missing a step.

Question

Yesterday I tried to solve this problem
Given a range of numbers. Iterate from first number to the end number and print the sum of the current number and previous number.
x =[x for x in range(0,20,2)]
for y in x:
if y == 0:
print(0)
else:
print(2*y-2)
It work but only if you know the interval between the number and if it is constant.
So I tried to find a way to check for calculating and checking the interval in a list

I used a for loop

for y in x:
d = x[y] - x[-1]

and an if/else to check that d was equal to the value on the first step.
It was working fine for a list without step (0,1,2,3,4), but not at all if there was any step. With a step of two only half the element of the list where compared.

Took me one hour to figure out that
x[y] was not the value of x for the element y, but the value of x at the indice y.
So in the case of an odd list : [0,2,4,6] for iteration I had
0
4 that is x[2]
and a message error because x[4] does not exist.

Finding the source of the error was a lot of fun, because I had to write many variation of my code to understand where was the issue.

I ended up understanding that I had to use enumarte and that was the final code.
x =[0,1,2,3,5,9,-5]
c = x[1] - x[0]
print(x)
print(f"First step is {c}")
for i,j in enumerate(x):
if i > 0:
d = x[i]-x[i-1]
else:
d =c
if d != c:
print(f"none regular step between {i-1} and {i}, the step is {d}")

Answer 1

Hello no real question because I solved this by myself.
But when I post people make suggestion on other way to solve the issue.
That's how I learn about enumerate.
I am a total newbie and I am learning with " a crash course in python" and by trying to do some exercise.

I will have a look at the zip function, never heard of this one before.

Answer 2

Great learning, although I don't really see a question here, you seem to have figured this out yourself. Well done ;)

I can show you an even more pythonic solution, its simplicity is just amazing and it also works with lists that are empty or have 1 element...
It used the zip() function, to combine the list with a sliced version of itself.

https://code.sololearn.com/cZgO80zEG4Y0/?ref=app

Answer 3

nicolas seespan, in your code you have an expression "c = x[1] - x[0]" that fills var c. But it's never used?

Answer 4

And the answer to the initial problem

x =[0,1,2,3,5,9,-5]
c = x[1] - x[0]
print(x)
for i,j in enumerate(x):
if i > 0:
y = x[i] + x[i-1]
print(y)
else:
y = x[0]
print(y)

This one will works not matter what the composition of the list :-).

Answer 5

Hello it was a part from the version of the code which was checking the interval
I forgot to remove it.