I'm a beginner in python and using v2.7.2 here's what i tried to execute in the command prompt
p = 2
while(p>0):
for i in range(10):
print i+1 , p
p-=1
The expected output was
1 2
2 1
However the actual output is
1 2
2 1
3 0
4 -1
5 -2
6 -3
7 -4
8 -5
9 -6
10 -7
Why does this happen? and How do i achieve the expected behavior?
The while condition is only tested again after the for loop finishes. You could do this instead
p = 2
for i in range(10):
if p <= 0:
break
print i+1 , p
p-=1
This is the output I get:
1 2
2 1
3 0
4 -1
5 -2
6 -3
7 -4
8 -5
9 -6
10 -7
Your question as to why it runs. Your outer most conditional is a while loop, which is true upon the first execution, however it runs right into a nested for loop. When this happens the while, will not be checked until the for loop finishes its first execution (which is why p = -7).
What you want is this:
p = 2
for i in range(10):
if p <= 0:
break
print i+1 , p
p-=1
which gives output:
1 2
2 1
1 2 2 1 Thats what i'm looking for thanks!
i isn't changingWelcome to python :-)
You can try this:
p = 2
for i in range(1, p+1):
print i,
print
for i in range(p, 1, -1):
print i,
This will print the desired output. Not only for 2 but also if you change the value of p, it will print the same output.
range function can take three arguments viz start, stop and step. If you give range(x), it will take start as 0, and step as 1 and go up to x(x is not included). If you give range(y, x), it will start from y and go up to x with default step value as 1.
In the example, I used range(p, 0, -1) which takes start point as 'p', step as -1 and decrement the value of p until 1 and quits. To read more about range, click here.
