Changing the number of iterations in a for loop

Question

I have code like this:

loopcount = 3 for i in range(1, loopcount)    somestring = '7'    newcount = int(somestring)    loopcount = newcount 

so what I want is to modify the range of the for 'inside' the loop.

I wrote this code expecting the range of the for loop would change to (1,7) during the first loop, but it didn't happen.

Instead, no matter what number I put in, it only runs 2 times. (I want 6 times.. in this case)

I checked the value using print like this:

    loopcount = 3     for i in range(1, loopcount)        print loopcount        somestring = '7'        newcount = int(somestring)        loopcount = newcount        print loopcount #output: 3 7 7 7 

What is wrong? the number has been changed.

Where is my thinking wrong?

Answer 1

The range is created based on the value of loopcount at the time it is called--anything that happens to loopcount afterwards is irrelevant. What you probably want is a while statement:

loopcount = 3 i = 1 while i < loopcount:     somestring = '7'     loopcount = int(somestring)     i += 1 

The while tests that the condition i < loopcount is true, and if true, if runs the statements that it contains. In this case, on each pass through the loop, i is increased by 1. Since loopcount is set to 7 on the first time through, the loop will run six times, for i = 1,2,3,4,5 and 6.

Once the condition is false, when i = 7, the while loop ceases to run.

(I don't know what your actual use case is, but you may not need to assign newcount, so I removed that).

Answer 2

From the range() docstring:

range([start,] stop[, step]) -> list of integers

Return a list containing an arithmetic progression of integers. range(i, j) returns [i, i+1, i+2, ..., j-1]; start (!) defaults to 0. When step is given, it specifies the increment (or decrement). For example, range(4) returns [0, 1, 2, 3]. The end point is omitted! These are exactly the valid indices for a list of 4 elements.

So, range(1, 10), for example, returns a list like: [1,2,3,4,5,6,7,8,9], so, your code is basically doing:

loopcount = 3 for i in [1, 2]:     somestring = '7'     newcount = int(somestring)     loopcount = newcount 

When your for loop is "initialized", the list is created by range().