C to Python : For loop

Question

So I have this code in C which outputs the following :

Code :

scanf("%ld",&N);
long long A[N];
for(i=1;i<=N;i++)
    scanf("%lld", &A[i]);
for(i=1;i<N;i++)
    for(j=i;j<=N-1;j++) {
        printf("%d %d\n", A[i], A[j+1]);

Input :

5
1 2 3 4 5

Output :

How do I get the same output using python 3.7.x ?

Tried :

A = [1,2,3,4,5]
for i in range(len(A)):
        for j in range(len(A)):
            try:
                print(A[i],A[j+1])
            except IndexError:
                pass

Tried Output :

This is the output that I am getting which is just traversing each loop, printing the value out and so getting the repeated pairs.

Help appreciated, thank you !

In C, an array declared as A[N] has N entries, A[0] through A[N-1]. Accessing A[N] invokes undefined behaviour, which is going to be hard to replicate exactly in Python... — Ture Pålsson
– Ture Pålsson, Commented Dec 13, 2019 at 7:59
print(*(f'{j} {k}' for i, j in enumerate(a) for k in a[i + 1:]), sep='\n') cough — deceze
– deceze ♦, Commented Dec 13, 2019 at 8:05

CristiFati · Accepted Answer · 2019-12-13 08:16:49Z

3

That's not the way of doing it:

try / except blocks are costly, and there's actually no need for them here
That form of for isn't very Pythonic

You should try to replicate as close as possible the C loop. For that, [Python 3. Docs]: Built-in Functions - enumerate(iterable, start=0) comes in handy (allows working on element indexes). Also, sequence slicing was used.

>>> a = [1, 2, 3, 4, 5]
>>>
>>> for idx0, elem0 in enumerate(a):
...     for elem1 in a[idx0 + 1:]:
...         print(f"{elem0} {elem1}")
...
1 2
1 3
1 4
1 5
2 3
2 4
2 5
3 4
3 5
4 5

edited Dec 13, 2019 at 8:16

answered Dec 13, 2019 at 7:56

CristiFati

41.6k9 gold badges68 silver badges115 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Alexander Over a year ago

This solution is much more pythonic (although your indentationis off on your print statement).

CristiFati Over a year ago

Thx, @Alexander, apparently I overlooked several issues because I was in a rush.

David · Accepted Answer · 2019-12-13 08:03:22Z

2

you can use the same logic you did with the c code, meaning that j will start from i:

A = [1,2,3,4,5]
for i in range(len(A)):
        for j in range(i, len(A)):
            try:
                print(A[i],A[j+1])
            except IndexError:
                pass

another elegant solution is using itertools module:

from itertools import combinations

A = [1,2,3,4,5]
comb = combinations(A, 2)
for c in comb:
    print(c)

edited Dec 13, 2019 at 8:03

answered Dec 13, 2019 at 7:53

David

8,3782 gold badges21 silver badges40 bronze badges

Collectives™ on Stack Overflow

C to Python : For loop

2 Answers 2

2 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related