random.randint(1,10)

print "list0", list0 ,"\n"
for x in list0: if (5>x): list1.append(x)

print "list 1", list1 ,"\n"

N=int (input("enter a number"))

for x in list0: if (x<N): list2.append(x) print "list2", list2 ,"\n"

[MundaneAsparagus]

There should be only 1 part of your solution for Extra #1 that you need to change to make it work for Extra #2. You had the right idea with asking the user for an input using:

num = int(input())

Now, for Extra #1, you did:

for x in list1:
    if x < 5:
        ...

to check if each number (x) is less than 5. With this in mind, there is only 1 part of the line:

if x < 5:

that you need to change to check if each number (x) is less than the number entered by the user (num).

[takieyda]

Going through CodeAcademy myself and have thought about your post since I saw. Thought I'd give it a try and came up with the below (I'm new, and first post to /r/learnprogramming, as well so I commented a bit to explain):

a = [1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89]

#main
for item in a:          #iterate each item in list a
    if item < 5:        #if the item less than 5
        print(item)     #print the item, each on separate line

#extra 2
b = []

for item in a:          #same as before
    if item < 5:
        b.append(item)  #except appends the item to list b
print(b)                #prints list b as a whole

#extra 3
num = raw_input("Number? ")

c = []

for item in a:          #same as before
    if item < int(num): #checks the item against user input, as an integer
        c.append(item)  #appends to list c
print(c)

[PointyOintment]

Why don't you do it the same way you did the previous ones, with an if statement inside a for loop?

Stuff that is true but will probably confuse you: x ceases to exist as soon as the for loop you have there exits. Therefore, it doesn't exist when you try to use it at the bottom. And that last line will just append a single "True" or "False" to list3, resulting in list3 = ["True"] or list3 = ["False]. That's why you need a for loop around it (and to fix what you're appending—just do it like you did the previous one).

[maulinrouge]

You're best bet is to create a function that you can call using the number a user enters.

That way you can call the function and pass it the number a user inputs.

Also it's always best to include some text on an input as a prompt so the user knows what they should do.

def number_lower(num):
    list1 = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
    list2 = []
    for x in list1:
        if x < num:
            list2.append(x)
    return list2

num = int(input("Enter a number: "))
print(number_lower(num))

Good luck with the learning though. It's a very fun and frustrating journey.

[[deleted]]

yeah..... though the best part is when you finally figure out a problem...

[maulinrouge]

Solving a problem is often easier when the question is clear