problems with looping, i suppose

[John Salerno]

Here's an exercise I was doing to guess a number from 1-100. Just for
fun (ha ha) I decided to add some error checking too, and now when I run
it, the DOS prompt flashes real quick and disappears. At first, I had
just the top try/except block and not the second one, and that worked
(as far as it would work), but after adding the second try/except, it
has this problem. I'm sure it has something to do with the looping and
the breaks/continues.

I'd appreciate any help on this, and also any suggestions for programs
that let you step through code to debug it (I'm used to Visual Studio).
I have SPE installed at home, but not here at work so I can't try it
right now. I assume it has a debugger.

Thanks.

 

[John Salerno]

Here's an exercise I was doing

This might help:

import random

number = random.choice(range(1, 100))
tries = 0

while True:
try:
guess = input('Enter a number between 1 and 100: ')
break
except NameError:
print 'Invalid number\n'
continue

while True:
tries += 1
try:
if guess == number:
print 'Congratulations! You got it in', tries, 'guess(es).'
break
elif guess < number:
guess = input('Too low. Try again: ')
elif guess > number:
guess = input('Too high. Try again: ')
except NameError:
print 'Invalid number\n'
continue

raw_input()

 

[John Salerno]

Here's an exercise I was doing to guess a number from 1-100.

Here's another question that is related:

while True:
year = raw_input('Enter year (or other character to quit): ')

try:
year = int(year)
except NameError:
break

if (year % 4 == 0) and (year % 100 != 0 or year % 400 == 0):
print year, 'is a leap year.\n'
else:
print year, 'is not a leap year.\n'

raw_input()

This works as expected, except that if you enter any character other
than a number, the program just quits. Why doesn't it still execute the
raw_input function and pause? I think this is what is happening in the
other exercise too, but I don't know why. If you break out of the loop,
should it still pause at raw_input?

 

[akameswaran]

Just barely looked the code answer:
check you scope on the second try block.

if that doesn't work...
I'll read it for real

Try PyDev plugin with eclipse - it's served me fairly well, but I did
come from Java - so I'm an eclipse fan already.

 

[John Salerno]

Just barely looked the code answer:
check you scope on the second try block.

if that doesn't work...
I'll read it for real

Try PyDev plugin with eclipse - it's served me fairly well, but I did
come from Java - so I'm an eclipse fan already.

I think it has to do with the exception I'm using. For the leap year
program, it should be ValueError. For the other one, its' a combination
of that and the input function.

 

[John Salerno]

I think it has to do with the exception I'm using. For the leap year
program, it should be ValueError. For the other one, its' a combination
of that and the input function.

Hmm, turns out something was wrong with the indentation of the second
while loop! Even though it looked correct, it created problems when I
opened it in IDLE, so I just unindented the whole thing and reindented
it manually, and now it works.

 

[akameswaran]

Ok I felt a little bad for my quick answer, these just seem like
homework problems.

first problem - it's scope. (there are two scope errors in the sample)
white space is meaningful. get consistent with tabs or spaces, or
choose an editor that replaces tab press with space. It'll make life a
lot easier. And make copy and paste from the group easier for people
trying to help

Second problem (leap year) , you are catching the wrong kind of
exception in that problem, so it's bubbling out as an unhandled
exception. Use IDLE as a starting point, it's not much - but it would
quickly expose these kinds of proboems.
Run your code using idle or the interactive and you will see what is
going on.

As a side issue. On the second problem - you did say you just want to
quit in the event of non numeric input, so it's WAD. But the
underlying exception generated is not a NameError. Try catching any
error and printing it.

 

[akameswaran]

Ha, you found it all before I could fire it up.
The whitespace thing is very odd, and it took about a month before I
was comfortable using it for scope.

On the bright side, scope errors are a lot easier to find than you
might think, once you get used to looking at py code.

I thought, if your in the mood to pay for software, and on windows -
wing IDE is used by many of my wrkmates. IT looks like garbage on
linux (at least to my eyes) so I stick with eclipse, but Wing has a lot
of fans.

 

[Gary]

John --
I looked at your exercise. As it appears in my browser, there appear
to be a couple of problems with the bottom "While" block.

0 Alignment problem with the "except" clause.
As I'm sure you've already discovered, Python is "whitespace
sensitive". If it looks like a block, it is; otherwise it isn't. The
"if" .. "elif" statements aren't "inside" ("to the right of") the
"try". Python will, I believe, interpret this as "try" with no
matching "except" or "finally" and will toss this as a syntax error --
and thus, I suspect, the flashing screen.

o logic error.
if "guess" == "number", program as written will print "congrats"
forever.

Assuming my "cut, copy, paste" works ok, try this: (hmm, the print
"congrats" line looks like it's broken into two lines when I preview
this. Please ignore -- it should all be on one line):

import random

number = random.choice(range(1, 100))
tries = 0

while True:
try:
guess = input('Enter a number between 1 and 100: ')
break
except NameError:
print 'Invalid number\n'
continue

while True:
tries += 1
try:
if guess < number:
guess = input('Too low. Try again: ')
elif guess > number:
guess = input('Too high. Try again: ')
else:
print 'Congratulations! You got it in
',tries,'guess(es).'
break

except NameError:
print 'Invalid number\n'
continue

raw_input()


I altered the "if" a bit -- just my own preference that an "if" always
have a matching "else".

If you're looking for something with an editor and a debugger -- try
"IDLE". If your installation is like mine, it's included. Look in
your Python directory under Lib/idelib for file "idle.pyw". (NB: At
the moment, I'm running a WinXP box and that's where it is here. My
poor old mind can't dredge up whether it's in the same relative place
in say, a Linux installation.) "IDLE" isn't perfect but it'll get you
started. (Also, FWIW, if you run this under "IDLE", you can omit the
trailing "raw_input()")

hope this helps.

gary

 

[John Salerno]

0 Alignment problem with the "except" clause.
As I'm sure you've already discovered, Python is "whitespace
sensitive".

Wow, I'm really confused. As it turns out, whitespace *was* the problem,
but it looks no different now (as it works) than it did then (when it
didn't work). I don't know if my copy/paste worked properly for you
guys, but as I see it in my newsreader, everything looks right.
try/excepts are indented inside whiles, if/else are indented within
tries, and if lines are indented under the ifs.

I just don't see where the problem was. Maybe it was a result of my text
editor doing whatever it does to auto-indent, because originally I
didn't have the while loop, so after adding it I had to indent the other
stuff. But it never *looked* wrong, so I don't get it...

Does what I originally pasted in my message look incorrect? To me, it
all seems indented properly.

 

[Scott David Daniels]

Here's another question that is related:

while True:
year = raw_input('Enter year (or other character to quit): ')
try:
year = int(year)
except NameError:
break
...
raw_input()

This works as expected, except that if you enter any character other
than a number, the program just quits. Why doesn't it still execute the
raw_input function and pause?

Here's a clue:
try:
try:
x = int('abc')
except FloatingPointError:
print 'never reached'
print 'This is not reached either'
except ValueError:
print 'proper exception'
raw_input('Pause and reflect:')

--Scott David Daniels
(e-mail address removed)

 

[John Salerno]

Ok I felt a little bad for my quick answer, these just seem like
homework problems.

NP. I appreciate your help. These are just little exercises I found
online, just to give me a reason to use Python.

 

[Sion Arrowsmith]

Does what I originally pasted in my message look incorrect? To me, it
all seems indented properly.

Yes. Somewhere or other you've got your tabstop set to 4, and python
treats literal tabs as being of equivalent indent to 8 spaces. As
does my newsreader, so the problem was obvious:

while True:
tries += 1
^ This was a tab (my cut&paste has turned it back into spaces)
try:
^ This was a tab too.
if guess == number:
^^^^^^^^ This was eight spaces even before I cut&pasted.

 

[John Salerno]

Yes. Somewhere or other you've got your tabstop set to 4, and python
treats literal tabs as being of equivalent indent to 8 spaces. As
does my newsreader, so the problem was obvious:

while True:
tries += 1
^ This was a tab (my cut&paste has turned it back into spaces)
try:
^ This was a tab too.
if guess == number:
^^^^^^^^ This was eight spaces even before I cut&pasted.

Ah, that makes sense now! Thanks!

 

[Lawrence D'Oliveiro]

... and now when I run
it, the DOS prompt flashes real quick and disappears.

Does your DOS OS not have the equivalent of xterm, or KDE Konsole, or
such? Something that lets you execute more than just one command, so you
can see the results of the previous command before the window disappears?