Print a range with selected numbers omitted

Question

I need to print those numbers in console:

0
1
2
3
-
5
6
7
8
-
10
11
12
13
-
15
16
17
18

As you can see I am not printing 4, 9, 14. So I coded this:

top = 18
counter = 0
print("Using option 1")
for i in range(top -2):
 print(counter)
 
 if counter == 3 or counter == 8 or counter == 13:
 counter = counter + 2
 
 else:
 counter = counter + 1
print("Using option 2")
i = -1
while i < top:
 if i == 3 or i == 8 or i == 13:
 i = i + 2
 print(i)
 else:
 i = i +1
 print(i)

The output of the above code is:

Using option 1
0
1
2
3
5
6
7
8
10
11
12
13
15
16
17
18
Using option 2
0
1
2
3
5
6
7
8
10
11
12
13
15
16
17
18

As you can see my code is working well. In option1 I used a for loop. And in option2 I used a while loop.

So I would like to know if there is a way to make some of that option more dynamic just by using the top value, or improve the algorithm.

• Reinderien: Are you printing the hyphens, or not? Your specification says yes, your code says no.

Answer 1

• Save your non-printed into single set exceptions = (4, 9, 14), that way you can test it nicely as index in exceptions or index not in exceptions for negative.
• Rather than trying to fiddle and increment your counter value yourself, just use range index and print only if you want it to print:

Example:

top = 20
exceptions = set((4, 9, 14,))
for index in range(top):
 if index not in exceptions:
 print(index)

If you were to go more in functional way (I recommend that), you can use filter function:

top = 20
exceptions = set((4, 9, 14,))
for index in filter(lambda i: i not in exceptions, range(top)):
 print(index)

Edit: Changed exceptions from tuple to set as suggested in a comment.

• Reinderien: Isn't the more functional way to join() on an iterable?
• K.H.: Now I understand what you meant :) I used filter, cause in my head, printing is usually something temporary to test, but then you in reality use the data in some other way.
• BruceWayne: Since OP is an admitted beginner, could you explain a little how lambda works here?
• David G.: The one other problem with both your original solutions and this solution is performance. For a tuple, index not in exceptions will be O(n) for n=len(exceptions). To do better, use: exceptions = set((4, 9, 14)). This actually won't matter much for 3 exceptions, but have 3000 and it will be critical.

Answer 2

You need to work harder at identifying the repeating patterns in your code. You're really printing uniformly-spaced groups with separators between them. Uniformly-spaced groups are better-represented with range() calls. The works can be formatted using two levels of join: the first within the group, and the second stringing the groups together.

In the following suggested code I've deliberately avoided writing a one-liner to make it easier to understand.

Suggested

spacing = 5
group_starts = range(0, 20, spacing)
separator = '-'
everything = f'\n{separator}\n'.join(
 '\n'.join(
 str(i) for i in range(start, start + spacing - 1)
 )
 for start in group_starts
)
print(everything)

Answer 3

How you display it is to your own taste but the core functionality is essentially a range with exceptions. Using hardcode to go through while loops and using lambda functions is all good but it seems overly complicated for a simple function. Perhaps use a reference and construct a list with comprehension. ie:

def start(ex_1, ex_2, ex_3):
 ref = [ex_1, ex_2, ex_3]
 num_list = [x for x in range(1, 19) if x not in ref]
 print(num_list)
start(4, 9, 14)

• Miguel Alorda: Downvote: This solution is not extensible: if a new exception was to be added, a new parameter would have to be added to the function, potentially making all other existing calls to it invalid. Also, as mentioned already in another answer, using a list/tuple makes its time complexity O(N). A set would provide a time complexity of O(1). Moreover, prefer immutability over mutability (tuple over list), as it is less error prone. Lastly, the range is not configurable, making it a non-reusable function
• Miguel Alorda: Also, core logic should be separated from presentation to allow reusability. That is, the print should not be done within the function
• Barb: The OP said he needs to print the numbers in the console. Not that he wants to run a pep8 format defined operation. To put simply, you dont know what you on about - his question is answered and this runs correctly and does exactly what he is asking to happen.
• Peilonrayz: @MiguelAlorda's comments are entirely correct. I am also one of the top Python reviewers on the site, so I'm confident I know what I'm on about.
• Peilonrayz: Please do not edit the question. You are unlikely to edit the question in a way which would be inline with our rules. Sure, we can agree to disagree. You've now got two downvotes and some comments why there are downvotes. Your disagreement with editing your answer means these downvotes and comments will be permanently attached to your answer. And everyone agrees the situation is fine.