Python For loops in While loop, starting for loop with a specific value

Question

I've started learning Python a few days ago and I ran into a program while coding something.

Here's what I want to do using C++ code

number = SOME_NUMBER;
while(1) {
    for(int i=number; i<sizeOfArray; i++) {
        // do something
    }
    number = 0;
}

Basically, for the very first iteration of my for loop, I want to start i at number. Then for every other time i go through the for loop, I want to start it at 0.

My kind of hacky idea that I can think of right now is to do something like:

number = SOME_NUMBER
for i in range(0, len(array)):
    if i != number:
        continue
    // do something

while True:
    for i in range(0, len(array)):
        // do something

Is this the best way or is there a better way?

Solution 1

what is the problem with this?

starting_num = SOME_NUMBER
while True:
    for i in xrange(starting_num, len(array)):
        # do code
    starting_num = 0

it does exactly what you want.

however, i think there are better ways to do things especially if the solution seems "hacky".

if you gave an idea of what you wanted to do, maybe there is a better way

Solution 2

I don't see why you couldn't just do the same thing you are in C:

number = SOME_NUMBER
while True:
    for i in range(number, len(array)):
        # do something
    number = 0

BTW, depending on which version of Python you're using, xrange may be preferable over range. In Python 2.x, range will produce an actual list of all the numbers. xrange will produce an iterator, and consumes far less memory when the range is large.

Solution 3

In Python, stepping over a collection in the traditional sense is not ideal. The ability to loop - to iterate - over an object is controlled by the object, so you don't need to manually step through counters as you would in the for loop in C++.

As I understand it, what you are trying to do here is execute the same piece of code over each item in a list (there are no arrays in Python), a multiple number of times.

To do that:

def whatever_function(foo):
   # some code here that works on each item on the list
   # foo is an item of the list

while True:
   map(whatever_function, some_list)