for loop in c++ and python

Question

I am very new to python.I had a small query about for loop in c++ and python.In c,c++ if we modify the variable i as shown in below example ,that new value of i reflects in the next iteration but this is not the case in for loop in python.So ,how to deal with it in python when it is really required to skip some iterations without actually using functions like continue ,etc.

for loop in c++

for(int i=0;i<5;++i)
{   
   if(i==2)
    i=i+2;

   cout<<i<<endl;
}

Output

for loop in python

for i in range(5):
     if i==2:
        i=i+2
     print i

Output

In Python, use while to do such things.

Daniel Fischer
– Daniel Fischer

2013-02-01 21:30:39 +00:00
Commented Feb 1, 2013 at 21:30 — Daniel Fischer
– Daniel Fischer, Commented Feb 1, 2013 at 21:30

OnePie · Accepted Answer · 2013-02-01 21:36:45Z

6

I'd in general advice against modifying the iteration variable in C++, as it makes the code hard to follow.

In python, if you know beforehand which values you want to iterate through (and there is not too many of them!) you can just build a list of those.

for i in [0,1,4]:
    print i

Of course, if you really must change the iteration variable in Python you can just use a while loop instead.

i = 0
while i < 5:
    if i==2:
        i=i+2
    print i
    i = i + 1

answered Feb 1, 2013 at 21:36

OnePie

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Comments

user334856 · Accepted Answer · 2013-02-01 21:31:12Z

4

This is because in python, at each iteration of the loop, the variable i is chosen as the next element in range(5). But, in c++, the variable i is managed by both the loop increment, and the stuff that happens inside the loop.

answered Feb 1, 2013 at 21:31

user334856

Comments

isedev · Accepted Answer · 2013-02-01 21:31:21Z

1

The i variable is being set at every iteration of the loop to the output of the range(5) iterator. Although you can modify in the loop, it gets overwritten.

answered Feb 1, 2013 at 21:31

isedev

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Comments

Corbin · Accepted Answer · 2013-02-01 21:31:22Z

1

i is reset each iteration, meaning any mutation to i is ignored the next loop around. As Daniel Fischer said in a comment, if you want to do this in Python, use a while loop.

It's like:

for (int i = 0; i < 5; ++i) {
    int x = i;
    if (x == 2) {
        x = x + 2;
    }
    std::cout << x << std::endl;
}

answered Feb 1, 2013 at 21:31

Corbin

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Comments

gefei · Accepted Answer · 2013-02-01 21:31:16Z

0

this is because range(5) is [0,1,2,3,4], for i in range(5) is therefore for i in [0,1,2,3,4]

answered Feb 1, 2013 at 21:31

gefei

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