C++ for loop nested statements to python

up vote
2
down vote

favorite

How would I translate the following C++ for loop into a python for loop?

for(i = xSize - 1; i >= 0 && ptr.points[i] > temp; i--){

    doSomething;

}

I am having trouble because of the and operator. Without it, I know it would be like

for i in range(xSize - 1, 0, -1)

Is this equivalent?

for i in range(xSize - 1, 0, -1):

    if ptr.points[i] > temp:

        doSomething

asked Nov 19 at 20:35

paul

204

Just break out of the loop once the condition becomes false: for i in range(xSize-1, 0, -1): if i < 0 or ptr.points[i] <= temp: break else: doSomething
– pault
Nov 19 at 20:38

thanks, but why use the negation? Does it has advantages?
– paul
Nov 19 at 20:49

They should be equivalent. See the answer I posted (without the negation) for more explanation.
– pault
Nov 19 at 20:53

add a comment |

up vote
2
down vote

favorite

How would I translate the following C++ for loop into a python for loop?

for(i = xSize - 1; i >= 0 && ptr.points[i] > temp; i--){

    doSomething;

}

I am having trouble because of the and operator. Without it, I know it would be like

for i in range(xSize - 1, 0, -1)

Is this equivalent?

for i in range(xSize - 1, 0, -1):

    if ptr.points[i] > temp:

        doSomething

asked Nov 19 at 20:35

paul

204

Just break out of the loop once the condition becomes false: for i in range(xSize-1, 0, -1): if i < 0 or ptr.points[i] <= temp: break else: doSomething
– pault
Nov 19 at 20:38

thanks, but why use the negation? Does it has advantages?
– paul
Nov 19 at 20:49

They should be equivalent. See the answer I posted (without the negation) for more explanation.
– pault
Nov 19 at 20:53

add a comment |

up vote
2
down vote

favorite

How would I translate the following C++ for loop into a python for loop?

for(i = xSize - 1; i >= 0 && ptr.points[i] > temp; i--){

    doSomething;

}

I am having trouble because of the and operator. Without it, I know it would be like

for i in range(xSize - 1, 0, -1)

Is this equivalent?

for i in range(xSize - 1, 0, -1):

    if ptr.points[i] > temp:

        doSomething

asked Nov 19 at 20:35

paul

204

How would I translate the following C++ for loop into a python for loop?

for(i = xSize - 1; i >= 0 && ptr.points[i] > temp; i--){

    doSomething;

}

I am having trouble because of the and operator. Without it, I know it would be like

for i in range(xSize - 1, 0, -1)

Is this equivalent?

for i in range(xSize - 1, 0, -1):

    if ptr.points[i] > temp:

        doSomething

python c++ for-loop

asked Nov 19 at 20:35

paul

204

asked Nov 19 at 20:35

paul

204

asked Nov 19 at 20:35

paul

204

asked Nov 19 at 20:35

paul

204

asked Nov 19 at 20:35

paul

204

Just break out of the loop once the condition becomes false: for i in range(xSize-1, 0, -1): if i < 0 or ptr.points[i] <= temp: break else: doSomething
– pault
Nov 19 at 20:38

thanks, but why use the negation? Does it has advantages?
– paul
Nov 19 at 20:49

They should be equivalent. See the answer I posted (without the negation) for more explanation.
– pault
Nov 19 at 20:53

add a comment |

Just break out of the loop once the condition becomes false: for i in range(xSize-1, 0, -1): if i < 0 or ptr.points[i] <= temp: break else: doSomething
– pault
Nov 19 at 20:38

thanks, but why use the negation? Does it has advantages?
– paul
Nov 19 at 20:49

They should be equivalent. See the answer I posted (without the negation) for more explanation.
– pault
Nov 19 at 20:53

Just break out of the loop once the condition becomes false: for i in range(xSize-1, 0, -1): if i < 0 or ptr.points[i] <= temp: break else: doSomething
– pault
Nov 19 at 20:38

thanks, but why use the negation? Does it has advantages?
– paul
Nov 19 at 20:49

They should be equivalent. See the answer I posted (without the negation) for more explanation.
– pault
Nov 19 at 20:53

add a comment |

3 Answers
3

active

oldest

votes

up vote
0
down vote

Python itself has no support for this kind of operation.

However, your intuition is right. You can write as you stated, but as @François Andrieux correctly stated, you should also provide a break clause.

Also, you should take a look at itertools module provided by standard library. It offers a wide rage of functions to deal with efficient looping.

from itertools import takewhile, count 

for i in takewhile(lambda i:i > 0 and i<xSize -1 and ptr.Points[i] > temp, i = i-1): doSth()

edited Nov 19 at 20:58

answered Nov 19 at 20:38

bogdan tudose

867

1

I'm not an expert in Python, but it looks to me like the python version of the loop will iterate over all of the range and simply skip those that agree with the predicate. The c++ loop ends when the first such value is found, so even if future values don't match it, they will also be "skipped".
– François Andrieux
Nov 19 at 20:42

Thanks for the reply.
– paul
Nov 19 at 20:51

Yes, that's correct. Thank you for the completation, I also completed the answer including your observation
– bogdan tudose
Nov 19 at 20:57

add a comment |

up vote
0
down vote

The flow of a C++ for loop is roughly:

for ( initialize; condition; increment/decrement ) {

   doSomething;

}

Once the condition evaluates to false, execution will break out of the loop. In your example, the condition is i >= 0 && ptr.points[i] > temp which means that you will break out of the loop if the value of i goes negative or ptr.points[i] <= temp.

Thus you can equivalently write:

for(int i = xSize - 1; i >= 0; i--){

    if(ptr.points[i] > temp) {

        doSomething;

    }

    else {

        break;

    }

}

Which, translates quite easily to python as:

for i in range(xSize-1, 0, -1): 

    if i >= 0 and ptr.points[i] > temp: 

        doSomething

    else:

        break

(Though you don't really need the i >= 0 check)

edited Nov 19 at 21:04

answered Nov 19 at 20:52

pault

13.7k31744

Thanks for the reply. In the python if statement you used or, I believe that is a typo right?
– paul
Nov 19 at 21:00

@paul indeed it was a typo. fixed it. Also note that this is different than what you posted in your question, because your version will not break out of the loop.
– pault
Nov 19 at 21:04

Yes. I understand that part.
– paul
Nov 19 at 21:22

add a comment |

up vote
0
down vote

I think this should be okay as a while loop and intuitive, too, IMHO

i=xSize-1

while True:

    if ptr.points[i] > temp:

        doSomething 

    else:

        break

    i-=1

answered Nov 19 at 21:08

Matt Cremeens

3,19632049

add a comment |

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3 Answers
3

active

oldest

votes

3 Answers
3

active

oldest

votes

up vote
0
down vote

Python itself has no support for this kind of operation.

However, your intuition is right. You can write as you stated, but as @François Andrieux correctly stated, you should also provide a break clause.

Also, you should take a look at itertools module provided by standard library. It offers a wide rage of functions to deal with efficient looping.

from itertools import takewhile, count 

for i in takewhile(lambda i:i > 0 and i<xSize -1 and ptr.Points[i] > temp, i = i-1): doSth()

edited Nov 19 at 20:58

answered Nov 19 at 20:38

bogdan tudose

867

1

I'm not an expert in Python, but it looks to me like the python version of the loop will iterate over all of the range and simply skip those that agree with the predicate. The c++ loop ends when the first such value is found, so even if future values don't match it, they will also be "skipped".
– François Andrieux
Nov 19 at 20:42

Thanks for the reply.
– paul
Nov 19 at 20:51

Yes, that's correct. Thank you for the completation, I also completed the answer including your observation
– bogdan tudose
Nov 19 at 20:57

add a comment |

up vote
0
down vote

Python itself has no support for this kind of operation.

However, your intuition is right. You can write as you stated, but as @François Andrieux correctly stated, you should also provide a break clause.

Also, you should take a look at itertools module provided by standard library. It offers a wide rage of functions to deal with efficient looping.

from itertools import takewhile, count 

for i in takewhile(lambda i:i > 0 and i<xSize -1 and ptr.Points[i] > temp, i = i-1): doSth()

edited Nov 19 at 20:58

answered Nov 19 at 20:38

bogdan tudose

867

1

I'm not an expert in Python, but it looks to me like the python version of the loop will iterate over all of the range and simply skip those that agree with the predicate. The c++ loop ends when the first such value is found, so even if future values don't match it, they will also be "skipped".
– François Andrieux
Nov 19 at 20:42

Thanks for the reply.
– paul
Nov 19 at 20:51

Yes, that's correct. Thank you for the completation, I also completed the answer including your observation
– bogdan tudose
Nov 19 at 20:57

add a comment |

up vote
0
down vote

Python itself has no support for this kind of operation.

However, your intuition is right. You can write as you stated, but as @François Andrieux correctly stated, you should also provide a break clause.

Also, you should take a look at itertools module provided by standard library. It offers a wide rage of functions to deal with efficient looping.

from itertools import takewhile, count 

for i in takewhile(lambda i:i > 0 and i<xSize -1 and ptr.Points[i] > temp, i = i-1): doSth()

edited Nov 19 at 20:58

answered Nov 19 at 20:38

bogdan tudose

867

Python itself has no support for this kind of operation.

However, your intuition is right. You can write as you stated, but as @François Andrieux correctly stated, you should also provide a break clause.

Also, you should take a look at itertools module provided by standard library. It offers a wide rage of functions to deal with efficient looping.

from itertools import takewhile, count 

for i in takewhile(lambda i:i > 0 and i<xSize -1 and ptr.Points[i] > temp, i = i-1): doSth()

edited Nov 19 at 20:58

answered Nov 19 at 20:38

bogdan tudose

867

edited Nov 19 at 20:58

answered Nov 19 at 20:38

bogdan tudose

867

answered Nov 19 at 20:38

bogdan tudose

867

answered Nov 19 at 20:38

bogdan tudose

867

1

I'm not an expert in Python, but it looks to me like the python version of the loop will iterate over all of the range and simply skip those that agree with the predicate. The c++ loop ends when the first such value is found, so even if future values don't match it, they will also be "skipped".
– François Andrieux
Nov 19 at 20:42

Thanks for the reply.
– paul
Nov 19 at 20:51

Yes, that's correct. Thank you for the completation, I also completed the answer including your observation
– bogdan tudose
Nov 19 at 20:57

add a comment |

1

I'm not an expert in Python, but it looks to me like the python version of the loop will iterate over all of the range and simply skip those that agree with the predicate. The c++ loop ends when the first such value is found, so even if future values don't match it, they will also be "skipped".
– François Andrieux
Nov 19 at 20:42

Thanks for the reply.
– paul
Nov 19 at 20:51

Yes, that's correct. Thank you for the completation, I also completed the answer including your observation
– bogdan tudose
Nov 19 at 20:57

I'm not an expert in Python, but it looks to me like the python version of the loop will iterate over all of the range and simply skip those that agree with the predicate. The c++ loop ends when the first such value is found, so even if future values don't match it, they will also be "skipped".
– François Andrieux
Nov 19 at 20:42

Thanks for the reply.
– paul
Nov 19 at 20:51

Yes, that's correct. Thank you for the completation, I also completed the answer including your observation
– bogdan tudose
Nov 19 at 20:57

add a comment |

up vote
0
down vote

The flow of a C++ for loop is roughly:

for ( initialize; condition; increment/decrement ) {

   doSomething;

}

Thus you can equivalently write:

for(int i = xSize - 1; i >= 0; i--){

    if(ptr.points[i] > temp) {

        doSomething;

    }

    else {

        break;

    }

}

Which, translates quite easily to python as:

for i in range(xSize-1, 0, -1): 

    if i >= 0 and ptr.points[i] > temp: 

        doSomething

    else:

        break

(Though you don't really need the i >= 0 check)

edited Nov 19 at 21:04

answered Nov 19 at 20:52

pault

13.7k31744

Thanks for the reply. In the python if statement you used or, I believe that is a typo right?
– paul
Nov 19 at 21:00

@paul indeed it was a typo. fixed it. Also note that this is different than what you posted in your question, because your version will not break out of the loop.
– pault
Nov 19 at 21:04

Yes. I understand that part.
– paul
Nov 19 at 21:22

add a comment |

up vote
0
down vote

The flow of a C++ for loop is roughly:

for ( initialize; condition; increment/decrement ) {

   doSomething;

}

Thus you can equivalently write:

for(int i = xSize - 1; i >= 0; i--){

    if(ptr.points[i] > temp) {

        doSomething;

    }

    else {

        break;

    }

}

Which, translates quite easily to python as:

for i in range(xSize-1, 0, -1): 

    if i >= 0 and ptr.points[i] > temp: 

        doSomething

    else:

        break

(Though you don't really need the i >= 0 check)

edited Nov 19 at 21:04

answered Nov 19 at 20:52

pault

13.7k31744

Thanks for the reply. In the python if statement you used or, I believe that is a typo right?
– paul
Nov 19 at 21:00

@paul indeed it was a typo. fixed it. Also note that this is different than what you posted in your question, because your version will not break out of the loop.
– pault
Nov 19 at 21:04

Yes. I understand that part.
– paul
Nov 19 at 21:22

add a comment |

up vote
0
down vote

The flow of a C++ for loop is roughly:

for ( initialize; condition; increment/decrement ) {

   doSomething;

}

Thus you can equivalently write:

for(int i = xSize - 1; i >= 0; i--){

    if(ptr.points[i] > temp) {

        doSomething;

    }

    else {

        break;

    }

}

Which, translates quite easily to python as:

for i in range(xSize-1, 0, -1): 

    if i >= 0 and ptr.points[i] > temp: 

        doSomething

    else:

        break

(Though you don't really need the i >= 0 check)

edited Nov 19 at 21:04

answered Nov 19 at 20:52

pault

13.7k31744

The flow of a C++ for loop is roughly:

for ( initialize; condition; increment/decrement ) {

   doSomething;

}

Thus you can equivalently write:

for(int i = xSize - 1; i >= 0; i--){

    if(ptr.points[i] > temp) {

        doSomething;

    }

    else {

        break;

    }

}

Which, translates quite easily to python as:

for i in range(xSize-1, 0, -1): 

    if i >= 0 and ptr.points[i] > temp: 

        doSomething

    else:

        break

(Though you don't really need the i >= 0 check)

edited Nov 19 at 21:04

answered Nov 19 at 20:52

pault

13.7k31744

edited Nov 19 at 21:04

answered Nov 19 at 20:52

pault

13.7k31744

answered Nov 19 at 20:52

pault

13.7k31744

answered Nov 19 at 20:52

pault

13.7k31744

Thanks for the reply. In the python if statement you used or, I believe that is a typo right?
– paul
Nov 19 at 21:00

@paul indeed it was a typo. fixed it. Also note that this is different than what you posted in your question, because your version will not break out of the loop.
– pault
Nov 19 at 21:04

Yes. I understand that part.
– paul
Nov 19 at 21:22

add a comment |

Thanks for the reply. In the python if statement you used or, I believe that is a typo right?
– paul
Nov 19 at 21:00

@paul indeed it was a typo. fixed it. Also note that this is different than what you posted in your question, because your version will not break out of the loop.
– pault
Nov 19 at 21:04

Yes. I understand that part.
– paul
Nov 19 at 21:22

Thanks for the reply. In the python if statement you used or, I believe that is a typo right?
– paul
Nov 19 at 21:00

@paul indeed it was a typo. fixed it. Also note that this is different than what you posted in your question, because your version will not break out of the loop.
– pault
Nov 19 at 21:04

Yes. I understand that part.
– paul
Nov 19 at 21:22

add a comment |

up vote
0
down vote

I think this should be okay as a while loop and intuitive, too, IMHO

i=xSize-1

while True:

    if ptr.points[i] > temp:

        doSomething 

    else:

        break

    i-=1

answered Nov 19 at 21:08

Matt Cremeens

3,19632049

add a comment |

up vote
0
down vote

I think this should be okay as a while loop and intuitive, too, IMHO

i=xSize-1

while True:

    if ptr.points[i] > temp:

        doSomething 

    else:

        break

    i-=1

answered Nov 19 at 21:08

Matt Cremeens

3,19632049

add a comment |

up vote
0
down vote

I think this should be okay as a while loop and intuitive, too, IMHO

i=xSize-1

while True:

    if ptr.points[i] > temp:

        doSomething 

    else:

        break

    i-=1

answered Nov 19 at 21:08

Matt Cremeens

3,19632049

I think this should be okay as a while loop and intuitive, too, IMHO

i=xSize-1

while True:

    if ptr.points[i] > temp:

        doSomething 

    else:

        break

    i-=1

answered Nov 19 at 21:08

Matt Cremeens

3,19632049

answered Nov 19 at 21:08

Matt Cremeens

3,19632049

answered Nov 19 at 21:08

Matt Cremeens

3,19632049

answered Nov 19 at 21:08

Matt Cremeens

3,19632049

add a comment |

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